Management of air pollution

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8 MANAGEMENT OF AIR POLLUTION

8.1 Air Pollution Management Approaches

8.1.1 Outline of Existing Models 8.1.2 Analysis of Air Quality Problems

8.1.2.1 Decoupling of the Air Quality Problem

8.1.2.2 Analysis of Problems Related to Non Reactive Pollutants

8.1.2.2.1 Problems from Point Sources within Urban Areas

8.1.2.2,2Problems from Area Sources within Urban Areas 8.1.2.2.3Problems from Point Sources in Rural Areas

8.1.2.3 Analysis of Problems Related to Photochemical Pollutants

8.1.3 Analysis of Available Control! Options

8.1.3.1 Reduction of Emission Loads at the Source

8.1.3.1.1 Inspection and Maintenance Programmes

8.1.3.1.2Fuel Type and Quantity 8.1.3.1.3S0urce Modification

8.1.3.2 Reduction of Emission Loads Through Controls

8.1.3.2.1 Control Systems for Road Vehicles 8.1.3.2.2 Control Systems for Industrial Sources Reduction of the Emissions impact on Air Quality

8.1.3.3

8.1.3.4 Institutional Measures

8.1.3.4.1 Management of the Vehicle Kilometers Travelled 8.1.3.4.2 Relocation of Industrial Sources

8.1.3.4.3 Temporal Distribution of Area & Point Source

Emissions

8.1.3.4.4Management of the Population and Traffic Densities

esis of Rational Pollution Control Strategies

Short Term Air Pollution Problems

Annual or Seasonal Air Pollution Problems from Non Reactive

Pollutants

Photochemical Air Pollution Problems

Management of the Air Pollution Episodes

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8-2 Approaches for Consideration in Formulating Environmental Control Strategies

8.2 Air Quality Models

8.2.1 Short Term Critical Impact Analysis

8.2.1.1 Impact of Point Sources on the Critical Receptor 8.2.1.1.1 Introduction 8.2.1.1.2Description of the Model 8.2.1.1 3 Example 8.2.1.2 Impact of Point Sources on Any Given Receptor 8.2.1.2.1 Introduction 8.2.1.2.2Description of the Model 8.2.1.2.3Example

8.2.2 Long Term (Seasonal or Annual) Impact Analysis

8.2.2.1 Calculation of the Meteorological Parameters 8.2.2.1.1 Introduction 8.2.2.1.2 The Meteorological Parameters 8.2.2.1.3Example 8.2.2.2 A Model for Point Sources in Urban Setting 8.2.2.2.,1Introduetion 8.2.2.2.2 Description of the Model 8.2.2.2.3Example

8.2.2.3 A Model for the Dispersion of Traffic and Space Heating Emis- sions in Urban Setting

8.2.2.3.1 Introduction

8.2.2.3.2 Description of the Model

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Management of Air Pollution 8-3 8.1 Air Pollution Management Approaches

8.1.1 Outline of Existing Models

The analysis of existing air pollution problems and the formulation of control strategies through the systems approach described in Section 7.3 is facilitated in practice by the use of appropriate tools In this baok a number of such tools are offered:

The source inventory model given in Section 3.2.2 introduces the impact

of all major parameters into the assessment of the air emissions releases, and defines the data requirements from field surveys

This model is thus a valuable tool in air poltution inventory

studies, not only for computing the emission loads, but also for providing guidance on the data to be collected during the field survey work, and for organizing and presenting such data in a con- cise manner (see also Sections 3.2.3 and 3.2.4) The above constitute key elements in the analysis of the existing air pollution

problems

In addition, the model of Section 3.2.2 provides a fairly compre- hensive list of the alternative controls for each activity and each source therein, listing both the applicable process alterna- tives, as well as the established control technologies Further-

more, parameters that exert a particular influence on the emissions are identified and the impact of relevant changes can be quantified (e.g the impact from possible changes in the types and qualities of the fuel used can be easily quantified) The above

provide valuable guidance on the formulation of valid strategies for any given urban or industrial area, and make possible the

quantification of the ensuing air pollution load reductions

The Light Duty Gasoline Powered (LDGP) Vehicle emissions model given in

Section 3.3 supplements the main emission inventory and control model of Section 3.2.2, enabling the user to custom-fit the emission factors to the local and seasonal ambient conditions and driving patterns As both the exhaust and: the evaporative emissions from LDGP Vehicles are variable, the models presented in Section 3.3 deal with both of them The emphasis given on the LDGP vehicle emissions is justified by their particular importance to urban air pollution problems, especially during the ozone peak season, as well as by their significant local and seasonal variability

The flue gas volume model presented in Section 3.4, allows convenient assessment of the actual gas volume’ from external combustion sources as a function of the easily measured (or assumed) CQ concentrations The exit gas volume, along with other information (exit gas temperature, physical stack height, and internal stack diameter) and emission load data, are required for estimating the ambient concentrations from point sources through the application of dispersion models (see Section 8.2.1) As the majority of point

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sources, for which air quality models are applied are industrial or utility boilers, the model presented in Section 3.4 should cover a significant part of the gas volume data requirements

The stack temperature drop model presented in Section 3.5 allows conve-

nient computation of the stack-gas exit temperature, as a function

of the stack-gas inlet temperature and other variables (physical

stack height and diameter, and flue gas volume) It should be noted that although the flue gas exit temperature is a key vari-

able in air quality models, only the stack gas inlet temperature

is usually known from literature and/or from direct measurements The model given in Section 3.5 holds for both insulated and non-

insulated stacks and addresses the above input requirements of the

air quality models by properly interfacing the raw data which are

normally available from field surveys

Selected dispersion models, short term ones for point sources, and long term ones for point and area sources, are given in Sections 8.2.1 and 8.2.2 These models, despite their notable ease of use, offer prediction accuracies that rival these of sophisticated Gaussian dispersion computer models Moreover, the inputs to these models are streamlined and compatible with the outputs from the inventory models presented in Chapter 3 and introduced above

As mentioned in Section 7.3, the basic function of such dispersion models is to translate the emission loads, as predicted from the source inventory models under current or strategy conditions, into ambient air concentrations The latter constitute the criteria of effectiveness of any strategy, as they can be compared with the WHO air quality guidelines listed in Tables I.1-1 and I.1-2, or with the applicable national air quality standards The observa-

tion of such guidelines or standards constitutes, as we have seen, the typical objective of air pollution management studies

In relation to the compatibility of the predictions from the above

model with the guideline values listed in Appendix I, the following are noted:

(a) The point and the area source models used in this book are able to predict concentrations averaged over periods of one

hour, a season or a year, Their output can thus be directly

compatible only with the WHO guidelines or local standards, which are expressed as one hour average, seasonal mean, or annual mean concentrations

There are however, a number of WHO guidelines and local standards, which are based on different averaging periods, e.g 15 mins, 30 mins, 3 hours, 8 hours, or 24 hours (see Tables 1.1-1 and I.1-2) In such cases Equation 8.1.1-1 below can be

used to convert the above guidelines or standards into

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ty [p.185

We = Wi — | ( 8.1.1-1 )

In the above Equation, w, and t, are the limiting value, in

ug/m, and the averaging period, in min, of the applicable guideline or standard, while wy, is the computed equivalent "normalized" standard, in pg/mẺ, for an averaging period of

t,=60 min

Equation (8.1.1-1) is applied most appropriately for guide- Jines or standards expressed over averaging periods, t,, from a few minutes to a couple of hours Guidelines with averaging

periods of up to 24 hours could be "normalized", but with a

fair degree of uncertainty An example of the application of Equation (8.1.1-1} is given in Section 8.2.1.2.3

The computed "equivalent normalized" guideline value or standard w, is compatible with our model predictions and can be

used instead of w, in our analysis, as the inherent assump-

tion made is that if y, is observed, then w, will be also ob-

served,

(b) The carcinogenic risk estimates in Table I.1-3 could be used for providing limiting spatial-averaged (over the entire

urban area) or centre-maximum annual mean concentrations, which are compatible with the output of the area source

dispersion model described in Section 8.2.2.3.2 To do this,

a lifetime risk level, acceptable to the local society, should be defined

(c) The concentration of nitrogen dioxide (NO,) and Ozone (05),

can only be predicted through the used of appropriate photochemical models Simple photochemical models do not exist, and for this reason they have not been included in this book

If photochemical pollution is a problem in the study area, _the inventory models provided in Chapter 3 of this book can

be used for generating the necessary data, which can then be inserted into an appropriate photochemical computer model for further analysis

8.1.2 Analysis of Air Quality Problems

The objective of this Section is to describe the use of the air quality

models shown in Section 8.2 for air pollution management purposes

Through the use of these models, sources that cause violations of the applicable air quality guidelines or standards can be identified and the - severity of such violations can be assessed Moreover, the effectiveness

of pollution control measures’ can be assessed and the necessary

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8-G Approaches for Consideration in Formulating Environmental Control Strategies

conditions for meeting the applicable air quality guidelines or stan-

dards can be established

8.1.2.1 Decoupling of the Air Quality Problem

The air quality guidelines or standards can generally be divided into two classes One class aims at protecting human health from acute air pollution effects, and the relevant guideline values or standards refer

to short averaging periods, which span from a few minutes up to 24 hours The other class aims at protecting human health from long term

effects and the relevant guideline values or standards refer to annual and/or seasonal average concentrations Practical experience shows that the point and area sources exhibit distinctly different behaviour as far as the violation of each of the above classes is concerned Indeed: Observance of the short term guidelines or standards dictates to a large

extent the allowable emission rates and release conditions from point sources In other words, if point sources are made to operate without violating any short term air quality standards, their long term impact on any receptor will normally be near-negligible Observance of the long term guidelines or standards dictates to a large

extent the control measures in relation to area sources In other

words if area sources are made to operate without violating Tong

term (seasonal or annual) guidelines or standards, their short

term jmpact will be well within the relevant guidelines or stan- ards

The practical ramifications from the above observations are significant, for they allow the effective decoupling of the fairly complex overall

aiy quality problem into a number of simpler problems, each of which can be tackled separately In other words, separate analysis can be carried

out for each point source, or for each group of adjacent point sources, as well as for each type of area sources For the former task, point source models are given in Section 8.2.1, and for the latter task, an area source model is given in Section 8.2.2.3

Based on the above, the dispersion models given in Section 8.2 can be used effectively for the identification of existing violations of the applicable air quality guidelines or standards, as well as for assessing the effectiveness of any desirable control strategy More specifically:

The short term models provided in Section 8.2.1 can be used for predict-

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Management of Air Pollution 8-7

against all credible combinations of wind speed, stability class and mixing height, as well as against all receptor distances in cases where the latter is not fixed by the user

The Jong term model for the dispersion of area sources, which is given in Section 8.2.2.3, can be used for assessing the annual or seasonal spatial-average and centre-maximum concentrations over urban areas Separate assessments can be made for each type of source, and from these, the compounded impact from all sources can easily be computed The analysis can be carried out for both the current situation, as well as for any strategy scenario situation The decoupling of the complex overall air pollution problem into a num-

ber of simpler problems, each of which can be tackled separately from

the rest, leaves unaccounted the possible compounding of pollution lev-

els on any given receptor, from multiple point sources, as well as from

point and area sources While such compounding generally occurs, the

following conditions are believed to reduce the severity of this problem for the type of analysis carried out in our studies:

The critical receptor distance for most industrial point sources js of the order of a few hundred meters and only in few cases (e.g large power plants with stack heights of over 200 m) the critical receptor distance is of the order of 1 km Thus, unless major sources operate within a relatively close distance to each other, the compounding effect is weakened Moreover, the relatively low probability of winds coming from, or going towards, another nearby stack, has to be combined with the generally low probability of occurrence of the critical meteorological conditions for the stack under consideration (combination of the critical wind speed, critical stability class and critical mixing height) to produce situations, where the computed critical concentrations could be significantly exceeded due to impact from other upwind or downwind stacks The joint probability for the latter situation to occur tends thus to be small

The usual spatial distribution patterns for point and area sources in urban areas, indicate that area sources (mainly traffic and

space heating) have by far the highest densities in central areas,

where their concentration impact is also the highest Moreover, in urban areas industrial sources with significant emissions are rarely located near the city centre Thus, the locations where the area ane the point sources yield their peak concentrations do not coincide

It is always under unstable conditions that elevated sources produce critical conditions (stability classes A to C), Tables 8.2.1.1.2-1 and 8.2.1.1.2-2 On the contrary, by far the Tlargest

contribution from area sources is during stable conditions (D to F), Figures 8.2.2.3.2-1 and the example in Section 8.2.2.3.3 Thus

the meteorological conditions under which the area and point sources yield their maximum concentrations never coincide

The above differences in both the location and the meteorological conditions under which the maximum impacts of the point and area

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sources are exerted, make the interaction between them rather in- significant for the kind of criticality analysis performed in the

context of this book In other words, the impact of the point

sources on the annual or seasonal average concentrations at the

city centre (critical location for the long-term guidelines or standards) is small, and the same applies for the short term im-

pact of area sources on the computed critical hourly concentrations from point sources

Summarizing the above, the use of the short and long term models given

in Section 8.2 for the identification of the current air pollution prob-

lems and for the formulation of mitigation options offers significant practical advantages, but it has the following shortcomings, which the user should be aware of:

In the analysis of the existing situation most of the sources that are

likely to cause violations of the air quality guidelines or stan-

dards, especially the severe ones, can be expected to be revealed

The existence however, of some additional mild violations, or of violations which are somewhat more intense than these predicted,

cannot be excluded, due to the unaccounted compounding of pollu-

tion levels from multiple sources

In the formulation of mitigation options, all identified violations of the air quality guidelines or standards can be effectively ad- dressed on an individual basis However, some violations, probably

mitd, may still remain due to the unaccounted compounding of pol-

lution levels from multiple sources Based on the above, the derived mitigations options constitute necessary, but not necessarily sufficient conditions for the eradication of all possible violations

In reality the above limitations are not considered very restrictive,

except in unusual cases (e.g in cases where industries with major emissions operate near the city centre, or in industrial zones within urban

areas, where many plants with major emissions operate in close distance

from each other) Thus, the application of the models provided in Sec-

tion 8.2 should be considered sufficient for most study purposes It

should be kept in mind however, that after the analysis of the current

situation is completed and the desirable air poliution control strategy formulated, the use of an integrated computer model with site-specific meteorological data is strongly recommended so as to obtain a more com-

plete picture (e.g significance of the compounding effects, frequency

of violations) and to justify more fully the need for implementing cer-

tain costly measures

Naturally, the above discussion is valid for the dispersion of rela-

tively stable pollutants, as this is a prerequisite for the validity of

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8.1.2.2 Analysis of Problems Related to Non Reactive Pollutants

8.1.2.2.1 Problems from Point Sources within Urban Areas

The normal criterion, used in the assessment of stack impact, is the

maximum credible one-hour-average concentration on the critical re-

ceptor The critical impact analysis models provided in Section 8.2.1.1 simplify significantly the relevant analysis procedure For the application of these models the necessary input data requirements are listed

below:

The typical maximum hourly pollutant emission rates, The physical stack height,

The internal stack diameter at the exit level, Whether or not the stack is insulated,

The temperature of the gas at the stack exit level, The actual exit gas volume rate

The typical maximum hourly pollutant emission rates can be computed through the emission load model of Section 3.2, but typical maximum hourly activity data are required for this purpose The latter cannot be deducted directly from the annual activity data, which

are normally collected for our annual source inventory calcula-

tions (see Section 3.2.3 and 3.2.4), as the activity cannot be assumed to have a constant rate throughout the year Additional in-

formation about typical daily activity rates and hourly distribution profiles would normally have to be collected

Information about the physical stack height, the stack diameter and the stack insulation can be collected during each source survey visit

Data about the gas volume can in principle be obtained during each source survey visit However, reliable information may not always

be available, even for major sources, especially in cases where control equipment is not used In such cases one may use informa-

tion collected from other similar sources, and/or search litera-

ture for relevant information If the source under consideration

is an external combustion furnace, the model provided in Section

3.3 can be used for estimating the gas volume as a function of the fuel type and consumption In the latter case accurate estimates can be made if the CQ9 concentration in the flue gas can be mea-

sured Finally, the gas volume at its reference temperature wil} have to be converted into the corresponding volume at the stack

exit temperature through the ideal gas law (see example in Section

3.4.3)

The gas temperature is normally available, or can be easily measured, at

the source exit level It can thus be collected through the source survey visits From this temperature, and from the stack size and

the gas volume information, the gas temperature at the exit stack

level can be easily computed through the model provide in Section 3.4

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An example of the application of the above critical analysis procedure

for assessing the maximum credible one hour average ground concentration is given in Table 8.1.2.2.1-1 below Table 8.1.2.2.1-2 summarizes the results of this analysis for all industrial boilers in a study area firing residue fuel oi] Boilers burning low sulfur gaseous fuels and

distillate fuel oi] were excluded from the critical impact analysis as

they were not expected to cause violations of the applicable S0; guideline The computed maximum one-hour average SQ, concentrations can

be compared directly with the WHO guideline value of 350 ug/m?, and, as it can be seen, several violations could be expected to occur For these

cases the minimum stack heights required so as to have the WHO

guidelines observed have been computed and their values are also listed

in Table 8.1.2.2.1-2 A point to be made in relation to the data listed in Tables 8.1.2.2.1-1 and 8.1.2.2.1-2 is that computer printouts tend to list the computed numbers without much rounding, thereby increasing the accuracy Thus for example, the listed maximum one-hour SO concentration of 1185 ug/m? is accurate within + 20 % at best, and coul have been rounded to 1,200 pg/m

An alternative criterion, which may occasionally be used, is the impact

on a user-defined receptor This criterion could be used in cases for

example where sensitive receptors, such as hospitals or unique ancient

monuments, must be protected through the application of more stringent standards Depending on whether the applicable standards are short or

Jong term, the short term impact analysis models of Section 8.2.1.2 or

the long term point source model of Section 8.2.2.2 respectively can

also be used Naturally, there are other situations where the above models can be used For example, if one wishes to assess the long term

impact (seasonal or annual mean concentration) of selected point sources

in the city centre (so as to be considered along with the long term

impact of the area sources), the model 8.2.2.2 can be used

The data requirements of the short term impact analysis models in Sec- tion 8.2.1.2 are the same as these of the models in Section 8.2.1.1,

which were described above The exception is the distance from the

receptor, which this time is an additional model input (for the models in Section 8.2.1.1 the critical receptor distance was a model output) The Jong term point source model 8.2.2.2 has somewhat different input

data requirements from the models in Section 8.2.1.2 One or more sets

of the meteorological parameters mgq(k) (see Section 8.2.2.1) must be

provided, while annual activity data instead of the maximum hourly ac-

tivity data are used The latter relaxes somewhat the data requirements

as the annual activity data are collected for the annual source inven-

tory ralculations and are directly available (see Section 3.2.3 and

.2.4)

From the preceding discussion it appears that all sources, the impact of

which is to be evaluated, need to be surveyed This requirement is in line with the general procedural aspects discussed in Section 2.3

Indeed, all large-, as well as a number of medium-, size sources are normally surveyed and only these sources are normally subjected to crit-

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Table 8.1,2.2.1-1 Example critical impact analysis for an industrial

boiler (Plant # 18 in Table 8.1.2.2.1-2)

Data Collected: (Plant Survey Visit)

FUEL CONSUMPTION (MAX) : 2077.6 kg/hr SULFUR CONTENT IN FUEL : 3.5 weight % STACK PHYSICAL HEIGHT : 20.0 m

INTERNAL DIAMETER : 1.5m THERMAL INSULATION : NO

CO, IN FLUE GAS (DRY BASIS) : 11.0 Volume %

FLUE GAS TEMP AT BOILER EXIT : 240.0 %

AMBIENT TEMPERATURE : 20.0 %C

AREA TYPE (URBAN/RURAL) : URBAN

Set Objective: (Table I.1-1)

MEET WHO GUIDELINE F0R §0; : 350 ug/n 502

Calculation Procedure:

Max S02 Emission Rate (Section 3.2.2)

50, EMISSION FACTOR : 70,000 kg/MT Fuel 50, EMISSION RATE (MAX): 145.434 kg/h

Flue Gas Volume (Section 3.4.2)

FLUE GAS RATE : 16.376 Am3/s at 200°C

Temp Drop Through Stack (Section 3.5.2)

TEMP DROP THROUGH STACK: 2,7 ĐC EXIT STACK TEMPERATURE : 237.3 °C

Exit Gas Volume (Ideal Gas Law)

EXIT GAS VOLUME : 16.29 Am3/s

Max Allowable Normalized Critical Conc (Equ 8.2.1.1.2-5 & 6)

ALLOWABLE Coy 2406.6 po/m3/t/h

Critical Stack Impact (Section 8.2.1.1)

PLUME RISE MECHANISM : THERMAL CRITICAL STABILITY CLASS (A to F): C

WIND SPEED m/s: 9.2

RECEPTOR DISTANCE m: 82.1

CONCENTRATION, g/m?/t/h: 8145.5

MAX POLLUTANT CONCENTRATION, ug/m3: 1184.6

Alternative Mitigation Options (Section 8.2.1.1)

MINIMUM STACK HEIGHT, im: 40

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Table ð,1,2,2,1-2 Example summary of critical stack impact analysis results 8-12 Approaches for Consideration in Formulating Environmental Contre! Strategies (Page 1 of 2) f= BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOTLER BOILER BOILER BOILER BOTLER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOILER BOTLER BOTLER BOILER BOILER BOILER BOTLER of of of of of of of of of of of of of of of of of of of of of of of of of of of of of of of of of BOILERS of Analysis of Boiler # Analysis of Boiler # of of of of of of PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT PLANT ee ee es Be Sk Sổ Sạ # # Sh OAR SR SRR 4 5 8 9 10 11 12 13 15 16 17 18 18 20 22 23 ¿4 25 26 27 28 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 46 47 48 49 |

Max 1hr-Ave Min Stack

Stack Height 502 Stack Exit Stack Exit $0 Concent Height

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Table 8.1.2,2,1-2 Continued (Page 2 of 2)

"

Max Ihr-Ave Min Stack

Stack Height $02 Stack Exit Stack Exit $09 Concent Height

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8.1.2.2.2 Problems from Area Sources within Urban Areas

The normal criteria, fer assessing the impact of the area sources is the long term (annual or seasonal) city-centre maximum concentration, but, occasionally, the long term spatial-average concentration may also be used, The former is directly compatible with long term guidelines on standards, such as those listed in Tables I.1-1 and 1.1-2 Tables I.1-3

and 1.1-4 could also yield compatible limiting values if the maximum

lifetime risk for an individual, which is acceptable by the society, is

defined The latter better characterizes the exposure of the entire

urban population and can be compatible with relevant guidelines or standards Tables I.1-3 and I.1-4 could for example yield compatible

limiting values, if the average lifetime risk, which is acceptable by the society, for the urban population is defined

The area source model given in Section 8.2.2.3, allows convenient compu-

tation of both the long term city-centre maximum and spatial-average

concentrations for each type of area source separately, as well as the compounded total from all area sources The required data inputs include the set of meteorological parameters »(k) (see Section 8.2.2.1), the

effective diameter of the city, the annual or seasonal mean emission density, and the ratio of the city centre over the spatial average emission densities

The effective radius of the city (radius of an ideal circular city with

area equal to that of our study area) can be computed from the

following Equation:

R = (A/n)-5, (8.1.2.2.2-1)

where R is the effective radius in km and A is the actual area of

the city in km2

The mean emission density Qmean for each type of source (e.g space heating furnaces or Light Duty Diesel Powered cars) and for each

pollutant can be computed by dividing the total annual or seasonal

emission loads (as computed through the source inventory procedure, see Section 2.3) by the known area of the city Qmean 78

normally expressed in t/km2-y

The ratio of the centre maximum over the spatial average emission densi-

ties, P=Qnax/Gmean> characterizes the emission density profile

over the city The raw data, which are normally available for the

emission inventory (e.g the total distillate fuel of] consumption for space heating furnaces, or the annual average milage for a

particular type of vehicle) normally refer to the entire study

area allowing one to compute Qnean Rarely however, can separate sets of such data be found for the city centre Therefore, for the assessment of Qmax additional information is required

Two approaches are generally available for the assessment of P

One is based on the calculation of Qmax by collecting the raw

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area, annual fuel consumption data for the space heating furnaces

can be collected on a building-by-building basis) The second ap-

proach is based on a direct assessment of P through the use of appropriate indicators For example, it may be assumed in certain

situations that the density of emissions from space heating is proportional to the density of the population or to the building volume The factor P can then be estimated directly as the ratio

of the known city centre to spatial average population or building

volume densities

The area source model given in Section 8.2.2.3 is usually applied for the calculation of the annual average concentrations and for this pur-

pose the annual emission rates and meteorological data are used as inputs In certain cases however, seasonal concentrations may have to be estimated instead For the latter purpose the meteorological data, upon

which computation of the parameters @(k) are based, as well as the emission density, Qmean» and the ratio P=Qnay/Qmean, must be representative of the season under consideration it is interesting to

note in this regard that the "season" need not be a continuous time period, such as the winter months It can also be the morning shift of all working days, or hour 06 of each day of the year This way, the model of Section 8.2.2.3 becomes an extremely potent tool for analysing the impact of temporal distribution of emissions on air quality

8.1.2.2.3 Problems from Point Sources in Rural Areas

The normal criterion, for assessing stack impact, is the critical, one

hour average concentration on sensitive user-defined receptors Typical

receptors of this sort are the closest residential areas, hospitals etc, over which guidelines or standards for the protection of human health, such as those in Table I.1-1, must be observed The critical, one hour average concentration on the critical receptor might also be used in certain cases as a screening criterion in relation to the health of workers or to the protection of terrestrial vegetation (see Table I.1- 5)

The appropriate point source models for the analysis are those given in

Sections 8.2.1.1 and 8.2.1.2 The entire data collection and analysis procedure is identical to that described in Section 8.1.2.2.1, except that, the urban rather than the rural part of the models must be used 8.1.2.3 Analysis of Problems Related to Photochemical Pollutants

The level of the photochemical pollutants (mainly NQ» and 03) is generally more difficult to predict through the use of photochemical models than that of non reactive pollutants through the use of Gaussian dispersion models

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8-16 Approaches tor Consideration in Formulating Environmental Control Strategies

Because of the uncertainties involved, a typical procedure is to measure the hourly NOg and 03 levels through the monitoring network and apply an

appropriate photochemical model during selected episodic events so as to have its predictions verified The verified model can then be used to

predict the required reduction in the VOC emissions, which would be necessary to prevent violation of the relevant guidelines or standards As each VOC reduction prediction applies to a specific episodic event, a number of such events must normally be simulated so as to obtain a more valid overall picture

Simple photochemical models do not exist, and for this reason they have not been included in this book The emissions load models however, provided in Section 3.2 and 3.3, are valuable for the preparation of the necessary inventory inputs to the photochemical models, in cases where the use of the latter appears necessary

8.1.3 Analysis of Available Control Options

8.1.3.1 Reduction of Emission Loads at the Source

The present category comprises measures, which rely on the reduction of

the generated Toads at the source, rather than on their contro] after-

wards Some of the measures in this category have significant impact, are highly cost effective, and easy to implement Thus, some of the highest priority measures in rational air pollution control strategies are likely to belong in this category Reduction at the source represents a promising approach for air pollution control

8.1.3.1.1 Inspection and Maintenance Programmes

Proper inspection and maintenance (I/M) programmes are beneficial for

reducing the emissions generated from most types of sources In this

section the discussion will be limited to the I/M programmes for external and internal combustion sources, as they are particularly

effective and exert a significant impact on the quality of air,

especially over urban areas

Industrial boilers firing fuel oi] are common in both urban and rural

areas They emit significant loads of TSP (black smoke), 509, and NO, A number of parameters, which include excess air used, burner and boiler design, preheating of the fuel, as well as age and state of maintenance of the burner and boiler, affect both the

Trang 17

proportionally to fuel consumption Smoke however, exhibits a far

greater sensitivity and can be reduced by up to 80%

As an example, in the Greater Athens Area, a feasibility study carried out in 1983-1984 showed that the average smoke emission

factor for the residue oil fired boilers was 2.25 kg/tn of fuel consumed and that this could be lowered to 1.1 kg/tn of fuel consumed through proper I/M procedures (Economopoulos, 1987) A more

recent study demonstrated that the above objective was surpassed, as the average 1991 smoke emission factor was 0.86 kg/tn of fuel,

and that a further decrease was possible down to 0.73 kg/tn of

fuel (Economopoulos, 1991) In addition, the measured increase in

the internal boiler efficiencies, resulted in about 7 % lower fuel

consumption and this was translated into a further 7 % decrease in

black smoke emissions and another 7 % decrease in S502 and NOy emissions As black smoke and SQ constituted in 1985 the prime air pollution problem of Athens, the environmental benefits were

considered significant Along with them, the fuel consumption savings resulted in net economic gains to both the industries

involved and the national economy in general

I/M programmes for industrial boilers are easy to implement, and can be quite successful if properly planned for a smooth start A feasibility study can indicate the potential environmental and

economic benefits for the boilers in the study area, can define an inspection programme and the manpower requirements for its implementation, can set acceptable operating ranges and reporting procedures, and can recommend fines for violations A properly

planned programme can be successfully implemented with only a

smal] number (e.q 2 to 5) of properly trained inspectors

Central space heating furnaces are often fired with distillate fuel oi] and can be important contributors to the air pollution problem (mainly black smoke, SOe, and NOx) Indeed, emissions densities

are high in densely populated areas, the effective release height

is lower than that from industrial boilers, and the temporal dis-

tribution is highly irregular with most of the annual emissions

released within the coldest winter months and in some cases the daily emissions released within a few hours of the day

As in the case of the industrial boilers, the emissions and the

fuel consumption are highly dependent on the type and age of the equipment used and on the quality and frequency of the maintenance provided For example, in the Greater Athens Area, a feasibility

study carried out in 1983-1984 showed that the average smoke emis-

sion factor for distillate oil fired boilers was 1.64 kg/tn of fuel and that this could be lowered to 0.46 kg/tn of fuel though proper I/M procedures (Economopoulos, 1987) In addition, the

measured increase in the internal boiler efficiencies, indicated that about 10 % lower fuel consumption was feasible and this would be translated into a further 10 % lowering of the black smoke

emissions and another 10 % lowering of the SOo and NO, emissions

In a study currently underway (Economopoulos, 1992), the situation

appears to have improved since 1985, due to mandatory annual

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8-18 Approaches for Consideration in Formutating Environmental Control Strategies

boiler maintenance requirements However, as the number of boilers in the study area is large, about 250,000, and the inspection in-

adequate, the 1985 target has not been achieved The latter is at- tributed to infrequent maintenance of the boilers and to the low quality of the maintenance work In relation to the latter, most of the boilers maintained over the current winter season could be readjusted to achieve several percentage points higher internal thermal efficiency and a drastic reduction in smoke emissions Overall statistics are not yet available, but the differences were so significant that the impact of improper maintenance emerged as a factor of prime importance

Based on the above, the 1/M programmes for central heating boilers are important both for environmental and economic reasons, but their implementation is hampered by the large number of boilers in the study area Inadequate inspection was found to result from both infrequent boiler maintenance and from improper quality of maintenance To address the above problems, the following I/M implementation strategy was developed, and is in the process of being implemented within the Municipality of Athens (Fconomopoulos, 1991 & 1992):

Inspection over a large metropolitan area or region is carried out through a Central Computerized Enforcement Unit, which relies on axternal licensed mechanics to regularly inspect and maintain the boilers and to issue the boiler maintenance reports, on a few internal inspectors to check the quality of work of the licenced

mechanics, and on a computer system to keep tight control of the

boiler maintenance progress and of each licensed mechanic’s performance record

More specifically, building superintendents are asked to send by mail the reports produced by the licensed mechanics upon comple- tion of the boiler maintenance, and the received data are entered in the computer for analysis Warning letters are automatically

printed to building superintendents failing to abide, and fines

are issued if no corrective action is taken An inspection

programme is automatically generated aimed at checking the quality of work of, and the accuracy of the information supplied by, each

licensed mechanic

The central points in the philosophy of the above scheme are the following:

1 The building superintendents are responsible only for the

timely maintenance of their boilers and not for the quality of maintenance work performed For the latter the responsibility rests with the licenced mechanic, who issues the maintenance report

2 The central computerized enforcement unit, needs not enforce

the law through periodic inspection of hundreds of thousands of buildings, but rather to ensure that the quality of work of a Few hundred licenced mechanics is up to acceptable stan-

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8-19 Management of Air Pollution

Road vehicles are responsible for most of the NO,, CO and VOC, as well

as for a fair fraction of the black smoke and S02 emissions in ur-

ban areas As in the case of industrial and space heating boilers, emission loads and fuel consumption are highly dependent on the type and age of the vehicle and on the quality and frequency of the maintenance provided

The effectiveness of I/M programmes depends to a Targe extent on the age of the vehicles and the pollution control technology used As a general rule the older and the more polluting the vehicle, the more effective the I/M programme For example, a feasibility

study carried out in 1983 showed that for the aging fleet of Light Duty Gasoline Powered (LDGP) cars of Athens at that period a strict I/M programme could be expected to reduce CO emissions by 25-40 %, VOC emissions by 15-25 % and gasoline consumption by

about 7 % (Economopoulos, 1987) Somewhat lower effectiveness of 1/M programmes can be expected for modern conventional LDGP cars according to a recent study by TNO (1990) Indeed, for the

category of modern conventional (non catalytic) cars the anticipated reduction of CO is about 25 %, of VOC about 15% and of fuel consumption about 3 % It is interesting to note that the

emissions from LDGP cars equipped with 3-way open loop catalyst show the highest sensitivity to proper tuning with the CO and VOC

emissions reduced by 40 % and 35 % respectively while the NO,

increased by about 12 % On the other hand emissions from LDGP

cars equipped with 3-way controlled catalysts were found to be

practically unaffected by maintenance

The implementation of effective 1/M programmes for Diesel Powered vehicles is relatively simple, since visual observation can be used for screening the passing vehicles and for identifying those likely to be untuned (high black smoke emissions are clearly visi- ble), and a short test on the road can be used for testing the

compliance of the latter to relevant regulations Through the

above system, and with only a few mobile inspection teams, it was

possible to achieve effective implementation of I/M programme for

Diesel Powered vehicles in the Greater Athens Area This, along with the I/M programmes for industrial and space heating boilers, contributed to the lowering of the annual mean levels of black

smoke in the city-centre from 185 pg/m? in 1985 to its present level of about 100 ug/m

Effective I/M programmes for LDGP vehicles are more difficult to implement as the number of vehicles is usually far larger, visual screening on the road is not feasible, short tests have serious limitations, and finally the general public is affected It should be noted in this regard that short tests are more suitable for conventional cars with carburettors and, in any case, can only be

used to distinguish gross violations Proper tests on the dy-

namometer on the other hand are far too expensive for they involve costly equipment and require time to be completed To get around this problem, the maintenance procedure is based on the periodic checking of all engine components that affect the emissions and

their adjustment according to the car manufacturer recommenda-

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nents function as specified by the manufacturer, the emissions

will be at the manufacturer certified level The above procedure solves, aven though indirectly, the maintenance part of the problem, but leaves unanswered the inspection part of it In view of

the above limitations the following implementation strategy has

been formulated and proposed for the city of Athens (Economopoulos et al, 1992):

1 The owners are responsible only for the periodic maintenance of their vehicles and for not tampering with the emission control systems (removal of catalyst and lambda sensors, if any) Compliance of the owners can easily be established through

sporadic on-the-road checks, of valid maintenance certificates

and through visual inspection of the physical existence of control systems

2 Maintenance certificates are issued by authorized garages,

which are solely responsible for the quality of their work The latter is verified through a small number of inspection teams, which, on a random basis and without prior notifica- tion, check the tuning of certified cars on the spot, upon their exit from the garage

This way, the inspectors need not measure the emissions from a very large number (e.g several hundred of thousands) of vehicles,

but rather can ensure that the quality of work of a very small number (e.g a few hundred) of authorized garages is satisfactory

Centralized government-operated testing stations provide an alternative approach for emission testing and the issuing of valid maintenance certificates This may be particularly advantageous in situations where periodic testing of the vehicle road safety systems already takes place This approach however is not without disadvantages, as the capacity of the existing facilities, where they exist, may not be sufficient for the periodic inspection of all vehicles, and as the maintenance and adjustment required, especially for older cars, is normally carried out elsewhere, for example in private garages from where the maintenance certificate could be directly issued

Undoubtedly, effective I/M programmes exist for many types of sources

and proper implementation strategies that suit local conditions in each

particular study area need to be formulated The discussion above was necessarily restricted to only a few types of sources The purpose of describing the above implementation strategies is to illustrate a suitable procedure rather than to define or recommend particular approaches

8.1.3.1.2 Fuel Type and Quantity

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from various fuels used in external and internal combustion sources are illustrated in Table 8.1.3.1.2-1 It can be seen that fuel combustion is a contributor to the traditional black smoke - 502 urban air quality

problems, as well as the more recent photochemical smog pollution

Table 8.1.3.1.2-1 Major Emissions from Various Fuel Uses (see also

Section 3.2.2)

Utility Boilers

Industrial Boilers Space Heating Boilers Diesel Powered Vehicles Gasoline Powered Vehicles LPG Powered Vehicles

The strong dependence of the emission factors on the fuel type and qual -

ity on one hand and the usual possibility of changing fuels with only minor equipment modifications on the other, provide the opportunity to planners not only for Tong term, but also for very effective short term measures In addition, measures of this sort are the easiest to impte-

ment as the pollution control authority does not have to deal with each

of the humerous sources in the study area, but rather with the usually few fuel production and/or central distribution channels It is there-

fore by no chance that measures related to the use, the type and the

quality of fuels are often among the most effective control measures in air pollution control strategies Indeed, most of the earliest air pol-

lution contro] success cases were based to a large extent on such measures,

Reduction of the quantities of fuel used is a rather obvious, and cer- tainly sensible, way to limit emissions This can be achieved through proper Inspection and Maintenance programmes (see Section 8.1.3.1.2), through fuel savings in industrial processes (e.g over 60 % fuel savings were found to be possible with relatively simple

measures from the Textile industry operating in the Greater Athens

Area), through better thermal insulation of buildings, through road traffic management, through expansion and better organization of the public transport system, etc As these measures yield not only environmental, but also significant economic benefits, they should be carefully considered in the context of any air pollution

management study

The type of fuel used in external combustion sources is a key parameter that affects the emitted loads Table 8.1.3.1.2-2 below lists typical emission factors for some alternative fuels, often used in

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illustrates the significant impact when shifting from residue fuel oil to distillate fuel oi] and to gaseous fuels Such impacts may

be far more dramatic when shifting from the use of solid fuels or from the use of fuels which are unsuitable for the particular

combustion source (e.g use of residue fuel oi] in space heating

furnaces) More detailed information about the impact of the fuel type on emissions can be obtained through the model in Section 3.2.2

Table 8.1.3.1.2-2 Comparison of Emissions from Selected External Com- bustion Sources (see also Section 3.2.2)

NOy

kg/tn

Electric Power Stations

Residue Fuel 0i1! Natural Gas _— 32 14.00 8 wo Industrial Boilers Residue Fuel Oi1! 1.32 14,00 7.0 Distillate Fuel 0112 0.28 6.00 2.8 Natural Gas 0 0.01 2

Space Heating Boilers

Distillate Fual oi1¢ Natural Gas mm on „36 6.00 01 coo

Assumed Sulfur content in residue fuel oi] of 0.7 weight %

Assumed Sulfur content in distillate fuel oi] of 0.3 weight %

The usually significant cost differences among alternative fuels

and the frequent limitations on the availability and/or on the production of certain fuels, often place severe constraints on the

practical possibilities of fuel type changes However, planners may be able to achieve significant environmental gains through these changes, especially when considering the cost and

implementation difficulties associated with alternative options Indeed, installation of control equipment, such as dust control

and especially desulfurization units, is economically and practically feasible only for large-size units On the other hand

changes to environmentally superior types of fuel are generally feasible for most types of boilers and furnaces, can be imple-

mented with relatively limited equipment modifications (e.g adjustment or change of burners) and do not require new fuel

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The type of fuel used by road vehicles is a key parameter that affects the emitted loads Table 8.1.3.1.2-3 below lists typical emission factors for common alternative fuels for the important Light Duty vehicle category for the purpose of illustrating the magnitude of differences involved More detatled information about the impact of the fuel type on emissions from road vehicles can be obtained from the models in Sections 3.2.2 and 3.3

8.1.3.1.2-3 Emissions from conventional Light Duty vehicles

made between 1981-84 under typical urban driving conditions (see also Section 3.2.2 and 3.3) smoke $02 x co voc gr/km gr/km gr/km Diesel oiTl Gasoline2 LPG l

1 Assumed Sulfur content in Diesel of] of 0.3 weight %

Evaporative VOC emissions from the vehicle itself, as well as from

the gasoline distribution system, are not included,

The only practical short-term control options for a given fleet through fuel type changes is the conversion of gasoline powered vehicles into LPG (or possibly into natural gas) powered ones, This may be particularly effective in reducing the CO and the Voc emissions This may be a sensible way to abate the photochemical pollution over a relatively short time period without having to

resort to forceful restrictive measures Prerequisites however for

the application of this measure are the availability of LPG and of LPG distribution infrastructure {LPG dispensing stations) Moreover, feasibility and implementation studies will be required,

which will define the particular vehicles to be converted (vehicle

age-range, vehicle use, etc), and justify through a cost/benefit analysis the proposed measure These studies will also analyse the

safety of the existing and new infrastructure (analysis of safety and regulations in relation to the location, construction and

operation of LPG dispensing stations, the LPG truck routing, the conversion of the gasoline-powered vehicles into LPG-powered ones, etc)

On a medium-term basis the possibilities of LPG (or possibly natural gas) use can be increased by encouraging current users of

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This may be particularly effective in urban areas with high black smoke and S$Q9 jevels and a sizeable fleet of light duty diesel

cars (Economopoulos, 1987) From the implementation point of view

the measure can be particularly successful if targeted at categories of light duty cars, such as taxis, travelling long distances per year For these vehicles the associated renewal rates are faster and the choice of the new vehicle to replace the old one is more sensitive to fuel pricing considerations The prerequisites for the implementation of the present measure remain similar to those for the short term measures examined above

The quality of fuel used by external and internal combustion sources is an additional important parameter that significantly affects emissions In many cases improvements in the quality of fuel are less costly and far easier to implement than changes in the fuel type As a general rule, improved quality of fuel does not involve any equipment changes other than proper adjustment and may even prolong the equipment life

In relation to the external combustion sources (Section 3.2.2) it can be seen that:

1 The TSP emissions from coal fired boilers are directly related to the ash content of the fuel;

2 The TSP (black smoke) emissions from residue fuel oi] powered boilers are related to the sulfur content of the fuel, 5, through the empirical relation

e smoke = 0,39 + 1.3*§, kg/tn of fuel used

3 The SO, emissions from the use of any fuel are directly related to the sulfur content of the fuel used;

4 The NO, emissions from residue fuel ot] powered boilers are

related to the Nitrogen content of the fuel, N, through the empirical relation

Oyo, = 2-8 + 50*NZ, kg/tn of fuel used

In relation to the internal combustion sources, (Section 3.2.2 and

3.3) it can be seen that:

1 The evaporative VOC emissions from gasoline powered vehicles,

which may account for up to 30 % to the total VOC emissions from traffic, depend significantly on the volatility of the gasoline

2 The SO, emissions from diesel powered and gasoline powered cars are directly related to the sulfur content of the fuels

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The photochemical reactivity of the emitted hydrocarbons, and

thus the intensity of the photochemical pollution, is very

much dependent on the quality of the gasoline used Relations which quantify this impact have not been established, but

gasolines with higher fractions of unsaturated double bonds,

such as olefins (e.g ethene, propene, butadiene), or aromat- ics (e.g toluene, xylene, trimethylbenzene) exhibit the greatest photochemical reactivity

Lead emissions from gasoline powered cars are directly related to the lead content of gasolines used However, Towering of the Tead content often necessitates reformulation to enhance the octane number, which increases the aromatic content of the gasolines and hence the photochemical reactivity of the emitted hydrocarbons It may also increase the volatility of the gasolines, due to the addition of volatile butane compo - nents which enhance the octane number, and this increases evaporative VOC emissions Both of the above changes in gasoline composition tend to intensify the photochemical pollution problem

The quality of diesel as expressed through the cetane number (related to the ignitton quality}, the distillation range, and the aromatic content, considerably affects the emissions of

all major pollutants In the emissions model of Section 3.2.2

the impact of poor fuel quality is grouped with the age of the fleet and the state of maintenance, as reliable relations between fuel quality and emissions have not been established It is believed however, that cetane numbers below 50 tend to in-

crease all pollutants, while tails in the distillation curve above 400°C tend to increase the smoke emission rates A rough quantitative idea about the impact of cetane number on the

emission rates is given in the table below, but it should be stressed, that data from the different sources vary widely:

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Change in Cetane Number from 52 to 47.5 8-26 Approaches for Consideration in Formulating Environmental Control Strategies Change in Cetane Number from 52 to 44.5 c0 + 19.0 % + 31.5 % voc + 38.0 % + 63.0 % NO, + 5.5 % + 9.0 % Smake — + 23.0% + 38,0 %

Based on the above, planners have a fairly large array of alterna-

tive control options to abate particular air pollution problems through fuel quality improvements Indeed:

If the problem in our study area is of the high black smoke and SOo type, a particularly effective way to control it is through the lowering of the sulfur content of the fuels used in internal and external combustion sources This also contributes to the reduction of the black smoke emissions from residue oi] fired industrial boilers and diesel powered vehicles, as well as to the lowering of VOC emissions from gaso- Jine powered vehicles An additional significant measure might be the improvement of the quality of Diesel oil, which could be particularly effective in lowering the smoke emissions from traffic

If the problem in our study area is photochemical smog, one

could consider the possibility of lowering the gasoline

volatility, which can reduce in turn the evaporative VOC emissions An additional measure could be the improvement of the gasoline quality so as to have less photochemically reac-

tive hydrocarbon emissions Moreover, lowering the nitrogen content in the residue fuel oil used (refineries can achieve

this by processing crude oils of appropriate quality) may be a

fast and effective way to reduce the NOy emissions from utility and industrial boilers

If the lead level in our urban study area is high, an effective way to reduce it is through the lowering the lead content of the gasolines used This however, may have to be balanced against a possible increase in photochemical pollution due to

the possible increase in the chemical reactivity of the

emitted hydrocarbons and/or due to the possible increase in the volatility of the resultant gasolines

As discussed above, measures involving changes in the type and/or the quality of fuels used by the internal or external combustion sources in

the study area are often significant from the environmental point of

view, as well as cost effective on a relative basis Through the tools provided in this book, the environmental impact of alternative scenarios can in principle be established and thus their relative importance pri-

oritized However, the sheer magnitude of such measures, the possible costs involved on an absolute basis, the supply and/or production con-

straints which always exist, and the implementation aspects need to be

carefully considered in advance, Close cooperation with relevant author-

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fuel producers and/or suppliers (e.g from the local refineries) is normally necessary for defining priorities from the cost/benefit point of

view and for deciding where it is practical to draw the Tine

8.1.3.1.3 Source Modification

In many situations source modification is the only practical way to reduce emissions In several other situations source modification reduces emissions more effectively than does the addition of control systems Thus, measures of this type are likely to be among the highest priority measures in any control strategy

(a) Modification of Road Vehicle Fleets

There are few proven possibilities for the use of retrofit control systems on existing road vehicles for the purpose of reducing their emissions in a study area Type approval requirements for each retrofit de-

vice on each particular vehicle model, and severe additional technical

constraints make this approach impractical for large scale applications

The only practical technical possibilities for reducing road traffic emissions are thus the vehicle I/M programmes, discussed in Section

8.1.3.1.]1, the fuel type and quality improvements, discussed in Section 8.1.3.1.2, and the modification of the fleet structure

A vehicle fleet is characterized by its magnitude, by the age and size distribution of the vehicles in it, and by the control technologies

employed In most developing countries conventional technologies are predominant, while vehicles tend to remain in service for a very long

time The latter is particularly negative from the environmental stand- point, since, on one hand it delays for many years the introduction of modern cars, which are designed to have much lower emissions even with

conventional technologies, while on the other hand an old-technology and highly polluting car becomes even more polluting with age as its

components deteriorate

A rather obvious control measure for many urban air quality problems is

the renewal of the aging vehicle fleet This may appear an expensive

proposition, but, as a technoeconomic study in Athens demonstrated, from

the national economy point of view, the optimum average life span of

private LDGP cars is about 12 years Indeed, increasing repair costs, a widening fuel consumption between old and modern cars, and the increasing frequency of accidents, makes the use of old vehicles uneconomical past a certain age The optimum retirement age depends on the type of

vehicle and on its use, and may vary from country to country However,

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their replacement with modern cleaner ones The impact of relevant mea-

sures can be assessed through the inventory models of Section 3.2.2 and

3.3, while a technoeconomic study can indicate the precise target and

nature of the incentives to be offered so as to avoid excessive bur- dening of the national economy (b) Modification of Industrial Sources

Technical measures for the control of industrial emission often involve

process modifications rather than the installation of control systems

For example:

Changing the splash filling of underground gasoline tanks in ser-

vice stations into submerged filling, introducing vapour balanced filling of cars and underground tanks, or converting fixed roof gasoline storage tanks to floating ones in bulk gasoline termi-

nals, are some of the relatively simple and cost-effective process

modifications available for reducing the VOC emissions in the study area

Conversion of open storage areas for non metallic minerals into

enclosed ones, or the application of petroleum resin products on unpaved industrial roads, or the cleaning of city streets, repre-

sent some of the measures available for reducing the TSP emissions

Several of the source modification measures, like the ones mentioned above, are listed in the inventory model of Section 3.2.2 and their impact on the emissions can be directly assessed Other source modification measures also exist, which are not explicitly listed in-, but their impact can be quantified through-, the inventory model of Section 3.2.2

For example, the use of high solids paint-systems, which require less

solvent thinning, or the replacement of solvent-based paints with water- based ones (Latex dispersion paints, water-born top-coats and water-

paints) for industrial or architectural surface coating applications,

are measures which reduce the quantities of solvents and/or paints used and, once the magnitude of such reductions is known, the relevant impact in the reduction of the VOC emissions can be easily computed Finally, a

number of important process modifications, not yet widely employed, are not listed in-, nor can their impact be assessed through-, the inventory

model of Section 3.2.2 These measures include the Combustion Modifica- tions (In-Furnace Reduction, Two Stage Combustion, Low NO, Burners, Am- monia NO, reduction, etc), which can significantly reduce the NOy emissions from utility and large industrial boilers, as well as from various

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8.1.3.2 Reduction of Emission Loads Through Controls

The reduction of the generated loads at the source through the tech-

niques discussed in Section 8.1.3.1 represents a rational and often cost

effective approach Emissions however remain, and the use of contro]

technologies to reduce the loads, which are eventually released in the atmosphere, represents the next, and perhaps the most widely known, Tine of defence

8.1.3.2.1 Control Systems for Road Vehicles

The spectacular improvements, especially in the Otto engine design, over

the past decade have resulted in the progressive and rather precipitous

reduction in emissions This is reflected in the values of the emission factors for the various age groups of Light Duty Gasoline Powered (LDGP) cars in the models of Sections 3.2.2 and 3.3

As a result of this progress, conventional (non catalytic) LDGP cars with fairly low emissions are currently available, as well as catalytic ones with increased longevity of control systems Moreover, improvements

are also evident for diesel-powered vehicles, especially for the heavy-

duty ones Indeed, based on the CEC technical justification for the

latest emission standards listed in Table 8.1.3.2.1-1, further

significant progress can be expected over the next few years in relation to the reduction of both black smoke and 502 emissions through improved engine design, possible use of smoke oxidizers or smoke traps, as well

as through the use of diesel oils with very low sulfur content

High black smoke and S09 levels constitute the oldest form of urban air

pollution Such problems remain even today, yet the origin is shifting from the space heating and industrial sources to traffic Indeed:

Heavy duty vehicles are normally diesel-powered and their impact

may be significant in large urban areas, particularly in relation to black smoke and SQ9 problems Inspection and maintenance {see Section 8.1.3.1.1), improvements in the quality of diesel oil (see

Section 8.1.3.1.2), and renewal of the aging fleet with modern low

emissions vehicles (see Section 8.1.3.1.3) constitute viable practical approaches for the effective contro] of both the black

smoke and the SO emissions Exhaust after treatment is an addi-

tional possibility offered, especially for larger vehicles, by

emerging technologies, such as smoke traps or smoke oxidizers These however are not yet sufficiently proven in large-scale ap-

plications

Light duty diesel-powered vehicles constitute normally a small

fraction of the light duty vehicle fleet Yet, they may be signif-

icant contributors to the urban black smoke and SQp problems as

they are often preferred for professional use (@.g as taxis)

Their annual milage tends thus to be high, while their emissions

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where the air pollution problem is worst The emission control op-

tions are the same as for heavy duty vehicles, i.e., I/M, better

Diesel quality and renewal of the aging fleet with modern low emissions vehicles

The choice of appropriate low emission technologies for new Diesel powered cars can be promulgated through appropriate standards that

define the state of the art of diesel engine design Imposition of reasonably strict standards is beneficial from the environmental

point of view, as it prevents vehicles with unduly high emissions

from being put into circulation, and does not have any major nega-

tive economic repercussions The last may not be true in certain cases, as for example when diesel engines are locally produced, and strict standards may adversely affect the competitiveness of relevant industries

Based on the above, the issue of imposing reasonably strict stan-

dards for diesel powered engines appears not to be a particularly controversial one in most cases Table 8.1,3.2.1-1 below lists relevant standards from the European Community, for the purpose of providing some guidance on the level of emissions that the vehicle industry can meet Indeed, EC standards tend so far to follow closely the technological progress made by the car manufacturing segment, rather than to lead and accelerate it, and as such they may be considered to represent practical levels, which may be

suitable also for developing nations It should be kept in mind

that emission standards depend on the test cycle used and that they should be periodically modified to reflect the progress made

in the engine design

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Photochemical pollution has emerged over the past couple of decades as the major problem in many large urban centres, and LDGP vehicles play a

key role in its formation The choice of control technologies to be

promoted for new LDGP cars, which replace old ones and add to the

expanding fleet, constitute thus an important decision with far reaching environmental implications, but also with significant economic and

energy impacts

Control af the exhaust emissions from new vehicles through catalytic converters offers the important advantage of low emissions There are

however a number of prerequisites for the successful operation of such

technologies, as well as important cost considerations, which should not be ignored:

(a) Successful I/M programmes are required for ensuring that the cat-

alytic systems continue to function properly during the entire

vehicle life;

The average retirement age of catalytic vehicles should not exceed that in developed countries, since the good condition of the engine, up to the retirement point, is a prerequisite for the

proper function of the catalyst;

The engine of a catalytic car has to be larger than that of a similar conventional car for comparable performance (e.g 1400 cc

instead of 1200 cc);

Larger engines, as well as engine operating constraints imposed by catalytic systems, make catalytic vehicles with their catalysts removed or destroyed considerably "dirtier" than modern con-

ventional cars designed to minimize the generation of emissions For the same reasons catalytic cars have higher fuel consumption; Unleaded gasoline must be made widely available and effective measures to prevent its contamination with leaded gasolines should be instituted (the lead in gasoline poisons and destroys the cata-

lyst)

Catalytic technologies constitute at present a key measure for the abatement of photochemical pollution and their usefulness in developed nations is well established Developing nations should probably weigh carefully the emission reduction advantages from the successful use of

the catalytic technologies against the potential environmental problems from the failure of such systems to perform as intended under local

conditions (e.g due to lack of infrastructure for establishing and maintaining effective I/M programmes, or due to economic constraints in- hibiting the timely replacement of aging catalytic vehicles) They should also analyse carefully the direct and indirect cost elements associated with this measure (e.g costs and benefits due to the possible

shortened useful life of cars, costs due to the purchase of cars

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Alternative solutions to the photochemical pollution problem may exist

and should be examined along with the above economic and environmental considerations For example, a strategy promoting conventional smaT1- size vehicles with reasonably low emissions, a fast reorganization and

radical upgrading of the mass transport system, as well as a possible streamlining of the city functions may be several times more cost-effective, from the national economy point of view, than the sole reliance on

the catalytic technology solution On the other hand, if the number and use of conventional cars is expected to grow significantly, conventional

technologies alone may not be able to offer an adequate solution over a period that extends over the life span of the new cars In the latter case the available resources might have to be allocated in an optimum

way in both directions

From the preceding discussion it would appear that catalytic technologies for LDGP cars are appropriate for developed economies with a high standard of living and good infrastructure For developing regions however, they do not necessarily represent the highest priority

approach They do however become necessary at some point along the

development path, as the size of cities grows and the number of private

cars increases, but only after all simpler and more cost effective

methods are exhausted Vehicle technologies are often promulgated through the choice of the ap-

plicable exhaust emission standards Indeed, if the emission standards are sufficiently strict, 3-way controlled catalysts have to be used More relaxed standards may for example dictate the use of 3-way controlled catalysts for larger size vehicles (engines > 1400 cc), while

allowing conventional technologies for smaller size vehicles (engines < 1400 cc) with good engine design The imposition of sufficiently strict

standards is valuable, even if cars with conventional technologies are

to be used, as it restricts vehicles with higher than normal emissions from being put into circulation

Table 8,1.3.2.1-2 below lists the previous and the present European Com- munity (EC) standards for LDGP cars The ECE 15-05 standard is of

intermediate severity as it allows conventional engines of good design for small size vehicles (engines < 1400 cc) The current ones make the

use of 3-way controlled catalytic technologies mandatory for all LDGP

car sizes As in the case of diesel powered vehicles, it should be kept

in mind that emission standards depend on the test cycle used The Tatter has been modified in EC and, while the ECE 15-05 standards, were

based on a test cycle with an average speed of 19.6 km/h, the current

ones, 91/441/EEC, are based on a test cycle with an average speed of 33.6 km/h

Control of evaporative emissions becomes increasingly important as the

exhaust emissions from modern vehicles are progressively reduced and their uncontrolled evaporative emissions emerge as the dominant source of VOC The relevant technologies are relatively simple, and the adop- tion of appropriate standards constitutes a cost-effective measure of

fairly high priority for the abatement of photochemical pollution

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Table 8.1.3.2.1-2 Past and Present European Community Emission Stan- dards for LDGP Cars

ÿ0 N0x+VÖC NOx Effective Date

gr/kin gr/km New/Existing Models ECE 15-05 Type Approval Engine <1400cc Engine 1400-2000cc Engine >2000cc Conformity of Production Engine <1400cc Engine 1400-2000cc Engine >2000cc 91/441/EEC Type approval ? Conformity of Production 3

8.1.3.2.2 Control Systems for Industrial Sources

The model in Section 3.2.2 lists most of the established control systems for each type of industrial source and assesses the impact of their use As discussed in Section 8.1.2.2, the choice of the minimum treatment re-

quired for individual large sources can be derived from the critical

short-term impact analysis, while that for multiple smal] sources could be derived from annual or seasonal impact analysis Moreover, photochem-

ical pollution control consideration may dictate a range of measures for the reduction of VOC and/or NO, emissions from large and small sources If priorities are to be set for achieving a certain degree of emission

reduction (e.g in the VOC or the TSP emissions), the most cost/effective control measures (on the basis of cost/kg of pollutant removed) are normally these associated with the larger sources and with the primary control systems (e.g cyclones)

8.1.3.3 Reduction of the Emissions Impact on Air Quality

Emissions can be reduced through controls at the source (see Section

8.1.3.1) and/or through the use of control systems (see Section

8.1.3.2) Yet, in most cases, some polluting loads have to be released into the atmosphere, and our Tast line of defense is to ensure, through

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appropriate release conditions, that such emissions do not violate the

applicable air quality guidelines or standards

The critical short term impact analysis can be applied as discussed in Sections 8.1.2.2 and 8.2.1 to assess whether the impact from any given point source is acceptable and, if not, to determine the necessary mitigation options These options include the restriction of emissions through reduction at the source techniques (see Section 8.1.3.1) or through contro] measures (see Section 8.1.3.2) and the level of the required reductions can easily be determined through the critical impact analysis procedure described in Section 8.2.1 Instead and/or in paral-

Jel with the above technical measures, the impact of emissions can be reduced through appropriate modification of the emission released conditions so as to prevent violation of the applicable ambient air quality guidelines or standards Such modifications include the increase in the

physical height of the stack, and/or the compounding of exhaust gases from adjacent sources into single stacks, and/or modifications in the exit gas volumes, temperatures or velocities The impact of any such

modification, as well as the combined impact of any set of relevant modifications can be quickly and easily assessed through the air quality models of Section 8.2.1

Based on the above, the critical impact analysis procedure allows the

determination of conditions that prevent the violation of the applicable

short term air quality standards Under such conditions long term standards are unlikely to be violated as well, Section 8.1.2.1 In addition to this, the long term (seasonal or annual) impact analysis procedures,

described in Section 8.2.2.2, can be used in certain cases for assessing and minimizing the long term impact of point sources on selected

sensitive receptors, such as ancient monuments, hospitals, or densely populated areas already burdened with high pollution levels from other

sources Moreover, in the case of a new source, one could investigate

the suitability of alternative locations in relation to the prevailing meteorological conditions, having as an objective to minimize the annual average pollutant concentrations on selected sensitive receptor(s) 8.1.3.4 Institutional Measures

This category comprises measures, some of which are not sufficiently ap- preciated, and hence are often not considered in air pollution contro]

strategies Yet their potential impacts, positive as well as negative if

the situation remains uncontrolled, can be very significant Most of these measures are also associated with improved quality of urban life and with very significant economic benefits as well

Prominent among these measures, both from the environmental and the economic point of view, is the management of the vehicle kilometers trav-

elled, mainly through improved public transportation and possibly

through subsidized fares, but also through other measures such as incentives for car pooling, selective restrictions for parking or traffic,

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as its continuing deterioration often compensates the positive impacts

of any control strategy Depending on the local conditions, the impor-

tance of other institutional measures, such as the relocation of spe-

cific industrial processes and the modification of the spatial and temporal distribution of emissions, may prove necessary or even cost- effective

8.1.3.4.1 Management of Vehicle Kilometers Travelled

Increasing urbanization and standard of living results in ever increasing numbers of private vehicles in urban areas The situation becomes critical as most cities are not designed to accommodate such large numbers of vehicles from both the parking and the circulation point of

view Still worse, the trend in most developing countries is Tikely to

continue, and even accelerate, with detrimental effects on the quality

of urban air and life If the growing need for urban transportation is allowed to be satisfied through the use of private cars, the negative impact on the national economy, as well as on the environment and the

quality of urban life, can be very serious The normalized cost and

emission loads per passenger-kilometer travelled which are high in the case of vehicles with a single passenger, are reduced as the number of passengers per vehicle increases through car pooling, and are minimized through the use of mass transport media

Unfortunately, the increase in urban traffic is not related linearly to

the pollution loads released Indeed, higher traffic causes on one hand

increased numbers of vehicle-kilometers in the study area, and on the

other hand Towering of the average vehicle speeds As the exhaust emissions model of Section 3.3 shows, if the average speed drops below about

25 km/h, the ensuing increase in the emission factors is exponential Thus, the increasing vehicle-kilometers in the study area have to be

multiplied by the exponentially increasing emission factors to yield the

annual emission loads

Public transportation represents an extremely cost-effective measure to reduce the mileage of private cars in urban areas and to maintain acceptable traffic and environmental conditions In fact, the urban traffic situation represents, at any time, the established equilibrium between the convenience, speed and cost associated with mass versus private transportation systems If the former is not in a position to compete effectively with the latter, the urban traffic is 1ikely to get out of control forcing the public to buy more cars, while promoting ever increasing use of existing private vehicles Billions of productive man hours can be lost annually in traffic jams, while the cost to the national economy of the inflated size and increased use of the private car fleet can be overwhelming In order to solve the associated air pollution problems "cleaner" catalytic cars can be introduced, better

road infrastructure can be created, and the mass transportation system

can be improved Unfortunately, the emphasis is often on the first two,

despite the fact that radical improvement of the mass transportation system can be a far more cost-effective and environmentally safer

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solution, and is a prerequisite for most large urban areas in the

developing world

Organization of public transportation can start from relatively simple and fast to implement measures, such as the optimization of the bus routing and transfer system, the allocation of exclusive secondary roads and/or lanes for the use of buses or trolleys, the assignment of the

right of way to mass transportation vehicles, etc., and can continue un-

til a modern and fully developed system exists It is important that relevant plans are complete (so as to have clear targets and ensure that all measures are compatible) and organized into short, medium and long term phases (so as to have the simple and fast-to-implement measures

clearly distinguished from the more complex and time consuming ones, and

all of them executed in a proper sequence for smooth transition)

Additional measures, such as government subsidies for the mass transportation system so as to reduce fares, elimination of downtown parking for non residents, selective restrictions on the traffic flow towards the city centre, levying of fees for vehicles accessing central congested areas, etc., could discourage the use of private cars and promote decisively the use of public transportation

Measures aimed at making private transport more effective have been

tried in some countries with success Carpooling is an obvious way to achieve this goal and policies promoting this measure include high occupancy vehicle Janes for buses and/or carpools

Assessment of the impact of the relevant measures in terms of reduced

emissions or improved air quality is difficult, as the response of the

public and the ensuing changes in traffic conditions cannot be predicted

accurately The study team could however, with the assistance of experienced traffic engineers, formulate alternative action programmes

and through engineering judgement assess their impact on the traffic conditions The emission load model of Section 3.3, and possibly the air

quality model of 8.2.2.3, can then be used to predict the environmental effectiveness of such programmes This simple screening exercise may reveal significant sensitivities and may help to set targets for further detailed evaluations

8.1.3.4.2 Relocation of Industrial Sources

In many urban areas, industries once located at the outskirts or outside the city limits, and up surrounded by residential areas as the city ex- pands Through proper land pianning and controls this often unavoidable process may not be entirely objectionable as, among other things, it tends to minimize the transportation of personnel and products

There are cases however, where large plants with significant and difficult to control sources (e.g fugitive sources) or with processes posing significant risk for major accidental releases (e.g plants having pres-

surized ammonia storage tanks or pesticides compounding operations) end

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small operations, such as grey iron foundries, with emissions that are difficult to control mainly due to their small size and primitive

installations, may also operate within residential areas

Relocation of the above industrial sources to proper locations may be a

reasonable target, but has to be planned carefully and implemented through proper incentives, preferably combined with production compound-

ing and modernization This may be simpler and less expensive for the

small sources that create local problems, while for larger plants it may have to be worked out through careful prioritization, so as to have only specific processes with significant emissions and/or risk of accidental

releases relocated

In general the relocation of industrial sources is a very expensive

proposition and affects the economy of the local communities For this reason it should be viewed as a last resort measure and exerted with great moderation Proper long term planning and adequate incentives may

be employed to gradually improve the existing situation

8.1.3.4.3 Temporal Distribution of Area and Point Source Emissions

A number of institutional measures can be used to alleviate the traffic congestion problems encountered at specific hours of the day For exam-

ple, flexible working hours for offices tends to reduce the early morning traffic peaks Fixed shopping hours on the other hand tends to create severe traffic peaks, often at unfavourable hours from the pollutant

dispersion point of view

Daylight Saving Time during the summer may, in certain areas, have an

adverse effect on photochemical poljution as it shifts the morning

traffic one hour earlier at times where low temperature inversions may

still persist This may accumulate higher initial primary pollutant concentrations, while it provides more time for the photochemical reactions to be completed Proper assessment however, can only be made with the use of a photochemical model and local meteorological data

Control of the starting time for the morning shift of selected large industrial sources in urban areas, may be employed so as to shift their

emissions towards late morning and early afternoon hours, where the mix-

ing layer has the maximum height This tends to reduce both the short and long term environmental impact from their emissions On a short term basis this may mean a much reduced probability of occurrence of the critical concentrations predicted by the models of Section 8.2.1 For assessment of the long term impact and for the justification of relevant

measures appropriate computer models with local meteorological data should be used

In relation to area sources, simple and effective measures that affect their temporal emissions sometimes exist For example, in a study area the prevailing operation of central heating furnaces was from about 05:00 to 07:00 and from about 18:00 to 21:00 hours, designed to offer

maximum comfort to tenants in the morning, prior to their departure for

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work, as well as during the evening family life hours During these times however, the atmospheric conditions tend to be stable and low

level temperature inversions prevail As a result, the impact from the

space heating emissions is elevated If temperature feedback control

rather than timers were used for regulating the boiler operation, the

relevant temporal shift of the space heating emissions could result in significantly lower long- and short-term environmental impacts The model in Section 8.2.2.3 could be used for evaluating the impact on the former

In relation to large industrial sources other simple and highly effective measures may sometimes be possible For example, a large residue oil fired power plant was operating in the coastal area at the outskirts of a metropolitan area The residue oil received had a maximum sulfur content of 0.7 %, but its actual content was highly variable ranging

from 0.1 to 0.7 % Storing the low sulfur oi] in a separate tank and

using it at periods when the wind direction was towards the city could

have been a low cost, yet highly effective, measure to reduce the SQe

impact on the inhabited areas In addition, modification of the regular night-time soot blowing schedule, aimed at cleaning the heat transfer

tubes from the accumulated particles, and allowing it only at times when

the wind blew away from the city and towards the sea, could have

eliminated the worst irritation to near-by residents These and other

necessary measures were not taken in time, and a political decision was made to have the plant closed down

8.1.3.4.4 Management of the Population and Traffic Densities

High population densities are closely associated with high emission den-

sities from traffic, space heating and related services If one could

derive a compounded emission factor per capita, the model in Section 8.2.2.3 could be used for calculating the limiting population densities, as a function of the city size and in relation to the prevailing

meteorological conditions, so as to maintain an acceptable level of non reactive potlutants

In situations where high population and traffic densities already pre-

vail it is often a mistake to assume that the situation is out of control and little could be done about it Experience shows that negative environmental impacts from the continuing population growth and traffic

density deterioration can cancel out the positive impact of any control strategy by the time the latter is implemented or shortly thereafter Regulations Jimiting the allowable floor area of new buildings while imposing the creation of adequate parking places for the building tenants and visitors go a long way towards decelerating the deterioration in highly congested areas In addition, balanced economic restraints could be used to discourage and regulate the ownership and use of private cars In any case all restraints should be accompanied by the provision of alternative solutions for the population For example the discourage-

ment of car ownership and use should be accompanied by the provision of

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8-39

Management of Air Pallution

a truly effective public transportation system, for otherwise the

measures become repressive and tend to be circumvented

Improvement of traffic flow through street modifications, signalization, or banning the circulation of certain categories of vehicles in highly congested areas (e.g 50 % reduction operated on the basis of odd or even numbers of vehicle registration) are some of the measures that

could be used to alleviate traffic conditions within a short time and at relatively low cost Traffic restrictions however, if applied over wide

areas, may adversely affect local residents and contribute to the

increase in the number of private cars, may create traffic congestions in other areas and almost inevitably result in increased total vehicle-

kilometers

Other important measures are related to the organization of the city in a way that minimizes the commuting needs For example, the development

of multiple commercial centres in large urban areas tends to attenuate crowding in the city centre and reduce travelling distances Moreover,

organization of the public and private sector in the direction of restricting bureaucracy may prove extremely effective both, from the economic, as well as from the pollution control point of view Indeed,

an often larger than anticipated fraction of the commuting, especially in central congested areas of large urban centres, is directly at- tributed to the bureaucracy of key government and private services

(ministries, banks, etc) and this could, in principle, be easily reduced

In conclusion, most large urban areas have developed from older patterns and/or without adequate proper planning Through this process the considerable infrastructure requirements of traffic, as well as the con- sequences of the intensified energy use of modern life, have been ignored, This is in fact the root of most urban air pollution problems, as well as of the quality of life deterioration Technical measures alone are costly and do not offer satisfactory environmental solutions, unless

the basic causes of the problem are confronted first in innovative, and

perhaps politically daring, ways

8.1.4 Synthesis of Rational Urban Air Pollution Control Strategies

In Section 8.1.1 the available emission inventory and air quality models were reviewed Section 8.1.2 focused on the use of air quality models for the analysis of the existing situation and for the evaluation of the impact of alternative control measures In Section 8.1.3 many of the alternative control options were considered, their implementation prob-

lems and schemes were discussed and possible interrelationships exam-

ined The subject of the this section is how ane can use the available

tools to synthesize effective, enforceable and near optimum strategies

for the study area under consideration

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categories: the short and long term problems from relatively stable pollutants, and the photochemical pollution problems A brief discussion

of how one can deal with each of the these categories is given in the

sections that follow

8.1.4.1 Short Term Air Pollution Problems

Assuming that the area sources are controlled so as to have the long

term standards met, the short term air pollution problems are likely to

be caused by the point sources and are of local significance (see Sec- tion 8.1.2)

For the abatement of the such problems there are a number of options

available These options include the restriction of emissions through

reduction at the source techniques (see Section 8.1.1) or through control measures (see Section 8.1.2), as well as the reduction of the emissions impact through appropriate modification of the emission released conditions so as to prevent violation of the applicable ambient air quality standards Such modifications include increase of the physical stack height, and/or compounding of exhaust gases from adjacent sources

into a single stack, and/or modifications in the exit gas volumes, tem-

peratures or velocities (see Section 8.1.3.3)

The impact of control measures in the reduction of emission Toads can be estimated through the inventory model of Section 3.2 The critical short term impact analysis procedure can be carried out, on a source by source

basis, as described in Sections 8.1.2.2 and 8.2.1, for assessing whether

the impact from each selected point source is acceptable or not, and in the latter case for determining the necessary mitigation options

As an example, for the contro? of short-term S09 problems from the residue oi] fired industrial boilers of a study area, the critical

impact analysis procedure of Section 8.2.1.1.3 was followed, and the results are summarized in Tables 8.1.2.2.1-1 and 8.1.2.2.1-2 of Section 8.1.2.2.1

From the analysis of the existing situation it can be seen that in several cases the hourly S02 standard of 350 ug/m? could be severely violated The mitigation options considered in this case were the improvement of the residue oil quality by reducing its sulfur content from it present level of 3.5 % and the increase of the stack heights

The maximum allowable sulfur content and, alternatively, the minimum physical stack height for each source were computed and the results are listed in Tables 8.1.2.2.1-1 and 8.1.2.2.1-2 The

sulfur content was eventually reduced to 0.7 % from 3.5 % and this

was sufficient to safeguard against violations of the 350 ug/m

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