Ambient Air Quality and Continuous Emissions Monitoring 6.1 AMBIENT AIR QUALITY SAMPLING PROGRAM Air pollution monitoring is conducted to determine either emission concentration or ambient air quality. The range of emission concentrations, temperature, and pressures encountered is sometimes many magnitudes greater than found at an ambient air sampling station. For this reason, sampling and analysis techniques and equipment are different for each case, even though the same general principles may be employed. This chapter deals with both ambient air quality sampling procedures and monitoring and continuous emissions monitoring. Lodge 1 presents a good dis- cussion in Methods of Air Sampling and Analysis. 6.2 OBJECTIVES OF A SAMPLING PROGRAM Instrumentation for ambient air quality monitoring is perhaps best described in terms of the types of measurements that would be made in a typical community by the local air pollution control agency. Usually a sample network would be installed that would blanket the area with a series of similar stations. The object would be to measure the amount of gaseous and particulate matter at enough locations to make the data statistically significant. It is not uncommon to find each station in a network equipped with simple, unsophisticated grab sampling devices. However, quite a few sophisticated monitoring networks have been developed which contain continuous monitors with telemetry and computer control. Meteorological variables are also monitored and correlated with the concentration data. The information is then used: 1. To establish and evaluate control measures 2. To evaluate atmospheric-diffusion model parameters 3. To determine areas and time periods when hazardous levels of pollution exist in the atmosphere 4. For emergency warning systems 6.3 MONITORING SYSTEMS Ambient air quality data may be obtained through the use of mobile or fixed sampling networks and the use of integrated samplers or continuous monitors. Decisions 6 9588ch06 frame Page 67 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC regarding these monitoring techniques constitute the first important steps in design of a monitoring network. 6.3.1 F IXED VS . M OBILE S AMPLING Fixed-point sampling entails a network of monitoring stations at selected sites, operated simultaneously throughout the study. Stations are permanent or, at least, long-term installations. In a mobile sampling network, the monitoring/sampling instruments are rotated on schedule among selected locations. The monitoring/sam- pling is not conducted simultaneously at all locations, and the equipment is generally housed in trailers, automobiles, or other mobile units. An advantage of fixed sampling is that measurements are made concurrently at all sites, providing directly compa- rable information, which is particularly important in determining relationship of polluting sources to local air quality and in tracing dispersion of pollutants through- out the area. The chief advantage of mobile sampling is that air quality measurements can be made at many sites — far more than would be feasible in a fixed sampling program. Mobile sampling provides better definition of the geographical variations if the program is long enough to generate meaningful data. 6.3.2 C ONTINUOUS VS . I NTEGRATED S AMPLING Continuous monitoring is conducted with devices that operate as both sampler and analyzer. Pollutant concentrations are instantaneously displayed on a meter, contin- uously recorded on a chart, magnetic tape, or disk. Integrated sampling is done with devices that collect a sample over some specified time interval after which the sample is sent to a laboratory for analysis. The result is a single pollutant concentration that has been integrated, or averaged, over the entire sampling period. This is an older technique and currently in limited use. Continuous or automatic monitoring instruments offer some advantages over integrating samplers; for example, there is a capability for furnishing short-interval data, and there is a rapid availability of data. Moreover, output of the instruments can be electronically sent to a central point. Also, continuous monitors require less laboratory support. They also may be necessary to monitor some pollutants where no integrating method is available or where it is necessary to collect data over short averaging times, for example, 15 min. Automated monitors also have some draw- backs. They require more sophisticated maintenance and calibration, and the oper- ators and maintenance personnel have to be more highly technically trained. The selection of a monitoring system is influenced by the averaging time for which concentrations are desired, i.e., 15-min, 1-h, 3-h, 8-h, 12-h, or 24-h time intervals. It should be consistent with the averaging times specified by air quality standards. For example, in assessing SO 2 levels, good coverage can be provided by use of integrated samples, widely dispersed over the area, and one or more contin- uous sampler/analyzers situated in heavily populated areas. The integrated sampler defines SO 2 levels over a broad area, and the continuous devices provide detailed information on diurnal patterns. The short averaging time of interest for CO and ozone dictates the use of continuous monitors for these pollutants. 9588ch06 frame Page 68 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC 6.3.3 S ELECTION OF I NSTRUMENTATION AND M ETHODS Choice of instrumentation for an air-monitoring network depends on the following factors: • Type of pollutants • Averaging time specified by air quality criteria or standards • Expected pollutant levels • Available resources • Availability of trained personnel • Presence in the air of interfering materials Most pollutants may be monitored by a number of different methods and tech- niques. The selection of the methodology to be used is an important step in the design of the monitoring portion of the assessment study. 6.4 FEDERAL REFERENCE METHODS AND CONTINUOUS MONITORING In order to evaluate the current air quality and the effect of air pollution control measures, most larger communities maintain monitoring networks. The EPA, as well as most of the states, maintains its own surveillance networks. The ideal objective when installing a monitoring network is to be able to obtain continuous real time data. Table 6.1 lists standard methods of measurement. Only 3 of these standard methods employ continuous or semicontinuous monitors. No satisfactory device exists as yet for determining suspended particulate on a continuous basis. However, Table 6.2 lists continuous methods which are now com- monly employed for the measurement of the five regulated air pollutants. TABLE 6.1 Federal Reference Methods Pollutant Collection Method Analysis Sulfur dioxide Absorption in bubbler Spectrophotochemically Particulate matter Filtration in hi-volume sampler Gravimetrically Carbon monoxide Continuous NDIR monitor Absorption of infrared energy Nitrogen dioxide Continuous monitor Chemiluminescence reaction with ozone Hydrocarbons Semi-continuous monitor Chromatographic separation with flame ionization detector Ozone Continuous monitor Chemiluminescence reaction with ethylene Lead Filtration in hi-volume sampler Extracted by acid, atomic absorption spectrometry 9588ch06 frame Page 69 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC Particulate matter emissions can be continuously detected through opacity mea- surements. Opacity is a function of light transmission through the plume and is define by the following equation (6.1) where OP = percent opacity I = light flux leaving the plume I 0 = incident light flux The following information, Documentation of the Federal Reference Methods for the Determination of the Regulated Air Pollutants, can be found in the Code of Federal Regulations , Title 40 (CFR 40) — Protection of Environment , Chapter 1, Environmental Protection Agency, Subchapter C — Air Programs, Part 50, National Primary and Secondary Ambient Air Quality Standards. The following is a list of those methods with reference to CFR 40. TABLE 6.2 Continuous Monitor Methods for Federally Regulated Pollutants Pollutant Continuous Monitor Method Sulfur dioxide Conductrometric Coulometric Flame chemiluminescence Carbon monoxide Non-dispersive infrared or gas chromatograph, with conversion to methane, flame ionization detection, a semicontinuous method Nitrogen dioxide Coulometric Chemiluminescent reaction with ozone Hydrocarbons Gas chromatograph Flame ionization detector Semicontinuous Ozone Coulometric Chemiluminescent reaction with ethylene Documentation of the Federal Reference Methods for the Determination of Regulated Air Pollutants Sulfur Dioxide Appendix A Reference Method for the Determination of Sulfur Dioxide in the Atmosphere (Pararosaniline Method) Particulate Matter Appendix B Reference Method for the Determination of Suspended Particulate in the Atmosphere — High Volume Method (Total suspended particulate has been replaced by PM 10 and PM 2.5 .) OP I I=− () ×1 100 0 9588ch06 frame Page 70 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC 6.5 THE “COMPLETE” ENVIRONMENTAL SURVEILLANCE AND CONTROL SYSTEM An ideal surveillance and control system can be devised employing continuous monitoring, telemetering, and electronic data processing. It is possible to assemble such a system from the hardware components that are now available. The major drawback of this automatic system is the limitations of the computer software; there is little economic information available for formulating the ambient air quality and optimizing models. Figure 6.1 illustrates one conception of a surveillance and control system. This system would demand instruments which could be calibrated to a known standard, would retain their calibration over long periods of time, would be Carbon Monoxide Appendix C Measurement Principle and Calibration Procedure for the Continuous Measurement of Carbon Monoxide in the Atmosphere (Non-Dispersive Infrared Spectrometry) Ozone Appendix D Measurement Principle and Calibration Procedure for the Measurement of Photochemical Oxidants Corrected for Interferences Due to Nitrogen Oxides and Sulfur Dioxide Hydrocarbons Appendix E (Corrected for Methane) Reference Method for Determination of Hydrocarbons Corrected for Methane Nitrogen Dioxide Appendix F Measurement Principle and Calibration Procedure for the Measurement of Nitrogen Dioxide in the Atmosphere (Gas Phase Chemiluminescence) Lead Appendix G Reference Method for the Determination of Lead in Suspended Particulate Matter Collected from Ambient Air Ozone Appendix H Interpretation of the National Ambient Air Quality Standards for Ozone PM 10 Appendix J Reference Method for the Determination of Particulate Matter as PM 10 in the Atmosphere Particulate Matter Appendix K Interpretation of the National Ambient Air Quality Standards for Particulate Matter (Includes PM 2.5 ) 9588ch06 frame Page 71 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC free of electronic drift over these long-time periods, and would possess suitable dynamic response. Many automated environmental surveillance systems employing continuous monitors exist in the U.S. and throughout the world. None are quite as sophisticated as would be implied by the system of Figure 6.1. FIGURE 6.1 Conception of a surveillance and control system. 9588ch06 frame Page 72 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC 6.6 TYPICAL AIR SAMPLING TRAIN A typical air pollution sampling train is applicable to the intermittent collection of an air sample containing either gaseous or particulate pollutants. The sample is retained in the collection equipment which is then removed for the sample train. Further processing takes place to prepare the sample for analysis. Most of the analysis techniques are standard procedures involving one or more of the following methods: 1. Gravimetric 2. Volumetric 3. Microscopy 4. Instrumental a. Spectrophotometric i. Ultraviolet ii. Visible (Colorimetry) iii. Infra-red b. Electrical i. Conductometric ii. Coulometric iii. Titrimetric c. Emission Spectroscopy d. Mass Spectroscopy e. Chromatography 6.7 INTEGRATED SAMPLING DEVICES FOR SUSPENDED PARTICULATE MATTER Suspended particulate are small particulate that vary in size from less than 1 micron to approximately 100 microns. They remain suspended in the atmosphere for long periods of time and absorb, reflect, and scatter the sunlight, obscuring visibility. When breathed, they penetrate deeply into the lungs. They also cause economic loss because of their soiling and corrosive properties. The new EPA ambient particulate-matter definition includes only the part of the size distribution that could penetrate into the human thorax. This requires a sampling inlet with a 10 µ m cutpoint to mimic deposition in the extra thoracic regions. Figure 6.2 is a schematic of a sampler designed to meet this requirement. There is a two-stage selective inlet. Air is drawn into the inlet and deflected downward into acceleration jets of the first-stage fractionator. Larger, non-inhalable particles are removed. Air then flows through the first stage vent tubes and then through the second fractionation stage. More non-inhalable particles are removed, and the remaining aerosol is drawn through the usual 8 ″ × 10 ″ sampling filter. The new PM 10 standard includes only those particles with an aerodynamic diameter less than or equal to 10 µ m. This standard went into effect on July 31, 1987. 9588ch06 frame Page 73 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC 6.8 CONTINUOUS AIR QUALITY MONITORS Continuous emissions monitoring (CEM) is required by the Clean Air Act Amend- ments to monitor SO 2 , NO x , CO, CO 2 , opacity, total hydrocarbons, and total reduced sulfur (TRS). Title IV, which is to ensure compliance with the Acid Rain Program, sets out provisions for CEM in the two-phase utility power industry control strategy. Phase I Utilities were required to install CEM by November 15, 1993, and Phase II Utilities by January 1, 1995. Title III focuses on 189 hazardous air pollutants (HAP), some of which will possibly require CEM. This should spawn CEM techniques optimized for the chemical compound being monitored. Title V will require CEM for compliance assurance. The collection of real-time emission data will be the first step to attaining the national mandated reduction in SO 2 and NO x emissions. Fur- thermore, CEM can be used to track use of allowances in the new market-based SO 2 emissions trading program. CEM is carried out by two general methods — in situ and extractive. Each of the methods measures on a volumetric basis, ppm for example. Therefore, the measurements require conversion to mass emission rates on a lb/h or lb/10 6 BTU basis. Monitoring instrumentation requires at least 10% relative accuracy. Perfor- mance specifications and test procedures can be found in Title 40 CFR, Part 60, Appendix B. FIGURE 6.2 Two-stage particulate sampler. 9588ch06 frame Page 74 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC The EPA Emission Measurement Center (EMC) at Research Triangle Park and the Midwest Research Institute have created a data base on CEM. You may use browse techniques or search the data base by HAP or analyzer type. The data base is found on the EPA home page at: www.epa.gov/ttnami1/siteindx.html. Figure 6.3 is a schematic flow diagram of a general continuous air-quality mon- itor. The device contains: 1. Primary air-moving device, usually a vacuum pump, to pull the air sample through the instrument 2. Flow-control and -monitoring device, usually a constant pressure regulator and rotameter 3. Pollutant detection by various primary sensing techniques 4. Automatic reagent addition where needed 5. Electronic circuitry for transducing the primary signal to a signal suitable for recording and telemetering 6. Provisions for automatic calibration, usually several solenoid valves which can be operated remotely to connect the inlet gas to a scrubbing train for removal of all pollutants and establishing a chemical zero, or, alternatively, to one or more span gases for setting the chemical range of the instruments. Many monitors of the general type described above have been developed for all of the federally regulated gaseous pollutants and others as well. The remainder of this section will provide details of these devices. This list is not exhaustive. Further- more, although the devices described below are indicated for a particular pollutant, they can be used for other types of pollutants as well. 6.8.1 E LECTROCONDUCTIVITY A NALYZER FOR SO 2 Electrical conductivity was the basis of the first continuous monitor used to detect and monitor an air pollutant — SO 2 . This monitor was built by a Dr. Thomas to monitor SO 2 in a greenhouse during a study of the effects of SO 2 on plants. Later, it was employed by TVA in its original studies of SO 2 from power plant plumes. In an electroconductivity apparatus, a reagent passes through a reference con- ductivity cell and then into an absorbing column. Air is drawn by a vacuum pump counter-currently to the reagent flow through the absorbing tube, then through a separator to the exhaust. The SO 2 is absorbed in the reagent which then passes through a measuring conductivity cell. A stabilized AC voltage is impressed across the conductivity cells resulting in a current flow that is directly proportional to the conductivity of the solution. The value of this current is measured by connecting a resistor in series with the cell to obtain an AC voltage which is proportional to the current. This voltage is then rectified to direct current. The DC signals from the rectifiers are connected in opposition, thus resulting in a voltage that induces a current through a meter which is directly related to the difference in conductivity between the two solutions. To set the zero on the instrument, any SO 2 is removed by passing the air through a soda-lime absorber. The conductivity in both cells should then be the same, and the meter output should be zero. 9588ch06 frame Page 75 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC FIGURE 6.3 Generalized automatic continuous air pollution monitor. 9588ch06 frame Page 76 Wednesday, September 5, 2001 9:46 PM © 2002 by CRC Press LLC © 2002 by CRC Press LLC [...]... nitric oxide then using the ozone reaction 6. 8.8 CALIBRATION OF CONTINUOUS MONITORS 6. 8.8.1 Specifications for Continuous Air- Quality Monitors It is unfortunate that terms used in specifying and calibrating air- monitoring instrumentation are sometimes ambiguous Thus we find the term “dynamic” dilution being used to mean diluting a flowing gas stream under carefully controlled constant flow conditions to produce... definition, steady-state specification, dynamic specification, or ambient specification 6. 8.8.2 Steady-State Calibrations One of the most difficult problems encountered in calibrating air pollution instrumentation is the production of low-level concentrations which are in the range encountered in the atmosphere There are several suppliers of gas cylinders with prepared and certified low-level gas concentrations... crystal-controlled radio-frequency oscillator Additional electronic circuitry in the oscillator unit demodulates and filters the resultant signal, yielding a 10 Hz signal The 10 Hz signal is routed to the amplifier /control section for amplification and phase inversion, then back into the analyzer section for synchronous rectification The resulting fullwave-rectified signal is returned to the amplifier /control. .. 6. 8.2 COULOMETRIC ANALYZER FOR SO2 Principle of operation of a coulometric analyzer is similar to an electroconductivity apparatus, except three electrodes are required One is a reference electrode Figure 6. 4 shows the three-electrode circuit An air sample is drawn through a detector cell which contains a buffered solution of KI Then iodine, I2, is generated at the anode, 2I − → I 2 + 2e − FIGURE 6. 4... conditioning, as required, to drive the meter and recorder © 2002 by CRC Press LLC 9588ch 06 frame Page 80 Wednesday, September 5, 2001 9: 46 PM 6. 8.4 FLAME PHOTOMETRIC DETECTION OF TOTAL SULFUR AND SO2 Sulfur compounds introduced into a hydrogen-rich flame produce strong luminescent emissions between 300 and 423 nm A narrow-band optical filter placed between the flame and detector permits transmission at 394... Cis-butene-2 which the tube is subjected The basic determiDimethyl sulfide Trans butene-2 nation of permeation rate can be made graviDimethyl disulfide Ethylene oxide metrically; thus, a permeation tube can become Methyl mercaptan Others a true standard Table 6. 3 lists some of the gases for which permeation tubes are available Tubes of proper length can be used to calibrate gas analyzers at a steady-state... spheres, and the rate of reaction was determined to be proportional to the number © 2002 by CRC Press LLC 9588ch 06 frame Page 81 Wednesday, September 5, 2001 9: 46 PM of collisions of these marble-like molecules in a given time Quantum theory of the 1920s introduced the idea of probability, and the round-sphere idea was replaced by the probability function Building on the Arrhenius activation energy idea and... be prepared to hold the tube in a pure -air or nitrogen stream of known flow rate and at a constant temperature A tube holder may be made from a standard vacuum trap with the tube in the center well and the outer section filled with glass beads to promote heat exchange The tube holder is © 2002 by CRC Press LLC 9588ch 06 frame Page 84 Wednesday, September 5, 2001 9: 46 PM placed in a constant temperature... of being changed to provide several measuring ranges © 2002 by CRC Press LLC 9588ch 06 frame Page 79 Wednesday, September 5, 2001 9: 46 PM Two infrared sources are used, one for the sample energy beam, the other for the reference energy beam The beams are blocked simultaneously ten times per second by the chopper, a two-segmented blade rotating at five revolutions per second In the unblocked condition,... ambient conditions, the use of a chromatographic column is not warranted since the sulfur in ambient air is usually in the form of SO2 6. 8.5 HYDROCARBONS BY FLAME IONIZATION A simple hydrocarbon monitor can be built using a flame ionization detector Carbon atoms produce ions in a hydrogen flame Thus, the air stream containing hydrocarbons is fed into a hydrogen flame The ions produced are detected by an . system of Figure 6. 1. FIGURE 6. 1 Conception of a surveillance and control system. 9588ch 06 frame Page 72 Wednesday, September 5, 2001 9: 46 PM © 2002 by CRC Press LLC 6. 6 TYPICAL AIR SAMPLING. for which concentrations are desired, i.e., 15-min, 1-h, 3-h, 8-h, 12-h, or 24-h time intervals. It should be consistent with the averaging times specified by air quality standards. For example, in assessing. www.epa.gov/ttnami1/siteindx.html. Figure 6. 3 is a schematic flow diagram of a general continuous air- quality mon- itor. The device contains: 1. Primary air- moving device, usually a vacuum pump, to pull the air sample through