Study on Short-lived Climate Pollutants in Hanoi in the Context of Climate Change and Sustainable Development

Overview: BC and PM 2.5 variations were similar with each other, while features of TO 3 variation did not always agree with them. Their concentrations varied with season o[r]

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY

DO DUY TUNG

STUDY ON SHORT-LIVED

CLIMATE POLLUTANTS IN HANOI IN THE CONTEXT OF CLIMATE

CHANGE AND SUSTAINABLE DEVELOPMENT

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY

DO DUY TUNG

STUDY ON SHORT-LIVED

CLIMATE POLLUTANTS IN HANOI IN THE CONTEXT OF CLIMATE

CHANGE AND SUSTAINABLE DEVELOPMENT

MAJOR: CLIMATE CHANGE AND DEVELOPMENT CODE: 8900201.02QTD

RESEARCH SUPERVISOR: Prof Dr KAZUYUKI KITA

i PLEDGE

In writing Master’s thesis, I carefully read the thesis guidelines at Vietnam Japan University, Vietnam National University and fully understand what is written there and comply with all related rules and guidelines I ensure that this thesis is my own research and has not been published The use of results of other research and documents must comply with the regulations Citations and references for documents, books, research papers and web pages must be on the list of references of the thesis

I pledge my honor that I comply with provisions give above

Author of the thesis

ii TABLE OF CONTENTS

PLEDGE i

LIST OF TABLES iv

LIST OF FIGURES v

LIST OF ABBREVIATIONS vii

ACKNOWLEDGEMENT viii

ABSTRACT ix

CHAPTER BACKGROUND AND OBJECTIVES 1

1.1 Definition of SLCPs and their significance

1.2 Definition of BC, TO3 and PM2.5 and their significance

1.2.1 BC 8

1.2.2 TO3 10

1.2.3 PM2.5 12

1.3 Preceding Studies: Status of SLCPs in Vietnam and Southeast Asia 13

1.4 Mitigation measures to reduce SLCPs in Vietnam and SE Asia 21

1.5 SLCPs’ sources in Vietnam 22

1.6 Objectives of this study 24

CHAPTER METHODOLOGY AND STRATEGY IN THIS STUDY 25

2.1 Strategy to attain the objectives 26

2.2 Ground-based Observation 28

2.2.1 BC 29

2.2.2 Tropospheric Ozone 31

2.2.3 PM2.5 34

2.3 Signatures indicating contributions of local/regional/remote sources 36

2.3.1 Diurnal variation 36

2.3.2 Correlation of observed SLCP concentration levels with the trajectory and local meteorological parameters 37

2.4 Remote Observational Sites 41

2.4.1 Initial Data Processing 41

2.4.2 Observational Data Provided by Other Activities 41

2.5 Meteorological Data and Trajectory Analysis 42

2.5.1 HYSPLIT Trajectory Model 42

2.5.2 Local Meteorological Data 42

CHAPTER RESULTS 43

3.1 Observed SLCPs’ Concentrations and Their Variation 43

3.1.1 Winter 45

3.1.2 Spring 47

iii

3.1.4 Autumn 49

3.2 Seasonal Features of Trajectories 53

CHAPTER ANALYSIS AND DISCUSSION 55

4.1 Correlation between SLCPs in each season 55

4.1.1 BC and PM2.5 55

4.1.2 PM2.5 and TO3 57

4.2 Comparison of Observed Enhances of SLCP with the Transport Areas in each season 59

4.2.1 Winter 60

4.2.2 Spring 62

4.2.3 Summer 62

4.2.4 Autumn 63

4.3 Comparison of Observed Enhances of SLCP with the local / regional transport features 64

4.4 Comparison of Multi-station Observational Data 65

4.5 Discussion on contribution of local/regional sources in Northern Vietnam and on the inference of SLCP Climate Effect in this region 67

4.5.1 Contribution of local/regional sources in Northern Vietnam 67

4.5.2 Climate Effects of BC 67

CHAPTER CONCLUSION 66

REFERENCES 67

iv LIST OF TABLES

v LIST OF FIGURES

Figure 1.1. Critical air polluted condition in Hanoi by open biomass burning Figure 1.2. Global annual mean distribution of BC direct radiative forcing at TOA Figure 1.3 Radiative Forcing Caused by Human Activities Since 1750 Figure 1.4. Model of CO2 and SLCP cuts compared with other pathways until 2100 .4 Figure 1.5. Dominant sources of BC from human activities Figure 1.6. Schematic Display of Photochemical Ozone Formation in the

Troposphere 10 Figure 1.7. Diagram shows PM2.5 particles size 12 Figure 1.8. Planetary boundary layer (PBL) heating by surface emission of BC 15 Figure 1.9. Monthly mean BC mass concentration (left) and heating rate (right) over Ahmedabad in 2008 16 Figure 1.10. Vertical profiles of heating rate due to aerosol black carbon calculated from FBC profiles 17 Figure 1.11. Annual mean model median change in near-surface temperature (top left), zonally averaged temperature change for the model median (black line) and individual models (top right) .18 Figure 2.1. Initial strategy of research activities in this study 26 Figure 2.2 Updated strategy to attain objectives of this study 28 Figure 2.3 Schematic diagram of Particle Soot Absorption Photometer (PSAP) 30 Figure 2.4 Flowrate calibration in PSAP 30 Figure 2.5 Schematic diagram of dual-beam UV-absorption ozone photometer 32 Figure 2.6 Schematic diagrams of the newly developed PM2.5 sensor: 34 Figure 2.7 PM2.5 optical sensor calibration 35 Figure 2.8. Three typical patterns of BC, O3 and PM2.5 concentration in Hanoi 36 Figure 2.9. Local, regional and remote sources to Hanoi 39 Figure 2.10. Screenshot of monitoring portal of CEM website

http://enviinfo.cem.gov.vn/ 41 Figure 2.11. Screenshot of monitoring portal of AQICN website http://aqicn.org/ 42 Figure 3.1. Monthly average of BC, PM2.5 and TO3 in Hanoi in 2019 44 Figure 3.2. Timeseries of BC, TO3 and PM2.5 in Hanoi associated with

meteorological data in winter 2019 47 Figure 3.3. Timeseries of BC, TO3 and PM2.5 in Hanoi associated with

meteorological data in spring 2019 48 Figure 3.4. Timeseries of BC, TO3 and PM2.5 in Hanoi associated with

vi Figure 3.5. Timeseries of BC, TO3 and PM2.5 in Hanoi associated with

meteorological data in autumn 2019 49

Figure 3.6. Hourly concentration of PM2.5, BC and O3 in Hanoi 51

Figure 3.7. PM2.5 concentration in Hanoi during Tet 2020 compared with 2019 52

Figure 3.8. SLCPs in Hanoi during lockdown as coronavirus widespread 53

Figure 3.9. PM2.5 of Hanoi in April 2020 compared with April 2019 53

Figure 3.10. Trajectories of SLCPs in Hanoi associated with meteorological data in wintertime 2019 54

Figure 3.11. Time series of BC, TO3 and PM2.5 in Hanoi associated with meteorological data in 2019 55

Figure 4.1. Correlation of BC and PM2.5 in each season 56

Figure 4.2. Correlation of TO3 and PM2.5 in each season 57

Figure 4.3. Photochemical smog in Hanoi 58

Figure 4.4. SLCP Transport Areas in each season 60

Figure 4.5 Winter variation of SLCP Transport Areas 61

Figure 4.6 Spring variation of SLCP Transport Areas 62

Figure 4.7 Summer variation of SLCP Transport Areas 63

Figure 4.8 Autumn variation of SLCP Transport Areas 64

Figure 4.9 Comparison of transport features and observed enhances of BC and PM2.5 65

Figure 4.10 Diurnal variation of BC and TO3 in Hanoi 65

Figure 4.11 PM2.5 in Hanoi compared with coastal cities in Northern Vietnam 66

Figure 4.12. Atmospheric heating rate of BC 68

(Source: Ramachandran and Kedia, 2009) 68

Figure 4.13. BC concentration in Tokyo have decreased time by stringent regulations for PM emissions 69

vii LIST OF ABBREVIATIONS

BC Black Carbon

DRF Direct Radiative Forcing HFCs Hydrofluorocarbons

NMHC Non-methane Hydrocarbon

NMVOC Non-methane Volatile Organic Compounds PM2.5 Particulate Matter 2.5

RS Remote Sensing

SLCPs Short-lived Climate Pollutants TO3 Tropospheric Ozone

TOA Top of the Atmosphere UFP Ultra-Fine Particle

viii ACKNOWLEDGEMENT

I would like to express my gratitude to Professor Kazuyuki Kita for his tireless guidance and training It’s barely impossible to conduct this research without his lead

I thank VJU staff and lecturers, Dr Akihiko Kotera, Dr Hoang Thi Thu Duyen, Ms Bui Thi Hoa for their great help in doing this project, especially in the hard time of coronavirus pandemic, so that this study can continue to moving forward

ix ABSTRACT

Simultaneous observation of black carbon (BC), tropospheric ozone (TO3) and particulate matter 2.5 (PM2.5), which are significant climate forcers, was carried out at Hanoi to clarify the concentrations and variations of Short-lived Climate Pollutants (SLCP) in Hanoi and Northern Vietnam The research applied HYSPLIT trajectory model to distinguish contribution source regions of SLCPs to Hanoi Since we cannot use remote sensing for aerosol optical depth (AOD) analysis during wintertime, especially January, due to thick cloud coverage over Hanoi, we deployed remote PM2.5 stations surrounding Hanoi and coastal region in Northeast sector of Northern Vietnam to compare upwind/downwind concentrations

The results showed monthly average of BC, daytime TO3 and PM2.5 as 1-3μg/m3, 21-55ppbv, 18-65μg/m3, accordingly Both BC and PM2.5 were remarkably increased during rush hours or night-time in diurnal variation In contrast, TO3 was often high at noon and depleted to zero at night These diurnal variations can be attributed to their local/regional emissions and production of them near Hanoi The climax episodes of BC and PM2.5 were observed in wintertime, especially in January with periods lasting from day to week These high rises were mostly associated with winter monsoon trajectories from South China Sea, which actually transported emissions from North East region of Northern Vietnam These results firstly show a large contribution of Northern Vietnam sources of SLCP to their concentrations

1 CHAPTER BACKGROUND AND OBJECTIVES

“Science is where revolutions happen.”

~Carlo Rovelli As a physicist and bestselling author, Carlo Rovelli, a professor at Aix-Marseille University has guided thousands of readers through a marvelous adventure of physical world in his wonderful book named ―Seven Brief Lessons on Physics‖ In this book, he also wrote: “Ever since we discovered that Earth is round and turns

like a mad spinning-top, we have understood that reality is not as it appears to us”.

Overall, the Earth and the Universe still conceal many uncertainties and mysteries from us Our mission is to find them out This will not only help us to survive from current threats and moving on but also enable us to tackle the incoming challenges in the future

In this chapter, we will review the decadal efforts of scientists and researchers to improve our understandings on black carbon, tropospheric ozone, and their impacts on our climate system by comparing observations and simulations

However, before coming to basic definitions of SLCPs’ species and updated mechanisms of their climate impact, we can have a look through a story behind a picture, which was taken nearby my place in Hanoi, evidently showed the

threatening existence of black carbon in everyday life of local residents

2 In this above picture, local people were still doing exercises in a really bad condition of air quality of black and thick smoke from biomass burning nearby the stadium After two rounds, a middle-aged runner started coughing and walking slowly to the source of the smoke There he met the burner burning leaves and trash behind his house The conversation between them shifted from a low tone request to a furious quarrel The thing that stopped them from diving into each other with kicks and punches was just a fence Suddenly, the fire became so much bigger and caught into the house of the burner Someone started screaming The burner stopped his ―loud conversation‖ with the middle-aged man and urged people around to help him extinguish the fire

It’s clear that no one could force the burner to stop burning leaves in the backyard behind his house, but his own threat Every action has a motive

Whenever I crossed by the burnt house outside the stadium, I thought that if those two men observed the small flame calmly and consciously, they would have soon realized that it could turn into a really big fire in that dry and windy day Then, the tragedy could have been avoided

1.1 Definition of SLCPs and their significance

Several air pollutants, which have significant warming effects and short lifetime in atmosphere, are called Short-lived Climate Pollutants (SLCPs) Significant SLCPs are black carbon (BC) and tropospheric ozone (TO3) Besides, SLCPs also include non-pollutants such as methane and hydrofluorocarbons (HFCs), which are also referred as Short-lived Climate Forcers (SLCFs)

3 and sustainable development has not received enough concern from Vietnam

academia and policy makers

Figure 1.2. Global annual mean distribution of BC direct radiative forcing at TOA (Source: Wang et al., 2014)

Figure 1.3 Radiative Forcing Caused by Human Activities Since 1750 (Source: EPA, 2016)

TO3 BC

Other

4 Recent studies have shown that radiative forcing by SLCP increase is evaluated to be comparable with that by CO2 Sum of radiative forcing by SLCPs is estimated to be 1.75W/m2, larger than 1.66W/m2 of CO2

Although the lifespan of SLCPs in the atmosphere is much shorter than carbon dioxide (SLCPs’ is hours to years, while CO2 is a decade to century), SLCPs’ radiative forcing is significant compared with CO2 According to a research of EPA in 2016, the positive warming effect of BC, TO3 and methane in total is comparable with that of CO2 and accounts for around half of total radiative forcing caused by human activities

Because of long lifetime of CO2, only mitigation actions on CO2 are insufficient, but cutting down SLCPs is necessary to achieve 1.5 C target by 2030 according to

SR 1.5 ̊C IPCC 2018

5 The short atmospheric lifetime of SLCPs means that their concentrations can be reduced in a matter of weeks to years after emissions are cut, with a noticeable effect on global temperature within the following decades In contrast, CO2 has a long lifetime, so the majority of the climate benefits will take many decades to accrue after the reductions Long-term warming, however, will be essentially determined by total cumulative CO2 emissions – assuming SLCPs are eventually reduced – and will be effectively irreversible on human timescales without carbon removal Thus SLCPs and CO2 both have important effects on climate, but these occur on very different timescales (CCAC, 2014)

According to Special Report 1.5°C of IPCC, Human-induced warming has reached approximately 1°C above pre-industrial levels since 2017 At the present rate, the global temperature would reach 1.5°C around 2040 Pledges contained within current NDCs are insufficient to put the world on a course to 1.5 ̊C, even with the maximum rates of change post-2030 available in the models (IPCC, 2018)

It should be taken into consideration that global temperatures could pass 1.5 C sooner if emissions not decrease For example, the 1.5 ̊C guardrail could be crossed as early as 2030 if emissions follow the high emissions RCP8.5 scenario from IPCC’s 5th Assessment Report Following that scenario, even for a short period, would make achieving a 1.5 ̊C virtually impossible (IPCC, 2013)

6 Table 1.1. Key features of SLCPs compared with CO2

RF

Agents (W/mRF 2)

Lifetime in the

atmosphere Main Sources

Environmental Effects

BC +0.60(best

estimated) 4-12 days

Fossil fuel combustion (40%), biomass burning (40%), biofuels

(20%)

Health: carrier of toxic chemicals to the human body as

PM2.5

TO3 +0.35 Hours - Weeks

Precursor pollutants (CO, CH4, NMVOC, NOx)

after photochemical reaction Health: Cardiovascular, Respiratory diseases Agriculture: reduction of crop yield by damaging

ability to absorb CO2

CH4 +0.48 12 years

Agriculture as a key factor contributing

40% globally Increase of TO3

HFCs +0.32 Up to 29 years conditioning, foam Refrigerator, air-agents, solvents

Reduction of stratospheric O3

CO2 +1.66 200 years industrial processesFossil fuel and Ocean acidification

7 and clean air benefits (UNEP & WMO 2011; UNEP 2011a, UNEP 2011b) Fast uptake of these cost-effective and readily available measures, which target emissions of short-lived climate pollutants (SLCPs) in key sectors, could bring rapid and multiple benefits for human well-being These measures are spread across a variety of sectors, from waste management, where CH4 emissions can be harnessed as a source of energy, to transport, where high-emitting vehicles can be eliminated to reduce BC emissions, to industry where new technologies can be phased in to avoid use of HFCs with a high global warming potential (GWP) “If someone proposed that you could save close to 2.5 million lives annually, cut global crop losses by around 30 million tonnes a year and curb climate change by around half a degree Celsius, what would you do? Act, of course‖ UNEP’s Executive Director, Achim Steiner, has written “More than a decade of painstaking science has built a case that cannot be ignored, namely, that swift action on the multiple sources of black carbon, HFCs, and methane can deliver extraordinary benefits in terms of public health, food security and near term climate protection‖ (CCAC, 2014)

Based on scientific evidence, Climate and Clean Air Coalition in 2014 stated that the rapid and large-scale implementation of SLCP control measures could deliver near term multiple benefits for climate change and sustainable development Recent reports have identified 16 BC and methane measures that can deliver significant benefits to human well-being by protecting the environment and public health, promoting food and energy security, and addressing near term climate change These measures involve technologies and practices that already exist and in most cases are cost effective (CCAC, 2014)

8 In short, SLCPs are responsible for a substantial fraction of near-term climate change, with a particularly large impact in sensitive regions of the world, and can have significant, detrimental health, agricultural and environmental impacts However, the challenge is yet to be fully recognized by the international community (CCAC, 2014)

1.2 Definition of BC, TO3 and PM2.5 and their significance 1.2.1 BC

Black carbon (BC) is a tiny black particle that contributes as a major component of particulate matter 2.5 (PM2.5) In atmospheric science and climate change study, BC is defined as a potent climate-forcing aerosol that is mostly removed from the atmosphere by wet deposition and remains in the atmosphere for only a few days or weeks (U.S EPA, 2012) Since BC is able to absorb incoming solar radiation and cause atmospheric heating in local or regional area, BC is also called as a light absorbing aerosol and takes part in Earth’s climate system with a unique and important role (Bond et al., 2013)

As BC is a product of the incomplete combustion of fossil fuels, biofuels, and biomass, the main sources of black carbon are open burning of biomass, diesel engines, and the residential burning of solid fuels such as coal, wood, dung, and agricultural residues (U.S EPA, 2012) When suspended in the atmosphere or deposited on ice or snow, BC contributes to global warming by heating surrounding

9 Figure 1.5. Dominant sources of BC from human activities

(Source: CCAC, nd.)

In terms of climate effect, BC heats surrounding atmosphere by absorbing incoming solar radiation, leading to regional and global warming BC also contributes to warming in polar region and to melting Antarctic ice by depositing on cryosphere BC is always emitted with co-pollutants, such as organic carbons and sulphates, which can have neutral or even cooling effect by dimming the sunlight and increase the reflection ability of local or regional atmosphere Therefore, BC and co-pollutant particles may disturb the rainfall patterns by modifying atmospheric circulation (semi-direct effect) and may affect Indian monsoon These effects would create impact on agriculture production, food security and sustainable development of vulnerable countries, especially the ones in Asia and Africa

10 1.2.2 TO3

Ozone is a highly reactive gas composed of three oxygen atoms It is produced naturally in the stratosphere and is majorly produced from air pollutants in the troposphere Depending on where it is in the atmosphere, ozone affects life on Earth

in either good or bad ways (EPA, 2012)

Figure 1.6. Schematic Display of Photochemical Ozone Formation in the Troposphere

(Source: CCAC, 2014)

11 fuel power plants, oil refineries, the agriculture sector and a number of other industries (UNEP, 2011)

Although the lifetime of TO3 is just a few hours in the atmosphere, its impact to our climate system and social system is significant TO3, of which CO, NMHC, NOx are the main precursors, is also a major air pollutant, which damages ecosystem structure and functions and the health and productivity of crops, thus threatening food security O3 also reduces the ability of plants to absorb CO2, altering their growth and variety

TO3 has strong greenhouse effect because it absorbs infrared radiation from the earth surface in the atmospheric window at around wavelength of 9.6μm

To the matter of human health, TO3 makes it more difficult to breathe deeply and vigorously, shortness of breath and pain when taking deep breaths, or coughing and sore throats It can cause respiratory diseases such as asthma, emphysema, lung cancer, chronic bronchitis, etc., TO3 is dangerous to children, old people, and sensitive patients (EPA, 2019)

12 1.2.3 PM2.5

PM2.5 are tiny particles whose diameter is smaller than 2.5 micrometer (30 times smaller than human hair), and their major components are sulfate aerosol,

secondary organic aerosol and BC

Figure 1.7. Diagram shows PM2.5 particles size (EPA, nd.)

13 waste and wildfires It is also produced from vegetation, construction sites, metal and chemical industry, etc

PM2.5 except for BC has cooling effect by scattering solar radiation (parasol effect) Some PM2.5 components such as sulfate aerosol are significant as condensation nuclei to producing clouds and rain

Because PM2.5 particles are small enough to be breathed into deep lung and they can cause premature deaths According to WHO, the global deaths every year on PM2.5 is about million people and it is increasing fast in developing countries, especially Southeast Asia Recently, the number of researches on PM2.5 has been increasingly conducted in many countries due to its critical impacts on human health

In this study, PM2.5 is used as a proxy of BC, because their concentrations generally show a tight positive correlation and because PM2.5 concentration can be continuously measured much easier than BC concentration

1.3 Preceding Studies: Status of SLCPs in Vietnam and Southeast Asia SLCPs observation in Vietnam

Several studies have shown concentrations of BC and TO3 based on in situ observations in Vietnam However, they were mostly focused on air pollution No simultaneous observation of BC and TO3 have been conducted so far

14 Concerning the air pollution and photochemical smog in Hanoi, D.D An et al (2008) stated that photochemical smog potential in Hanoi at that time was still low Analyzing hourly ozone concentrations in year data (2002-2003), the result of this study indicated that the high episode of TO3 was in March with ozone concentration larger than 46ppb and the emission sources were VOC and NOx emissions from industrialization and transportation in the city

Sakamoto et al (2017) observed TO3 and its precursor pollutants CO, VOC and NOx in Hanoi, inner city area from 2015-2016 (1-year observation) The results from this research stated that the daily mean value of TO3 was 19.3 ± 15.3 ppb and the correlation among CO, VOC and NOx indicated that the emission mainly originated from vehicles including motorcycles, as well as buses, trucks and cars were the main sources of ozone precursors throughout the year

Investigating the seasonal and sub seasonal variation of ozone mixing ratio (OMR) in Hanoi, Ogino et al (2013) mentioned that the minimum OMR shown in winter and maximum OMR found in spring and summer By analyzing 7-year ozonesonde data from Hanoi, the authors of this study concluded that low OMR air masses were transported from the equatorial troposphere in winter, and high OMR air masses are transported from the midlatitude stratosphere in summer

15 Climate influence of SLCPs in SE Asia

Figure 1.8. Planetary boundary layer (PBL) heating by surface emission of BC BC particles absorb solar radiation and heat surrounding air, known as their direct effect Ramachandran and Kedia (2010) calculated the atmospheric heating rates based on the observed BC concentration and showed that heating rates including BC aerosols are at least a factor of higher than when BC aerosols are absent However, the heating effect of BC is not very significant at the ground surface, because the atmospheric heating by BC is smaller than that by absorption of solar radiation by the ground In contrast, Tripathi et al (2007) and Wang et al (2018) calculated altitude profiles of the heating rate by BC was high throughout the surface boundary layer although BC concentration gradually decreased with altitudes Wang et al (2018) indicated that BC increased atmospheric temperature at altitudes around the top of the surface boundary layer and that BC did not change the surface temperature directly

16 circulation and distribution of precipitation, so-called semi-direct effect (e.g Koch and Del Genio, 2010) Lee and Kim (2010) suggested that BC radiative forcing could change the circulation pattern to reduce precipitation especially in Southeast Asia

Although the climate influence by BC is difficult to quantitatively understand because it depends on various parameters: particle size, mixing state, altitude distribution, atmospheric adjustment and so on (Matsui et al., 2018; Takemura and Suzuki, 2019), many model studies predicted that increase of BC emission cause significant temperature increase near surface (Stjern et al., 2017; Sand et al., 2020)

Figure 1.9. Monthly mean BC mass concentration (left) and heating rate (right) over Ahmedabad in 2008

17 Figure 1.10. Vertical profiles of heating rate due to aerosol black carbon calculated

from FBC profiles

18 Figure 1.11. Annual mean model median change in near-surface temperature (top

left), zonally averaged temperature change for the model median (black line) and individual models (top right)

(Source: Stjern et al., 2017)

19 Although few studies have been focused on climate change by SLCPs in Southeast Asia so far, it was studied as a part of Asian climate change especially in China and India The understanding about BC aerosols, ozone and their effects on regional and global climate has been improved through time

Meehl et al (2008) mentioned possible effects of BC aerosols on Indian Monsoon By simulating six-member ensemble of twentieth century with only BC varying whereas, natural and human-induced forcing fixed with their pre-industrial values, the researchers experimented the effects of BC over South and Southeast Asia Differences of BC simulations showed that the radiative effects of BC aerosols were most dramatic during the dry season over South Asia, and changes in the temperature of air masses over India and Tibetan Plateau due to absorption and reflection solar radiation of BC aerosols would lead to anomalous inflow from Indian Ocean to the south and increased precipitation over most of India in the pre-monsoon period (March, April, May) In summer, BC also weakened China rainfall while enhanced precipitation in Southeast Asia and Japan This study pointed the significance of BC aerosols for rainfall pattern over most of Asia and Indian Monsoon in particular

20 BC RF from -101%/+152% to -70%/+71% over Asia and constrained BC RF of 0.61 W/m2 This is the best estimate until now This implied that reduction in BC emissions would contribute to decrease the rate of global warming, but the contribution could be less than previous thought

In general, researchers in nearly a decade have found evidence linked SLCPs to climate change, especially regional climate in Southeast Asia Chen et al (2017) also confirmed direct radiative forcing of anthropogenic aerosols, TO3 and greenhouse gases and indicated that aerosol influence may change wind flow and precipitation in East, Southeast, South Asia in winter This one more time rang the bell for policy makers, entrepreneurs and stakeholders to take SLCP’s cut into serious consideration

Hang (2014) evaluated the impact of BC aerosols to temperature and precipitation of Vietnam and surrounding regions from 1991 to 2000 by using RegCM 4.2 and module Chem_aerosol through experimental simulation: no aerosols; BC from human and biomass burning; and dust The results showed the average BC as 0.92 – 1.17 mg/m2 The high rises of BC lasted from Nov to Mar, while low BC was from Jun to Sep due to wet deposition in rainfall season BC caused temperature decrease in almost region, significant decrease in winter in India, Southeast China, Myanmar, Lao, N Vietnam from -0.3 to -0.8 Celsius degree Less decrease of T in summer and autumn (-0.1 to -0.3) in Lao and N Vietnam BC impact and dust impact on precipitation was not clear however dust impact on rainfall was in larger than that of BC In July, dust caused -8mm/month decreased precipitation in Myanmar and N Vietnam

21 2006 data file The simulation of emissions (PM10, PM2.5, SO2, dust) showed applicability and could be applied in many other projects

Beside reducing warming effect, SLCP’s cut could also reduce the rate of sea-level rise ~20% in the first half of the century according to recent studies By 2100, the combined mitigation of CO2 and SLCPs could reduce the rate of sea-level rise by up to 50%, and cumulative sea-level rise by about 30% as compared to the same scenario (Hu A et al 2013)

1.4 Mitigation measures to reduce SLCPs in Vietnam and SE Asia

A number of countries participated in the Climate and Clean Air Coalition (CCAC), a voluntary partnership of governments, intergovernmental organizations, businesses, scientific institutions and civil society organizations, for improving air quality and protecting the climate through actions to reduce short-lived climate pollutants (CCAC, nd)

Vietnam has become a partner of CCAC since 2017 to cooperate in implementing measures to mitigate methane in agriculture sector, especially in rice cultivation In Vietnam, agriculture sector is responsible for 33% of total greenhouse gas emissions with livestock and rice production as primary sources Therefore, it is understandable and efficient to start cutting down methane as the first commitment of reducing short-lived climate pollutants This is not only an ensured feasible approach but also a foreseeable efficient plan as Vietnam’s economy is transforming from agriculture sector to industry and service sector In addition, Vietnam starts contribution to cut down other SLCPs; requesting funding from

CCAC to conduct a national HFC inventory

22 In Southeast Asia, other countries have been actively contributed to SLCPs’ reduction Thailand is developing their understandings on emissions of BC and precursor pollutants of TO3 from biomass burning, vehicles and industrial production Lao is focusing on HFCs, municipal solid waste and agriculture

1.5 SLCPs’ sources in Vietnam

Kurokawa and Ohara (2019) estimated air pollutants emissions including BC emission in Asia to make the Regional Emission inventory in ASia (REAS) version 3.1, and showed NOx, most significant ozone precursor, and BC emission from Vietnam was 568 and 64 Gt/year in 2015 These values are larger than those from Laos, Myanmar and Cambodia, similar to those from Thailand and Philippines, and much less than those from China and India

Local sources

- Vietnam has become one of the top air-polluted countries in over the world (Thermal energy generation, construction and transportation)

- Local sources: biomass open burning, thermal power generation, industry, transportation

Remote sources

Vietnam is located in the tropics near Pacific Ocean Therefore, it is highly impacted by monsoonal winds Winter monsoon associated with the Siberian High transports air mass from China to Northern Vietnam Summer monsoon associated with Indian Ocean High air mass from India, Thailand, Myanmar and Lao to the Northern Vietnam

24 1.6 Objectives of this study

- To make clear the concentrations of BC, TO3 and PM2.5 in Hanoi and the features of their variations based on in situ observations

25 CHAPTER METHODOLOGY AND STRATEGY IN THIS STUDY

“In the real life, I was told, one had to abandon the impossible and embrace the practical.”

“Give the impossible a chance.”

~Michio Kaku Without a solid background in advanced physics, the young Michio Kaku realized that he would be forever speculating about futuristic technologies without understanding whether or not they were possible “I realized, I need to immerse

myself in advanced mathematics and learn theoretical physics,” Michio said “So

that is what I did”

Constructing particle accelerator to create antimatter in a high school science fair was the first ambitious project of young Michio, which earned him a ride to Harvard Today, Michio is known as the co-founder of string theory, finishing what Einstein started, combining the theory of general relativity and quantum mechanics More evidence and better understanding on string theory may one day allow us to travel between universes, into new dimensions, or even time travel

That is what people talked about Michio, actually I was more impressed with what he described about Michael Faraday, the ―father‖ of force fields, which were previously thought to be useless Today, the light that we are using, and all the electricity, computers and internet are driven by force fields of Faraday He has created forces to build our modern civilization However, not so many people know that the poor young Faraday was illiterate in mathematics Consequently, his notebooks are full of hand-drawn diagrams, not of equations “Ironically, his lack

26 Inspired by Michio and Faraday, I struggled to embrace this research without a solid background in natural science

2.1 Strategy to attain the objectives

In order to achieve two objectives of this study, I apply the combination of the observation of SLCPs, their source information, and the meteorological analysis I have observed data of black carbon, tropospheric ozone and particulate matter 2.5 in Hanoi since December 2018, while I was in second semester of Master Program of Climate Change and Sustainable Development in Vietnam - Japan University Although these atmospheric compounds have been observed separately in Vietnam, it is probably the first time to observe them simultaneously and compared This simultaneous observation will enable us to discuss their correlation to examine local source contribution This is a significant advantage of this study

27 Figure 2.1.1 illustrates the original strategy of this study to attain our objectives To answer the questions (i) what is the concentration of SLCPs in Hanoi and how they vary, we started and based on observational data as the primary data, because reliable observations can directly provide these information To get the answer for the question (ii) where they come from and what source contribute to increase SLCPs in Hanoi, we planned the correlation analyses of source distribution data and meteorological data with the observational data After the data processing of black carbon, tropospheric ozone and particulate matter 2.5 to see the correlation, we firstly examine their correlation and their diurnal variations Secondly, comparing the observed variation of SLCP concentrations with the transport routes estimated by the trajectory analysis, contributions of local/regional emission and that of the transport from remote sources can be examined

In this study, a large contribution of remote sources was projected Contributions of various remote source would be estimated from the integration of emission amount based on the inventory data along air mass trajectories Because biomass burning emission has large variability, its contribution would be estimated using open burning signature derived from the remote sensing data along the air mass trajectory Comparing correlations of the observed variation with these estimation of various sources, we can estimate that relative significance of them

28 Figure 2.2 Updated strategy to attain objectives of this study

2.2 Ground-based Observation

The primary data of this research are collected from our ground-based observation system which is provided by Professor Kazuyuki Kita with the support from JICA, Ibaraki University and Vietnam Japan University The instruments to measure BC and PM2.5 have been calibrated before shipping, the instrument to monitor TO3 requires no calibration The detailed description, data processing and calibration will be described specifically each by each in below sections The incoming air flow to BC and TO3 was pumped to one inlet, then it was separated to each BC and TO3 instrument with different specialized tubes to ensure the same air sample and accuracy for measurement All three instruments have been observed in VJU - MCCD office since December 2018

29 2.2.1 BC

• Instrument:

The Particle Soot Absorption Photometer (PSAP) is used to measure in near real time the optical extinction coefficient for absorption which can be used to estimate the corresponding concentration of fine particle soot The method is based on the generally accepted integrating plate technique (IP) in which the change in optical transmission of a filter caused by particle deposition is related to the optical absorption coefficient using Beer’s law and a calibration transfer coefficient The difference between the PSAP measurement and the standard IP method is that the PSAP measurement is continuous as particles are being deposited rather than a single, time integrated measurement Therefore, a continuous, time resolved measurement of absorption can be obtained Measurement time resolution can be as short as a few seconds to minutes depending on aerosol soot concentration The calibration transfer coefficient was determined from measurements on aerosol with known absorption and is filter type dependent (SR Springton, 2018)

The principle features of the PSAP are:

- The instrument is self-contained and requires only an external vacuum source to provide a sample flow of to lpm

30 Figure 2.3 Schematic diagram of Particle Soot Absorption Photometer (PSAP)

(Source: SR Springton, 2018)

• Data processing

Data from PSAP is processed by python programs under main steps - Step 1: Format raw data

- Step 2: Convert to CSV file

- Step 3: Level processing with 1-min average

- Step 4: Estimate BABS/BCMC data from decrease rate of filter light transmittance

- Step 5: Hourly average and making monthly data

• Flowrate calibration

31 BC data need conversion from BABS to MBC by applying the equation of Kondo et al 2009 considering light scattering by other aerosols Flow rate is corrected by comparison with precision flow meter in Step

MBC = Babs x SBC x Fp / (0.175 x 1.09 x Fp)

(Y Kondo et al, 2009) where

Babs (1/Mm) is absorption coefficient measured with PSAP instrument SBC (mass absorption cross section) = 1/15 (g/m

2 ) Fp : Flow rate (m3/s)

2.2.2 Tropospheric Ozone

- Instrument:

32

- Data processing:

Data from Ozone Photometer is processed by python programs under main steps - Step 1: Format raw data

- Step 2: Convert to CSV file

- Step 3: Level processing with 1-min average - Step 4: Hourly average and making monthly data - Flowrate calibration:

Dual-beam UV-absorption Ozone Photometer requires no calibration

34 2.2.3 PM2.5

- Instrument:

PM2.5 is measured by a palm-sized optical sensor produced by Sharp The PM2.5 mass concentration was calculated from distribution of light scattering intensity by considering the relationship between scattering intensity and particle size PM2.5

concentration values from this sensor have been calibrated (Nakayama et al., 2017) Figure 2.6 Schematic diagrams of the newly developed PM2.5 sensor:

(a) outside and (b) inside (Source: Nakayama et al., 2017)

35 will provide valuable information on the environmental and health effects of aerosol particles (Nakayama et al., 2017)

- Data processing:

Data from PM2.5 optical sensor is processed by python programs under main steps - Step 1: Format raw data

- Step 2: Level processing with 1-min average - Step 3: Hourly average and making monthly data - Sensor calibration:

Data from PM2.5 optical sensor using in this research has been calibrated by passing polystyrene latex (PSL) particles through a differential mobility analyzer (DMA) and an aerosol particle mass analyzer (APM) to remove signals corresponding with particles larger than 2.5μm (Nakayama et al., 2017)

Left figure is an example of temporal variations in light scattering signals detected by the PM2.5 sensor when measuring PSL particles with diameters of (a) 0.296 and (b) 0.498μm after passing these particles through the DMA and APM

36 2.3 Signatures indicating contributions of local/regional/remote sources

2.3.1 Diurnal variation

The diurnal variation signatures of SLCP concentrations could indicate the contribution of local emission and/or production of SLCPs First diurnal variation pattern is “Day-Night Variation‖ as Figure2.1.3(a) showing that ozone concentration is maximal in mid-daytime and nearly zero during nighttime, and that BC or PM2.5 concentrations are low during daytime but increase during night time This pattern is caused by on-site photochemical production of ozone and accumulation of aerosols due to little convection in nighttime The second typical diurnal variation pattern is “Increase during Rush Hours‖ which describes low ozone concentration but increasing BC and PM2.5 during morning and/or evening

rush hours as Figure2.1.3(b)

Figure 2.8. Three typical patterns of BC, O3 and PM2.5 concentration in Hanoi

B A B

37 These signatures indicate that BC, O3 and PM2.5 are significantly contributed by local sources In contrast, when a SLCP increase event caused by the influence of remote sources, simultaneous increase of all SLCP concentrations would be expected as Figure2.1.3(c)

2.3.2 Correlation of observed SLCP concentration levels with the trajectory and local meteorological parameters

Defining high, mid, low concentrations comparing with the mean plus/minus standard deviation range of each SLCP as shown below, we can classify the observed concentrations as shown in Figure 2.2

High (H) = larger than Mean value + St Dev

Medium (M) = within Mean +/- St Dev

Low (L) = lower than Mean - St Dev

After categorizing the observed concentration patterns in Hanoi, three typical patterns were found These diurnal variation patterns can be used as indicator of local pollution The most common pattern is ―Day-Night Variation‖ in which ozone is max in day time and nearly zero at night time, BC or PM2.5 concentrations are low in day time but increase at night time due to little convection This means that BC, O3 and PM2.5 are significantly contributed by local sources The second typical diurnal variation pattern is ―Increase during Rush Hours‖ which describes low ozone concentration but increasing BC and PM2.5 during rush hours

39 Table 2.1 Diurnal Analysis of BC, O3 and PM2.5 concentration in Hanoi

40 Table 2.2 Evidences for distinguishing local/remote source influences

Factor Local Regional Remote

Diurnal variation of SLCP concentration (Sc)

Clear diurnal variation (*) or Increase during

Rush Hours

Clear diurnal variation

No clear diurnal variation, but synoptic scale variation Dependence on local meteorological condition Clear dependence on local met Conditions (sunlight hours, wind direction/speed) Dependence on regional scale distribution of atmospheric pressure Trajectory Areas nearby Hanoi in different variations

of SLCPs

High BC/PM correlated with trajectories of longer

residence time inside Hanoi local

counted

No

Comparing upwind/downwind

PM2.5 station data

PMB < PMM PMC > PMM

PMHaiphong < PMHN PMHaiPhong ~ PMHN

TO3- Max in daytime, PM/BC – Max at night

41 2.4 Remote Observational Sites

- Two remote stations have been set up since January 2020 surround Hanoi, one in VNUF, Hoa Lac and the other located 5km from VJU

- Due to coronavirus pandemic and time limitation, data from these two stations have not been processed in this research yet.

2.4.1 Initial Data Processing

Data of PM2.5 from remote observational sites surrounding Hanoi were processed as hourly data to compare with data in VJU This helped confirm the sources of SLCPs transported to Hanoi If the concentration in remote sites and that in VJU are significant different then the source is quite localized Otherwise, the source is transported from regions nearby Hanoi or from surrounding countries

2.4.2 Observational Data Provided by Other Activities

- Data from Centre of Environment Monitoring Vietnam (CEM)

42

- Data from US Embassy to Hanoi

Figure 2.11. Screenshot of monitoring portal of AQICN website http://aqicn.org/

2.5 Meteorological Data and Trajectory Analysis 2.5.1 HYSPLIT Trajectory Model

Backward trajectories calculated from the meteorological data by using HYSPLIT model from NOAA to estimate the daily transport routes of SLCPs

Correlation of increase of SLCP concentrations with the trajectories indicates the contribution of remote source from each source region

Contribution of local sources would not show a correlation with the trajectories 2.5.2 Local Meteorological Data

43 CHAPTER RESULTS

“The first beginnings of things cannot be distinguished by the eye.”

~Lucretius1

3.1 Observed SLCPs’ Concentrations and Their Variation

Overview: BC and PM2.5 variations were similar with each other, while features of TO3 variation did not always agree with them Their concentrations varied with season obviously In wintertime, increase of BC, PM2.5 and TO3 episodically occurred In springtime, TO3 concentration showed its maxima around noon more regularly, while frequency and magnitude of episodic increase of BC and PM2.5 were lower than those in winter In summertime, amplitude and diurnal maximal values of TO3 concentration were largest, while average concentrations of BC and PM2.5 were smallest and showed small diurnal increases In autumntime, while amplitude and diurnal maximal values of TO3 concentration were also large, similarly to those in summer, diurnal maxima of BC and PM2.5 concentrations occurred in midnight more obviously In general, TO3 concentration showed maximal values around noon, while BC and PM2.5 concentrations often increased during nighttime In major high BC and PM episodes, ozone concentration was inverse proportional with them, indication of local source contribution Mid pollution episodes with correlation of ozone with BC/PM2/5 suggest that they are transported from remote sources Trajectory data are needed to confirm those differences

- Monthly averaged concentration of BC was in range of 5-10 μg/m3, and got maximum in January

44

- Monthly averaged concentration of PM2.5 was in range of 50-100 μg/m3, and got maximum in January

- Monthly averaged concentration of TO3 was in range of 20-30 ppbv, and got maximum in June

46 Most evident feature of BC, PM2.5 and TO3 variations in winter was episodic increase of their concentrations Period of this increases ranged from day to week This increase consisted of two components: diurnal variation and gradual increase and decrease Diurnal maxima of TO3 occurred just after noon, while those of BC and PM2.5 were found in nighttime PM2.5 concentration sometimes showed two maxima during one day; evening peak and morning peak Low concentration episodes also continued in periods of a few days In these periods, PM2.5 and TO3 concentrations were generally less than 30 μg/m3 and 25 ppbv, and diurnal variation was not clear These episodes mostly occurred with rainy weather Between increase and low episodes, intermediate concentrations were observed Diurnal maximal concentrations of PM2.5 and TO3 were around 50 μg/m3 and 21-55ppbv, and they were often found in nighttime for BC and PM2.5 , but in mid-daytime for TO3 It is probably significant that all BC, PM2.5 and TO3

47 Figure 3.2. Timeseries of BC, TO3 and PM2.5 in Hanoi associated with

meteorological data in winter 2019 3.1.2 Spring

Episodic increase of BC, PM2.5 were also observed in spring, but length and frequency were smaller than winter

TO3 increase was not generally seen in these periods

In other periods, TO3 concentration frequently showed its maxima larger than 50 ppbv at mid-daytime

In these periods, those of BC and PM2.5 were not clear They sometimes occurred in mid-day, sometimes occurred in the morning…

48 In these periods, low concentration episodes also continued in periods of a few days In these periods, PM2.5 and TO3 concentrations were generally less than 30 μg/m3 and 20 ppbv, and diurnal variation was not clear

Figure 3.3. Timeseries of BC, TO3 and PM2.5 in Hanoi associated with meteorological data in spring 2019

3.1.3 Summer

Summertime feature can be characterized by higher TO3 concentration in mid-daytime, often exceeded 100 ppbv It decreased to nearly zero from mid-night to sunrise

Concentration of BC and PM2.5 were generally low (show value) in summer

49 Figure 3.4. Timeseries of BC, TO3 and PM2.5 in Hanoi associated with

meteorological data in summer 2019

3.1.4 Autumn

Regular, high maxima of TO3 concentration in mid-daytime were also observed (>80 ppbv) It decreased to nearly zero from mid-night to sunrise

Concentration of BC and PM2.5 often also showed diurnal maxima (show values) in mid-night

Ozone maxima around 50 ppbv with no clear variation of PM were often observed These episodes were coincided with rainy weather

50 meteorological data in autumn 2019

51 Figure 3.6. Hourly concentration of PM2.5, BC and O3 in Hanoi

In January 2020, concentrations of BC, TO3 and PM2.5 still followed similar patterns with those of 2019, except for period of 24-26 January shown in Figure 3.1.2 The average of BC in this period displayed as 1.63 μg/m3, while the average BC concentration in January 2019 was 2.25 This indicated a decrease of nearly 30% of BC aerosols However, the missing data of BC from the second half of January 2020 forced us to examine its proxy PM2.5 concentration to confirm this decline

53 Figure 3.8. SLCPs in Hanoi during lockdown as coronavirus widespread

Figure 3.9. PM2.5 of Hanoi in April 2020 compared with April 2019

3.2 Seasonal Features of Trajectories

While the trajectories were relatively constrained in wintertime and summertime, they showed more dispersed in space during spring and autumn

54 This implied that there were only two possibilities of SLCPs source emissions in winter since air masses from sea or ocean normally clean compared with air masses form inland The first is emission from China, the second is from regional surrounding Hanoi in Northern Vietnam We will discuss further in Chapter In spring, the trajectories from inland China continued to degrade and transit to more directions from South and Southeast Asia

There was no typical source direction in springtime The wind could blow from any direction, except for North West of Hanoi

In summer, the trajectories became more constrained to South West of Vietnam (directions from India, Thailand or Lao) Although there was still a small number of trajectories from inland China in July, it is not typical characteristic of trajectory in summer

In autumn, the trajectories again became more dispersed and transited to more directions from South China Sea and inland China The number of trajectories from

Spring Su mm er Autu m n

Figure 3.10. Trajectories of SLCPs in Hanoi associated with

meteorological data in

55 North and North East of Vietnam quickly outweighed the one from South and South West The typical feature of summer trajectories disappeared in October and November

Figure 3.11. Time series of BC, TO3 and PM2.5 in Hanoi associated with meteorological data in 2019

CHAPTER ANALYSIS AND DISCUSSION

“If the ladder is not leaning against the right wall, every step we take just gets us to the wrong place faster.” — Stephen Covey 4.1 Correlation between SLCPs in each season

56 In this study, PM2.5 concentration is regarded as a proxy of BC concentration For the validation, we compared those concentrations in each season In all seasons, BC concentration showed positive correlation with that of PM2.5, although a considerable variability was found; BC concentrations were mostly between 1% and

10% in all seasons and the correlation with PM2.5 is from 54 to 65% Figure 4.1. Correlation of BC and PM2.5 in each season

57 This result performed that we can use PM2.5 concentration in qualitative discussion using relative values, although we need direct observation of BC values for the quantitative discussion

Variation of BC ratio to PM2.5 may be attributed to the difference of source type as well as progress of photochemical reactions producing secondary aerosols

Figure 4.2. Correlation of TO3 and PM2.5 in each season 4.1.2 PM2.5 and TO3

58 In some cases when concentrations of PM2.5 (and BC) showed their maxima in mid-daytime, TO3 concentration was very low

These results suggest negative correlation between TO3 and PM2.5/BC Figure 4.3. Photochemical smog in Hanoi

(Source: An et al 2008)

This general tendency of negative correlation as well as clear but different diurnal variation between TO3 and BC (and PM) strongly suggest that both SLCPs were produced in vicinity of the observation site (Hanoi)

59 BC and PM concentrations generally increased during nighttime and often had their maxima as NO in the above figure NO is mostly emitted as car exhaust or other high temperature combustion and it increases during night by accumulation under the stable air condition in night Similarly, BC and PM concentrations presumably increased during nighttime by accumulation of those emitted locally NO decreases after sunrise by two reasons: thermal convection excited by heating of ground surface by sunlight, and chemical conversion from NO to NO2 by reactions with ozone and other peroxides In the case of BC and PM, which are not lost by chemical reactions, their decrease could be attributed to the active convection, which can reduce their concentrations by mixing with upper, cleaner air In addition, alternation of sea breeze and land breeze can affect the diurnal variation In any way, these processes are significant in the case that local/regional sources are dominant

As noted in chapter 3, TO3 and BC (and PM) concentrations were often low during rainy weather Under rainy condition, photochemical production of TO3 was mostly stopped by lack of solar UV radiation and TO3 was reduced by conversion of NO to NO2 BC and PM could be reduced by wet removal by rain and clouds However, difference of wind transport in association with rainy weather system could also cause the decreases

4.2 Comparison of Observed Enhances of SLCP with the Transport Areas in each season

SLCPs in northern Vietnam region may be affected by their remote sources in surrounding countries as noted in Chapter

60 To distinguish remote areas where observed air masses would be affected, we counted the air mass residence time defined by the time that calculated trajectory points stayed in each area Considering that influence of sources in each area would increase with time that the observed air masses was located over the area, the residence time can be regarded as indicator of influence in each area It could be noted that we neglected that influence from a source area could reduce with distance the area because of diffusion/mixing which cannot be considered by the trajectory

In this study, we defined the following five areas: North Vietnam (1), China (2),

South China Sea (3), Southern SE Asia (4) and Western SE Asia (5) Figure 4.4. SLCP Transport Areas in each season 4.2.1 Winter

We compared the timing when high peaks of PM2.5 appeared with the residence time in the areas in wintertime of 2019

The peaks did not coincide with larger residence time in China

61 in China was reducing and that in SC sea increasing (red arrows) Blue arrows show the peaks also coincided with the peak of residence time in North Vietnam area

62 4.2.2 Spring

Figure 4.6 Spring variation of SLCP Transport Areas

Because there is no significant source in South China sea area, coincidence with large residence time in that area presumably shows simply a transport direction The transition between China and SC sea has two possibilities: coastal region of (south) China was significant source region or simply showing the transport direction

4.2.3 Summer

63 Some of the peaks occurred with peak or increase of residence time in Northern Vietnam area, implying slower wind speed

Other peaks occurred with peaks or long residence time in Sorthern SE Asia area

Figure 4.7 Summer variation of SLCP Transport Areas 4.2.4 Autumn

In autumn, PM concentration increased frequently with many spikes, which occurred at night or early morning

64 Other increase events occurred during long residence time in China area

Figure 4.8 Autumn variation of SLCP Transport Areas

4.3 Comparison of Observed Enhances of SLCP with the local / regional transport features

65 Figure 4.9 Comparison of transport features and observed enhances of BC and

PM2.5

In Figure 4.3.1, high BC and PM2.5 episodes were found associated to trajectories from southeast of Hanoi, not air masses from China Therefore, Southeast regional sources in North of Vietnam were significant

Diurnal variation of BC and TO3 strongly suggested active convection in the boundary layer to increase the temperature around top of the boundary layer

Figure 4.10 Diurnal variation of BC and TO3 in Hanoi 4.4 Comparison of Multi-station Observational Data

After sending request to Air Quality Network (AQICN.org) I got daily PM2.5 data from US Embassy to Hanoi and other stations of CEM in coastal cities in North of Vietnam

67 4.5 Discussion on contribution of local/regional sources in Northern Vietnam and on the inference of SLCP Climate Effect in this region

4.5.1 Contribution of local/regional sources in Northern Vietnam

In general, increase of SLCPs observed at Hanoi involved diurnal variation and anti-correlation between TO3 and BC/PM

This feature strongly suggests that major part of the photochemical production of TO3 and of the emission of BC/PM occurred at Hanoi and in Northern Vietnam region

Results of the trajectory analyses have indicated that transboundary transport from China could have secondary importance as source region

Relation of SLCP concentration and regional transport features…

Considering all these results, we can conclude most significant source region of BC and TO3 at Hanoi is Northern Vietnam region including Hanoi

4.5.2 Climate Effects of BC

Quantitative evaluation of warming effect by SLCP needs comprehensive climate model and is beyond this study

Temperature variation of each air parcel can be estimated from net balance of atmospheric heating and cooling rates by climate factors

Ramachandran and Kedia (2009) calculated the atmospheric heating rate by BC with a radiation model, and performed its values are proportional to the BC mass concentration

68 BC concentrations observed at Hanoi was averagely μg/m3, and often increased to the range of 5-10μg/m3, this implies that BC could increase the atmospheric heating rate of 0.2-1.5 K/day

Figure 4.12. Atmospheric heating rate of BC

(Source: Ramachandran and Kedia, 2009)

This study suggests major part of BC at Ha Noi has been originated from Northern Vietnam region, implying that we can expect mitigation measures for BC emission in Vietnam are effective to reduce atmospheric heating considerably

69 Figure 4.13. BC concentration in Tokyo have decreased time by stringent

regulations for PM emissions (Source: Kondo et al., 2012)

Figure 4.14. The differences between the prior and posterior anthropogenic BC emissions for April and October 2006, using OMI_GC AAOD_BC as the

observation

66 CHAPTER CONCLUSION

“Greatness = Conscience + Discipline”

James Clear. The simultaneously observed data of BC, TO3 and PM2.5 in Hanoi and trajectory analysis from this research indicated that SLCPs in Hanoi and North of Vietnam are impacted significantly by local/regional sources rather than remote sources from surrounding countries Monthly averaged concentrations of BC and PM2.5 were in range of 1-3 μg/m3 and 18-65 μg/m3, respectively BC concentration was estimated from 4% to 6% of PM2.5 in all seasons of 2019 Both BC and PM2.5 were remarkably increased during rush hours or night-time in diurnal variation In contrast, TO3 was often high at noon and depleted to zero at night The climax episodes of BC and PM2.5 were observed in wintertime, especially in January with periods lasting from day to week These high rises were mostly associated with winter monsoon trajectories from South China Sea, which actually transported emissions from North East region of Northern Vietnam

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70 APPENDIX

(AQICN.org) https://doi.org/10.1016/j.scitotenv.2006.04.004 https://doi.org/10.13044/j.sdewes.d6.0218 96629 https://doi.org/10.1371/journal.pone.0196629 https://doi.org/10.1016/j.atmosenv.2010.06.058 https://doi.org/10.1175/2007JCLI1777.1 10.1080/02786826.2017.1375078 https://doi.org/10.1002/jgrd.50348 https://doi.org/10.1016/j.apr.2017.12.001 4 https://doi.org/10.1016/j.atmosenv.2018.04.020 https://doi.org/10.1002/2013JD020824 https://doi.org/10.1002/2015JD024326