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

MASTER’S THESIS


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

Hanoi, 2020


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

Do Duy Tung

i


TABLE OF CONTENTS
PLEDGE .................................................................................................................... i
LIST OF TABLES .................................................................................................. iv
LIST OF FIGURES ..................................................................................................v
LIST OF ABBREVIATIONS................................................................................ vii
ACKNOWLEDGEMENT .................................................................................... viii
ABSTRACT ............................................................................................................. ix
CHAPTER 1. BACKGROUND AND OBJECTIVES ...........................................1
1.1 Definition of SLCPs and their significance .......................................................2
1.2 Definition of BC, TO3 and PM2.5 and their significance ...................................8

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 2. 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 3. RESULTS ........................................................................................43
3.1. Observed SLCPs’ Concentrations and Their Variation .................................43
3.1.1 Winter........................................................................................................45
3.1.2 Spring ........................................................................................................47
3.1.3 Summer .....................................................................................................48
ii



3.1.4 Autumn ......................................................................................................49
3.2. Seasonal Features of Trajectories ...................................................................53
CHAPTER 4. 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 5. CONCLUSION ...............................................................................66
REFERENCES ........................................................................................................67
APPENDIX ..............................................................................................................70

iii


LIST OF TABLES
Table 1.1. Key features of SLCPs compared with CO2 ................................................. 6
Table 2.1 Diurnal Analysis of BC, O3 and PM2.5 concentration in Hanoi ................. 39

Table 2.2.2 Evidences for distinguishing local/remote source influences ................... 40

iv


LIST OF FIGURES
Figure 1.1. Critical air polluted condition in Hanoi by open biomass burning..........1
Figure 1.2. Global annual mean distribution of BC direct radiative forcing at TOA 3
Figure 1.3. Radiative Forcing Caused by Human Activities Since 1750 ..................3
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 .....................................9
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
.......................................................................................41
Figure 2.11. Screenshot of monitoring portal of AQICN website 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
meteorological data in summer 2019 ........................................................................49
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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 3 time by stringent
regulations for PM emissions ....................................................................................69
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. ...............................................................................................................69

vi


LIST OF ABBREVIATIONS
BC
DRF
HFCs
NMHC
NMVOC
PM2.5
RS
SLCPs
TO3
TOA
UFP

UV

Black Carbon
Direct Radiative Forcing
Hydrofluorocarbons
Non-methane Hydrocarbon
Non-methane Volatile Organic Compounds
Particulate Matter 2.5
Remote Sensing
Short-lived Climate Pollutants
Tropospheric Ozone
Top of the Atmosphere
Ultra-Fine Particle
Ultra-Violet

vii


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.
My appreciation and gratefulness go to JICA, Vietnam - Japan University, Ibaraki
University and Vietnam National University of Forestry for their support to set up
instruments and implement SLCP monitoring systems in Hanoi.

viii



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 1 day to 1 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.
Given the significant climate forcing of BC, this study strongly suggests that
mitigation measures to reduce BC in Vietnam can considerably improve both
regional climate change and air quality in the Northern Vietnam region.

ix



CHAPTER 1. 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.
Figure 1.1. Critical air polluted condition in Hanoi by open biomass burning
1


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).
Until today, SLCP is still an unfamiliar topic and remains underrated in Southeast
Asia, and in particular Vietnam. Recently, PM2.5 from biomass burning,
transportation and thermal power plants have been taken into serious consideration
by localities due to its direct impacts to human health. However, the link between
SLCPs, especially black carbon and tropospheric ozone, with climate change issues
2


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)

TO3
Other

aerosols

BC

Figure 1.3. Radiative Forcing Caused by Human Activities Since 1750
(Source: EPA, 2016)
3


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.
Figure 1.4. Model of CO2 and SLCP cuts compared with other pathways until 2100
(Source: Allen, 2015)

4


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 do 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).
Therefore, it will be too late if mitigation is delayed. An integrated multiple-benefits
approach enables ambitious action by maximizing multiple-benefits and avoiding
negative trade-offs since climate change, air pollution, and sustainable development
are inter-linked (CCAC, 2014).

5



Table 1.1. Key features of SLCPs compared with CO2
RF
RF
Agents (W/m2)

BC

TO3

Lifetime in
the
atmosphere

Main Sources

Environmental
Effects

Fossil fuel combustion Health: carrier of
+0.60
(40%), biomass
toxic chemicals to
(best
4-12 days
burning (40%), biofuels the human body as
estimated)
(20%)
PM2.5


+0.35

Hours Weeks

Health:
Cardiovascular,
Respiratory
diseases

Precursor pollutants
(CO, CH4, NMVOC, NOx)
Agriculture:
after photochemical
reduction of crop
reaction
yield by damaging
ability to absorb
CO2

+0.48

12 years

Agriculture as a key
factor contributing
40% globally

HFCs

+0.32


Up to 29
years

Refrigerator, airconditioning, foam
agents, solvents

Reduction of
stratospheric O3

CO2

+1.66

200 years

Fossil fuel and
industrial processes

Ocean acidification

CH4

Increase of TO3

(Source: Bond et al., 2004; IPCC 2007; UNEP and WMO 2011; CCAC)
Co-benefits of SLCPs’ cut will avoid negative trade-offs, since climate change, air
pollution and sustainable development are inter-linked in it. Recent scientific
assessments coordinated by the UN Environment Programme (UNEP) have
identified several “win-win‖ or synergy measures for near term climate protection

6


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).
If fully implemented by 2030, these measures could reduce global methane

emissions by about 40% and BC emissions by about 80% relative to a “reference‖
scenario (UNEP & WMO 2011).

7


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

areas, reducing albedo effect and causes human health problems as well.

8


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 copollutant 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.

In terms of health effect, BC may cause cancer and has effects on cardiovascular
system (WHO, 2013). BC and co-pollutants make up for most of the particulate
matter 2.5 air pollution, one of the leading environmental causes of ill health and
premature death. 3.5 and 3.2 million people die prematurely each year from
exposure to indoor and outdoor PM2.5 pollution, respectively (Lim S. et al. 2012).

9


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)
TO3 is the product of the chemical reactions involving a number of precursor
pollutants as well as volatile natural organics precursor pollutants created by human
activities include carbon monoxide (CO), non-methane hydrocarbons (NMHC) and
nitrogen oxides (NOx), which are largely emitted by cars and other vehicles, fossil
10


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)
To agriculture and forestry, TO3 causes lower crop yield by reducing photosynthesis
activity and by damaging leaves and roots. It also has warming effect by reducing
absorption of CO2 by vegetation.

11



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.)
PM2.5 contains BC which accounts for up to 10% as a key warming effect
component. However, BC is often emitted along with its co-pollutants. Therefore,
PM2.5 also includes other cooling effect component such as sulfate and organic
particles which stem from vegetation and incomplete combustion of coal and oil.

Major sources of PM2.5 are incomplete combustion of coal, oil and biomass from
motor vehicles, thermal power plants, residential burning, burning of (agriculture)

12


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 7 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.
Gatari et al. (2006) sampled and analyzed atmospheric aerosols from seven rural
sites in North of Vietnam, east of Hanoi and stated that coal and heavy fuel oil
combustion were major sources of atmospheric pollutants in the area and that
biomass burning and road transport had a marked influence on regional air quality.
It was also concluded that Pha Lai thermal power plant was the dominant emitter of
coal combustion emission and PM2.5 concentrations were strongly influenced by
seasonal variations.

13


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 2 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.
In general, there has been up to now few studies on SLCPs in Hanoi and Vietnam,
and there are still uncertainties about BC and TO3 especially in the context of
climate change.

14