concentration of different air pollutants in the ambient air

1. Measurement of Ambient Air Pollutants, Sampling And Analysis
Presented by - Aniket B. Chavan
(PhD. Scholar, DT22CIV015)
ID: 29471)

2. CONTENTS
 AIM
 INTRODUCTION
 MONITORING OBJECTIVE
 AIR SAMPLING
 EQUIPMENT
 METHOD OF MEASUREMENT FOR THE SO2, NO2 and PM10
 CONCLUSION
 FUTURE EXTENSION
 REFERENCE

3. AIM
 The main focus of the study is to find the concentration of different air
pollutants in the ambient air
 To make an estimation major air pollutants PM10, SO2 and NO2 at Air
Pollution Lab, VNIT Nagpur.
 Understand the air monitoring and sampling technique.
 To know about related equipment.

4. What Is AmbientAir Pollution Monitoring ?
Monitoring is an exercise to measure ambient air pollution levels in an area.
The data will indicate the status of the quality of air we breathe.
The data, over a long term, allows us to tease out patterns that help support air pollution control policy. These
patterns include, spatial differences in pollution (which areas of the city are more polluted or better) and temporal
differences (is there a pattern of pollution levels during the day and/or over the seasons)
So, while air pollution monitoring itself does not reduce air pollution, it gives us clues on how much is the
pollution, where is the pollution, and when is that pollution.
Using these data trends, we can conclude if our efforts for improving the quality of air are successful and by how
much. If not, do we need to try other options or be more aggressive in our current efforts.
INTRODUCTION

5. Focus Area Usage
Ambient monitoring the whole city or state or
country
Data is used for long-term spatial and
temporal trend analysis; can be used to
determine the merits and the de-merits of an
intervention over time
On-road (mobile)
monitoring
confined to roads and their
immediate vicinity
Data is used for understanding pollution
exposure during commute; specially to
understand the acute health impacts of being
exposed to augmented pollution levels on the
roads
Satellite monitoring the whole city or state or
country
Data is used mostly for annual scale pollution
trend analysis
Emissions monitoring a specific source Data is used to establish the emission rate by
source, by fuel, by technology, and by usage
Basic uses of air pollution monitoring data

6. What is manual air pollution monitoring ?
This is a process in which a
physical sample is collected, which
is then weighed in the lab,
analyzed, recorded, and then posted
for consumption.
What is continuous air pollution monitoring?
This is a process in which except for
periodically taking care of the
monitoring equipment, all the steps
(sampling, weighing, analyzing,
recording, and posting of the data)
are automated.

7. Pollutant Population of Evaluation Area Minimum No. of AAQ Monitoring
Station
SPM (Hi-Vol.) <1,00 000
100 000- 10,00 000
1000 000 – 50,00 000
>5000 000
4
4+0.6 per 100 000 population
7.5 + 0.25 per 100 000 population
12 + 0.16 per 100 000 population
SO2 (Bubbler) <100 000
100 000- 1 000 000
1000 000 - 10 000 000
>10 000 000
3
2.5+0.5 per 100 000 population
6+0.15 per 100 000 population
20
NO2 (Bubbler) <100 000
100 000- 1000 000
>1000 000
4
4+0.6 per 100 000 population
10
CO <100 000
100 000- 5 000 000
>5 000 000
1
1+0.15 per 100 000 population
6+0.05 per 100 000 population
Recommended Minimum Number of Stations, Population-wise (Source: IS : 5182 (Part 14),
2000).

8. Monitoring Objectives
To provide the data required for rational air quality management
Activate air pollution alert
Assess accuracy of air quality models
Assess impacts of air pollution on health and the environment
Assess accumulation of persistent pollutants
Inform the public through reporting
Assess need for pollution control at
current emission level
future emission levels
Assess effectiveness of pollution control
Assess compliance with regulations

9. Which Air Pollutants?
Air pollution occurs when the air contains substances in quantities that could harm the comfort or health of
humans and animals, or could damage plants and materials. These substances are called air pollutants and
can be either particles, liquids or gaseous in nature (Alias M. et al, 2007).
Particulate matter and gaseous emissions of pollutant emission from industries and auto exhausts are
responsible for rising discomfort, increasing airway diseases and deterioration of artistic and cultural
patrimony in urban centers.
Most commonly: suspended particulate matter, PM10, PM2.5, Pb, SO2, NO2,, CO, NH3, NO, non-methane
hydrocarbons, other heavy metals, benzene, polycyclic aromatic hydrocarbons, and other air toxics.

10. Pollutant Time Weighted
Average
Concentration in Ambient Air Method of Measurement
IndustrialArea Residential,Rural
and
other Areas
Sensitive
Area
Sulphur Dioxide(SO2) Annual Average* 80 µg/m3 60 µg/m3 15 µg/m3
1. Improved West and Gaeke Method
2. Ultraviolet Fluorescence
24 Hours Average** 120 µg/m3 80 µg/m3 30 µg/m3
Oxides of Nitrogenas
NO2
Annual Average* 80 µg/m3 60 µg/m3 15 µg/m3 1. Jacob & Hochheiser modified (NaOH-
NaAsO2) Method
2. Gas Phase Chemiluminescence
24 Hours Average** 120 µg/m3 80 µg/m3 30 µg/m3
Suspended
Particulate
Matter (SPM)
Annual Average* 360 µg/m3 140 µg/m3 70 µg/m3
High Volume Sampling (Average flow ratenot less
than 1.1m3/minute)
24 Hours Average** 500 µg/m3 200 µg/m3 100 µg/m3
Respirable Particulate
Matter
(Size less than10µm)
(RPM)
Annual Average* 120 µg/m3 60 µg/m3 50 µg/m3
Respirable Particulate Matter Sampler
24 Hours Average** 150 µg/m3 100 µg/m3 75 µg/m3
Lead (Pb) Annual Average* 1.0 µg/m3 0.75 µg/m3 0.50 µg/m3 AAS Method after sampling using EPM 2000or
equivalent filter paper
24 Hour Average** 1.5 µg/m3 1.0 µg/m3 0.75 µg/m3
Carbon Monoxide(CO) 8 HoursAverage** 5.0 mg/m3 2.0 mg/m3 1.0 mg/m3
Non dispersive Infrared Spectroscopy
1 HourAverage 10.0mg/m3 4.0 mg/m3 2.0 mg/m3
Ammonia (NH3) Annual Average* 0.1 mg/m3 -
24 HourAverage** 0.4 mg/m3
* Annual Arithmetic mean of minimum 104 measurements in a year twice a week 24 hourly at uniform interval.
** 24 hourly/8 hourly values should be met 98% of the time in a year. However, 2% of the time, it may exceed but not on two consecutive days.
NATIONAL AMBIENT AIR QUALITY STANDARDS (NAAQS)

11. What is Air Sampling ?
A means of collecting contaminates from air to identify and quantify the concentration of the contaminates.
Typically we need to concentrate the contaminates with some sort of media. The exceptions is when we take “whole air
samples” then the concentration step takes place in the lab.
Concentration are calculated in either dimensionless terms:
ppm or ppb or
Concentrations are calculated in mass per volume terms:
µg/m3or mg/m3

12. Why we take Air Samples?
 To identify & measure air pollutants.
 To monitor personal exposures to chemicals.
 To assess the environmental impact of manufacturing
processes.
 To comply with government regulations.
 To identify the source of the pollutants.
 To evaluate the effectiveness of engineering controls
(i.e., ventilation)

13. Air Sampling - The 3 Factors
When taking air samples - there are three factors in determining the concentration
1) Sampling Rate – Active Samplers – Requires a pump to control the flow rate – Passive Sampler –
Design of the sampler dictates the flow rate “it’s fixed” by diffusion
2) Sampling Time – How long of a sample do we need?
3) Sample Volume – The sample volume is calculated by multiplying the flow rate x sampling time:
Flow Rate x Sampling Time = Sample Volume
Note: sample volume is dependent on the temperature and pressure during sampling, so correction is
normally required

14. Respirable dust sampler is an machine designed for the sampling and collection
of dust and NO2 and SO2 by an attached gas manifold. The unit separates
Particulate matter by size, passing small particulate matter to filter paper and
retaining the non respirable particulate matter in a cup. It collects air at rate of
1132 lpm speed.
Major Parts Of Respirable Dust Sampler
I. Main housing :- Metallic body enclosing various parts.
II. Filter holder :- the filter holder assembly consists hopper assembly to hold
filter paper of size 8×10 inches.
III. Manometer :- The flow rate is monitored by it.
IV. Time totalizer :- A time totalizer has been provided to indicate the total time of
sampling in minutes.
Respirable dust sampler was set at about 3 meters height above the ground.
Both the filter papers were set at the respective sockets after moisture removal
inspection and their initial weight was recorded .
Attachments were assembled on the machine.
Glass impinger of the gas manifold was filled with 30 ml each of absorbing
solution for SO2 and NO2 viz. tetra chloro-mercurate ( TCM) solution and sodium
arsenate solution respectively.
Respirable dust sampler
Equipment's

15. filter papers are placed in the machine to collect dust particles.
There are two types of filter papers. Filter paper made up of
glass fiber of size 8×10 (Whatmann 41 GF/A) for the collection
of Particulate matter of size greater than 10 µ. Another Filter
Paper is round having diameter of 47 mm made up of Teflon to
collect PM2.5.
An air desiccator is used by means of moisture removal from the
filter paper. It contains silica gel which absorbs moisture and
turns blue after absorbance
Filter Paper
Air Desiccator

16. A UV visible spectrophotometer was used for analysis of
gaseous samples that is SO2 and NO2.
Ultraviolet-visible spectrophotometry is a technique used to
measure light absorbance across the ultraviolet and visible
ranges of the electromagnetic spectrum. It is used for the
quantitative determination of different analytes or samples
•Electronic weighing machines give precise readings as
compared to manual balances.
•In laboratories small amount of chemicals are needed for
experiments and their weight needs to be accurate.
UV visible spectrophotometer
Electronic weighing machine

17. Guidelines for sampling and analysis of sulphur dioxide in ambient air (Improved West
and Gaeke Method)
(IS 5182 Part 2 Method of Measurement of Air Pollution: Sulphur dioxide).
Preparation of Standards
Measure 0.5 ml, 1.0 ml, 1.5 ml, 2.0 ml, 2.5 ml, 3.0 ml, 3.5 ml and 4.0 ml of working sulphite TCM solution in 25 ml
volumetric flask. Add sufficient TCM solution to each flask to bring the volume to approximately 10 ml. Then add the
remaining reagents as described in the procedure for analysis. A reagent blank with 10 ml absorbing solution is also
prepared. Read the absorbance of each standard and reagent blank
Standard Curve
Plot a curve absorbance (Y axis) versus concentration (X axis). Draw a line of best fit and determine the slope. The
reciprocal of slope gives the calibration factor (CF).
Ml of working sulphite
solution
Concentrat
ion of SO2
(µg/ml of
SO2)
Absorbance
0 0 0.010
0.5 3.34 0.065
1 6.68 0.109
1.5 10.02 0.155
2 13.36 0.193
2.5 16.7 0.252
3 20.04 0.286
3.5 23.38 0.338
4 26.7 0.405
y = 0.0142x + 0.0114
R² = 0.9966
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
0.450
0 5 10 15 20 25 30
Chart Title
Standard curve
CF=
1
𝑠𝑙𝑜𝑝𝑒
=
1
0.0142
= 70.422

18. FLOW CHART FOR MEASUREMENT OF SULPHUR DIOXIDE
Place 30 ml of absorbing media in an impinger
Connect it to the gas-sampling manifold of gas sampling device(RDS/HVS).
Draw air at a sampling rate of 1 lpm for four hours (Qintial)
Check the volume of sample at the end of sampling and record it (Qfinal)
Transfer the exposed samples in storage bottle and preserve
Prepare calibration graph as recommended in method
Take 10/20 ml. aliquot of sample in 25 ml. Vol. Flask
Take 10/20 ml. of unexposed sample in 25 ml. Vol. Flask (blank)
Add 1 ml Sulphamic acid. Keep it 10 minutes
Add 2 ml formaldehyde
Add 2 ml working PRA
Make up to mark (25 ml.) with distilled water.
Keep it 30 minutes for reaction
Set Zero of spectrophotometer with Distilled water
Measure absorbance at 560 nm
Calculate concentration using calibration graph
Calculate concentration of Sulphur dioxide in µg/m3

19. Blank sample + sample analysis of SO2

20. Observation Table For SO2
SR. NO.
ABSORBANC
E (Ab/As)
(As-Ab)
CF =
1/SLOPE
VOLUM
E OF
SAMPLE
EXPOSE
D TO AIR
(VS, mL)
VOLUME
OF
ALIQUOT
TAKEN
FOR
ANALYSI
S (Vt, mL)
FLOW RATE (LPM)
DURATIO
N OF
SAMPLIN
G (MIN)
VOLUME
OF AIR
(Va, M3
)=
(flow rate *
duration of
sampling)/1
000
CONCENTRATION
OF SO2 (µg/M3
) =
(As-
Ab)*CF*Vs/(Va*Vt)
FINAL
CONCE
NTRATI
ON OF
SO2
(µg/M3
)
AVERAG
E
CONCEN
TRATION
OF SO2
(µg/M3
)
INITIAL(Q
intial)
FINAL(Qfi
nal)
FLOW
RATE
(LPM)
Qavg
BLANK Ab= 0.027 0 70.42 20 10 1 1 1 240 0.240 0
1
0.04
0.04-0.027
=0.013
70.42 20 10 1 1.1 1.05 240 0.252 7.27
7.27
8.84
2 0.043 0.016 70.42 20 10 1 1.2 1.1 240 0.264 8.54 8.54
3 0.044 0.017 70.42 20 10 1 1.2 1.1 240 0.264 9.07 9.07
4 0.042 0.015 70.42 20 10 1 1.1 1.05 240 0.252 8.38 8.38
5 0.045 0.018 70.42 20 10 1 1.3 1.15 240 0.276 9.19 9.19
6 0.046 0.019 70.42 20 10 1 1.1 1.05 240 0.252 10.62 10.62
C (SO2) = Concentration of Sulphur dioxide, µg/m3
Vs = Volume of sample, ml
Vt = Volume of aliquot taken for analysis, ml
As = Absorbance of sample
Ab = Absorbance of reagent blank
CF = Calibration factor
Va = Volume of air sampled, 𝑚3
3 s b
2
a t
(A - A ) ×CF×
C (SO , g/m )=
V V
s
V


=
0.04−0.027 ∗70.42∗20
0.240∗10
= 7.27 µg/𝑚3

21. Guidelines for sampling and analysis of Nitrogen dioxide in ambient air(Modified
Jacob and Hochheiser Method)
Modified Jacob & Hochheiser Method (IS 5182 Part 6 Methods for Measurement of
AirPollution: Oxides of nitrogen).
Ml of
working
sulphite
solution
Absorbance
0 0.002
1 0.038
2 0.063
3 0.084
4 0.122
5 0.143
6 0.178
7 0.202
8 0.223
9 0.252
10 0.280
12 0.355
15 0.432
20 0.582
y = 0.0287x + 0.002
R² = 0.9986
0.000
0.100
0.200
0.300
0.400
0.500
0.600
0.700
0 5 10 15 20 25
Chart Title
Preparation of Standards
Pipette 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15 and 20 ml of working standard solution in to 50 ml volumetric
flask. Fill to 20 ml mark with absorbing solution. A reagent blank with 10 ml absorbing solution is also
prepared. Add reagents to each volumetric flask as in the procedure for analysis. Read the absorbance of
each standard and reagent blank against distilled water reference.
Standard Curve
𝐶𝐹 =
1
𝑠𝑙𝑜𝑝𝑒
=
1
0.0287
= 34.843

22. FLOW CHART FOR MEASUREMENT OF NITROGEN DIOXIDE
Place 30 ml of absorbing media in an impinger
Connect it to the gas sampling manifold of gas sampling device(RDS/HVS).
Draw air at a sampling rate of 1 lpm for four hours (Qintial)
Check the volume of sample at the end of sampling and record it (Qfinal)
Transfer the exposed samples in storage bottle and preserve
Prepare calibration graph as recommended in method
Take 10 ml. aliquot of sample in 50 ml. Vol. Flask
Take 10 ml. of unexposed sample in 50 ml. Vol. Flask (blank)
Add 1 ml hydrogen peroxide,
Add 10 ml sulphanilamide
Add 1.4 ml NEDA
Make up to mark (50 ml.) with distilled water.
Keep it 10 minutes for reaction
Set Zero of spectrophotometer with Distilled water
Measure absorbance at 540 nm
Calculate concentration using calibration graph
Calculate concentration of Nitrogen dioxide in µg/m3

23. Sample analysis for NO2 + Blank Sample

24. SR. NO.
ABSORBANCE
(Ab/As)
(As-Ab)
CF =
1/SLOPE
VOLUME
OF
SAMPLE
EXPOSED
TO AIR
(VS, mL)
VOLUME
OF
ALIQUOT
TAKEN
FOR
ANALYSIS
(Vt, mL)
FLOW RATE (LPM)
DURATION
OF
SAMPLING
(MIN)
VOLUME
OF AIR
(Va, M3
)=
flow rate *
duration of
sampling
CONCENTRATION
OF SO2 (µg/M3
) =
(As-Ab)*CF*Vs/(Va*Vt)
FINAL
CONCEN
TRATION
OF SO2
(µg/M3
)
AVERAGE
CONCENT
RATION
OF SO2
(µg/M3
)
INITIAL
(Qintial)
FINAL
(Qfinal)
FLOW
RATE
(LPM)
BLANK Ab= 0.002 0 28.57 20 10 1 1 1 240 0.240 0.00
1
As= 0.18
0.18-
0.002=0.178
28.57 20 10 1 1.2 1.1 240 0.264 46.98
46.98
37.95
2 0.141 0.139 28.57 20 10 1 1.2 1.1 240 0.264 36.69 36.69
3 0.121 0.119 28.57 20 10 1 1 1 240 0.240 34.55 34.55
4 0.125 0.123 28.57 20 10 1 1.1 1.05 240 0.252 34.01 34.01
5 0.132 0.13 28.57 20 10 1 1 1 240 0.240 37.74 37.74
6 0.145 0.143 28.57 20 10 1 1.2 1.1 240 0.264 37.74 37.74
3 s
a t
b
2
s
(A - A ) CF V
C (NO μg/m ) =
V × 0.82 × V
 
Where,
As = Absorbance of sample
Ab = Absorbance of reagent blank
CF = Calibration factor
Va = Volume of air sampled, m3
Vs = Volume of sample, ml
Vt = Volume of aliquot taken for analysis, ml
0.82 = Sampling efficiency
=
0.18 − 0.002 ∗ 28.57 ∗ 20
0.240 ∗ 0.82 ∗ 10
= 46.98 µg/𝑚3
Observation table for NO2

25. Guidelines for sampling and analysis of Particulate Matter (PM10) in ambient
air(Gravimetric Method)
Principle of the method
Air is drawn through a size-selective inlet and through a 20.3 X 25.4 cm (8 X 10 in) filter at a
flow rate, which is typically 1132 L/min.
Particles with aerodynamic diameter less than the cut-point of the inlet are collected, by the filter.
The mass of these particles is determined by the difference in filter weights prior to and after
sampling.
The concentration of PM10 in the designated size range is calculated by dividing the weight gain of
the filter by the volume of air sampled.

26. Filter Paper after sampling
Cup used for the determination of SPM

27. FLOW CHART FOR MEASUREMENT OF PM10
Check the filter for any physical damages
Mark identification number on the filter
Condition the filter in conditioning room / desiccator for 24 hours
Record initial weight ( W1)
Place the filter on the sampler
Run the sampler for eight hours
Record the flow rate on hourly basis
Remove the filter from the sampler
Keep the exposed filter in a proper container
Record the total time of sampling & average flow rate
Again condition the filter in conditioning room / desiccator for 24 hours
Record final weight (W2)
Calculate the concentration of PM in µg/m3
10

28. DATE
S.N. OF
CUP
S.N. OF
FILTER
TIME
TIME OF
FLOW (8 H),
MIN
INITIAL
FLOW
RATE
(M3
/MIN)
FINAL
FLOW
RATE
(M3
/MIN)
AVERAG
E FLOW
RATE
(M3
/MIN)
VOL.
OF AIR
(M3
)=
Avg
flow
rate*
time of
flow
WT. OF CUP (g)
WT. OF
SPM
CONCE
NTRATI
ON OF
SPM
(µg/M3
)
WT. OF FILTER
(g)
WT. OF
PM10
CONCENTRATION (µg/M3
)
INITIA
L
FINAL
INITIA
L (W1)
FINAL
(W2)
RSPM /
PM10
AVERA
GE
TSPM
AVERAG
E
MONDA
Y
16/01/23
B1 1
6 AM TO 2
PM
480 1.1 1.1 1.10 528.00 17.0880 17.1648 0.0768 145.45 2.8360 2.9130 0.0770 145.83
101.16
291.29
165.15
B2 2
2 PM TO 10
PM
480 1.1 1.09 1.095 525.60 18.4800 18.4933 0.0133 25.30 2.8230 2.8760 0.0530 100.84 126.14
B3 3
10 PM TO 6
AM
480 1.1 1.1 1.1 528.00 18.1770 18.1882 0.0112 21.21 2.8280 2.8580 0.0300 56.82 78.03
C (PM) µg/m = (W2 – W1) x 106/ V
Where, C PM10 = Concentration of PM , µg/𝑚3
W1= Initial weight of filter in g
W2 = final weight of filter in g
106 = Conversion of g to µg
V = Volume of air sampled, 𝑚3
𝐶𝑃𝑀10 =
2.913−2.836 ∗106
528
= 145.83 µg/𝑚3
𝐶𝑠𝑝𝑚 =
17.648−17.088 ∗106
528
= 145.45 µg/𝑚3
𝐶𝑃𝑀10 + 𝐶𝑠𝑝𝑚 = TSPM
145.83 + 145.45 = 291.29 µg/𝑚3
Observation table for PM10 & SPM

29. Conclusion
 AQM data provides useful information for identifying sources of pollution.
 Form the analyzed data one can generate AQI which indicates the condition of the air quality of the
surrounding air.
 Pollutant present in the ambient air is a mixture of different local, area, and regional source.
 Concentration varies with time due to metrological factors like temperature, pressure, relative humidity, wind
speed and wind direction.
 Low-cost sensor may be used for the monitoring of gaseous pollutants, to get concentration data at few more
location in the urban area.
 Air Quality monitoring plays a vital role in the development of control measures for the air pollution control.

30. REFERENCES
1. Guidelines for Sampling and Measurement of notified Ambient Air Quality
2. Parameters (NAAQS 2009), Volume-I,CPCB
3. Guidelines for continuous sampling and real time analyses, Volume-II, CPCB
4. IS 5182 Part 2 Method of Measurement of Air Pollution: Sulphur dioxide
5. IS 5182 Part 6 Methods for Measurement of Air Pollution: Oxides of Nitrogen
6. Method 501, Air Sampling and Analysis, 3rd Edition, Lewis publishers Inc.
7. IS 5182 Part 23 Method of Measurement of Air Pollution: Respirable Suspended Particulate Matter (PM )
cyclonic flow technique
8. Method IO-2.1 Sampling of Ambient Air for Total Suspended Particulate
9. Matter (SPM) and PM Using High Volume (HV) Sampler
10. Basics in Air Monitoring Frank Michel, Jamie Brow ,Sigma-Aldrich Co
11. Saravanakumar, R., Sivalingam, S. and Elangovan, S., 2016, “Assessment of air quality index of Coimbatore
City in Tamil Nadu”, Indian Journal of Science and Technology, Indian Society for Education and
Environment, 9, 41, 1-5. 10.17485/ijst/2016/v9i41/99185
12. Pfeiffer R.L., (2005), “Sampling For PM10 and PM2.5 Particulates” - Micrometeorology in Agricultural
Systems, Agronomy Monograph no. 47.
13. http://envirotechindia.com/
14. air pollution monitoring (2023), urban emissions

31. 15. Krishna Prasad Vadrevu, Aditya Eaturu, Sumalika Biswas , Kristofer Lasko , Saroj Sahu , J.
Garg ,Chris Justice, “Spatial And Temporal Variations Of Air Pollution Over 41 Cities Of India
During The COVID-19 Lockdown Period Scientific Reports” 2021
16. Gurjar, B.R., van Aardenne, J.A., Lelieveld, J., Mohan, M., 2004. Emission estimates and trends (1990–
2000) for megacity Delhi and implications. Atmospheric Environment 38, 5663–5681.
17. Nicolas Renard, “Prevention And Control Of Air Pollution In China: A Research Agenda For Science And
Technology Studies” Surveys and Perspectives Integrating Environment and Society, 2015
18. Gurjar B R, Butler T M, Lawrence MG and Lelieveld J, Evaluation of emissions and air quality in
megacities, Atmospheric Environment, 42(7)42(7)42(7)42(7)42(7), 1593-1606 (2008).
19. Guttikunda, S.K., Carmichael, G.R., Calori, G., Eck, C., Woo, J.-H., 2003. The contribution of megacities
regional sulfur pollution in Asia. Atmospheric Environment 37, 11–22.
20. Chan L. Y. and Kwok, W. S: 2001, ‘Roadside suspended particulates at heavily trafficked urban sites of Hong
Kong–Seasonal variation and dependence on meteorological conditions’, Atmospheric Environment 35,
3177–3182.