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Urban air pollution: a Bangladesh perspective
M. Habibur Rahman1 & A. Al-Muyeed2
1Department of Civil/Environmental Engineering,
Bangladesh University of Engineering & Technology, Bangladesh
2Department of Civil/Environmental Engineering,
Dhaka University of Engineering & Technology, Bangladesh
Abstract
This study summaries several monitoring and surveys on ambient concentrations
of NOx, SO2, CO,O3 particulate matters, lead and black smoke which have been
carried out by the authors, Bangladesh Atomic Energy Commission and
Department of Environment (DOE) in Bangladesh. Airborne lead was a major
concern but the phase-out of lead in gasoline implemented throughout South
Asia in the year 1999 and the early 2000s has contributed greatly to reducing the
lead concentration in ambient air. Analysis of the time series air quality data (of
specific air pollutants, NOX, SO2, CO,O3 and particulate matters, for selected
stations from the years 2002 to 2004) indicates that the ambient air of Dhaka
City, the capital of Bangladesh, is polluted more than 55 percent of the year. The
level of pollutants at 49 important road intersections shows the quality of air at
the roadsides of Dhaka City. The air quality index (AQI) estimated at various
locations of the city reveals that more than 70 percent of the roadside
environments are severely polluted and the rest are highly polluted on the basis
of the WHO guideline value. This pollution level at roadside environments is
closely related with the density of motor vehicles plying on the roads. With the
increase in the number of motor vehicles caused by economic growth and
industrialisation, the level of pollution is expected to worsen further in the future.
To improve the situation, proposals for some pollution abatement measures
including the introduction of unleaded gasoline and CNG-powered 3-wheelers
instead of 2-stroke 3-wheelers are critically discussed in this paper.
Keywords: air quality, Dhaka City, particulate matters, gaseous pollutants.
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
Air Pollution XIII 605
1 Air pollution in Bangladesh
Air is a life sustaining precious natural resource. Fresh air is one of the most
indispensable gifts of nature without which human will not survive. And human
activities can be interfered by the pollution of this vital resource. It is only in
recent times that mankind has become aware of the extent to which this
interference is sustainable.
The level of air pollution in many of the developing countries is so bad that it
is being recognized as one of the priority issues. This is an important public
health problem in most of the cities in developing countries. Pollution in the
cities like Bangkok, Cairo, Delhi, Mexico and Dhaka far exceeds the acceptable
limits set by the World Health Organization (WHO). Epidemiological studies
show that air pollution in developing countries accounts for tens of thousands of
excess deaths and billions of dollars of lost productivity every year (Faiz et al.,
1996). In South Asian region, urban air pollution is estimated to cause over
250,000 deaths and billions of cases of respiratory illness every year (WB,
2004). The children are more vulnerable to such situation.
Presently, on any working day, filthy gray haze emits mists from auto
exhausts and chemicals hang lower and lower than ever over the city. The smog
causes the eyes to water, coats lungs with layers of microscopic, noxious soot.
Emissions from all types of automobiles like car, jeep, bus, truck, minibus,
microbus, two- stroke engine driven vehicles (auto-rickshaw, tempo, mini-truck)
and motorcycles have been unabatedly polluting the city's air. Aircraft, railway
engines, industrial plants, power plants, brick fields, open burning incineration,
solid waste disposal sites and dust particles are also contributing to the air
pollution. Dust pollution due to road diggings, constructions arid other
development activities further compound the city's air pollution situation. This
poor air quality threatens human health, structures, and vegetation; lowered
visibility; and, enhanced greenhouse gas emissions. It has been estimated by the
World Bank (WB) that the country could avoid 15,000 deaths and save $200
million to $800 million annually by reducing in cities of Dhaka, Chittagong,
Rajshahi and Khulna (UNEP, UNICEF & WHO, 2002). The yearly costs of
health maintenance due to air pollution in Dhaka City have been estimated in
excess of US$ 100 million and cause more than 8,000 excess deaths in the city.
The loss caused by air pollution and the associated degradation in quality of life
impose a significant burden on people in all sectors but especially the poor. Thus
it attracted growing attention from the industry, government, civil society and the
public at large.
The World Health Organization (WHO) classifies sulfur dioxide (SO2),
nitrogen dioxide (NO2), carbon monoxide (CO), Ozone (O3), suspended
particulate matter (SPM), and lead as key or “classical” pollutants. The same
pollutants are called “criteria” pollutants by the U.S. Environmental Protection
Agency (EPA). Health-based ambient air quality standards are normally set for
the classical pollutants first, and their measurements are examined to judge the
magnitude of the air pollution problem. In Bangladesh perspective, this study
summaries several monitoring and surveys on ambient concentrations of NOx,
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
606 Air Pollution XIII
SO2, CO, O3, particulate matters, lead and black smoke have been carried out by
the authors, Bangladesh Atomic Energy Commission and Department of
Environment in Bangladesh. It also investigates the level of air pollution on the
basis of air quality index (AQI), assess its consequences on human health. The
result of this study will assist decision-maker in formulating national policies to
combat air pollution.
2 Traffic volume in Dhaka city
Dhaka, which is both the nation's administrative capital and business hub, has a
total estimated population of more than nine million and it is projected to swell
to 16 million by the year 2015, making it the seventh largest populous city in the
world. This overcrowded city is already considered as one of the world’s most
polluted urban centres and it has the highest volume of traffic comparing to other
cities of Bangladesh so that Dhaka has the prime attribute of air pollution in
Bangladesh. The Figure 1 represents the increasing trend of no. of vehicles in
each year of Dhaka City. It is apparent from the Figure 1, as of 2001 an
estimated total of 168,718 automobiles are on roads of Dhaka, has heterogeneous
traffic flows. A substantial part of total traffic is non-motorized vehicles enhance
severe congestion and pollution problem especially in road intersections. Around
80% of total trips in Dhaka city is comprised of non-motorized transport (NMT)
and only 5.9% trips are made by motorized transport (MT). Average trip length
of MT is 27 minutes. Trips made by public transport specially buses are very
low, only 0.9%. The maximum trips of vehicle modes are made by using
rickshaws are 43%. Though it is very difficult to quantify pollution contribution
from such heterogeneous traffic combinations, the influence of NMT on
pollution are averaged upon the pollution considering the average speed of traffic
flows. Based on data from different sources and road surveys conducted by the
authors the traffic pollution contribution in Dhaka city has been assessed and
presented in the following sections.
3 Air particulate matters and gaseous pollutants
To satisfy the basic national need for monitoring air quality and to control air
pollution in the major cities of Bangladesh, Department of Environment (DOE)
set up the first ever in the country, the Continuous Air Quality Monitoring
Station (CAMS) in 2002 in the open space of the most important public
institution of Bangladesh, the Parliament Buildings, in the centre of the Dhaka
city. Twenty-four hour average, monthly measurements of PM10 and PM2.5
particulate matters, collected over the period of 22 months are illustrated in
Figure 2. The systematic trend observed in these data is the peaking of the
concentrations from October to April beyond which the concentration of both
PM10 and PM2.5 are decreasing due to rain out effect. The other time-series data
for PM2.5 have been collected at two sampling sites: Farm Gate (Figure 3) which
faces an intersection of several major roads, and a semi-residential site located
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
Air Pollution XIII 607
about 50 meters from a road with moderate traffic (Figure 4). These Figure 3 & 4
(WB 2004) show the seasonal pattern observed throughout the year; high
particulate concentrations in winter when it is dry and when low temperatures
cause thermal inversion whereby pollutants are trapped near ground level, and
low concentrations during the rainy season. There is a considerable fall in PM2.5
concentrations at the Farm Gate between 2002 and 2003. As discussed below,
this could be in part due to the ban on all existing two-stroke engine three-
wheelers that went into effect on January 1, 2003 by promoting the vehicles that
use compressed natural gas (CNG). The average PM2.5 concentrations for the
month of January in 2001 and 2002 were 87 and 136 µg/m3 (before the
phaseout), respectively, compared to 55 and 54 µg/m3 in 2003 and 2004,
respectively (after the phaseout). The monthly concentrations were 125, 75 and
74 µg/m3 in December for 2000, 2001 and 2002 (before the phaseout) and 44
µg/m3 in 2003 (after the phaseout).
Figure 1: Motorized Vehicles on Road in Greater Dhaka.
Figure 2: Monthly 24 hr Average of PM concentration at CAMS, Sangsad
Bhaban.
Av g PM 2.5 and PM 10
0
50
100
150
200
250
300
Apr, 02
Jun, 02
Aug, 02
Oct, 02
Dec, 02
Feb, 03
Apr, 03
Jun, 03
Aug, 03
Oct, 03
Dec, 03
Month
PM2.5 and PM10 in
micrograms per cubic meter
PM10
PM2.5
M otorized Vehicle of Dhak a City
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
Year
No. of Vehicle
Motorized Vehicle of
Dhaka C ity
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
608 Air Pollution XIII
Figure 3: 24 hour Average PM2.5 Data at Farm Gate, Dhaka, Bangladesh.
Figure 4: 24 hour Average PM2.5 Data at Semi-Residential Area, Dhaka.
Av g NOx & SO x
0
50
100
150
200
250
300
Months
Avg Nox
SO2 *0.1
Figure 5: Monthly 24 hr Average of NO
2
& SO2 concentration at CAMS,
Sangsad bavan.
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
Air Pollution XIII 609
The monthly average of SO2 and NO2 in ppb are Figure 5. The level of CO
during this monitoring period had the value range from 0.2 to 2.0 ppm which has
been shown in Figure 6
Avg C O
0
0.5
1
1.5
2
2.5
3
Apr, 0 2
May, 0 2
Jun, 02
Jul, 02
Aug, 02
Sep, 02
Oct, 02
Nov, 02
Dec, 02
Jan, 03
Feb, 03
Mar, 0 3
Apr, 0 3
May, 0 3
Jun, 03
Jul, 03
Aug, 03
Sep, 03
Oct, 03
Nov, 03
Dec, 03
Jan, 04
Month
CO in ppm
Avg CO
Figure 6: Monthly 1-hr Average CO at CAMS, Sangsad Bhaban.
During the monitoring period, very few measurements of ozone were made
above the detection limit of the method. The maximum value of 299 ppb was
observed in December 2002, for an hour average, as one event only, against the
proposed Bangladesh standard of 120 ppb. It is clear from the Figures 2, 3 and 4
that the levels of PM from October 2002 to March 2003 exceeded the
Bangladesh Air Quality Standard (Table 1) in high volume traffic area having
maximum concentration of 271 µg/m
3
in Jan’03 while the SO
2
levels exceed the
standard during the dry winter season (December 2002 to March 2003) having
maximum concentration of 19.5 ppb in December 2002. The NOx levels appear
to be below the acceptable limit defined by the air quality standard. It should be
borne in mind that Bangladesh Standards are not directly comparable with
international air quality standards because of differences in averaging time.
However, in general terms, PM and SO
2
concentrations exceed US standard and
WHO guideline (Table 1) of ambient air quality during whole year in Dhaka.
The Bangladesh Atomic Energy Commission measured 14.6 µg/m
3
of Pb in
ambient air in Dhaka over the period November 1995 to January 1999 (Biswas et
al., 2003), whereas the WHO guideline (1 year average) for Pb in air is 0.51
µg/m
3
. The Table 2 represents the concentration of Pb in different periods of the
year. It can be observed that the yearly average Pb concentrations in the ambient
air have declined by approximately two-thirds from their earlier values after the
introduction of unleaded gasoline.
The effect of unleaded gasoline introduction can be seen from Figure 7, is the
plot of the monthly average of the ratio of Pb and Black Carbon (BC) % as a
function of time. This ratio is a weather independent estimate of Pb
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
610 Air Pollution XIII
concentration. Two steps of Pb reduction can be seen in this Figure 7. The first
reduction occurred around October 1998. This is probably the effect of making
regular gasoline Pb-free earlier in July. The concentration started increasing
again, probably because of increased consumption of leaded-premium gasoline.
Although the high-octane unleaded gasoline was introduced in July 1999, the
reduction of the Pb concentration in air could be seen only after October. This
lag phase could be caused by old leaded stock or a contaminated distribution
system. This time, the ratio appears to be steadily dropping, which is consistent
with a fully unleaded supply system.
Table 1: Comparison of air quality standards, ambient air quality in
Bangladesh.
Pollutant Average
Time
WHO
Guideline
US
Standards
Bangladesh
Standards
Ambient
Concentration in
Dhaka
1 hour 30 mg/m3 9 ppm
10 mg/m3
CO
Carbon
monoxide 8 hour 10 mg/m3 35 ppm
40 mg/m3
11 ppm
(instantaneous
average)
24 hour 0.5-1. µg/m3 4.63 µg/m3 Pb
Lead Quarterly 1.5 µg/m3
Annual 0.053 ppm
100 µg/m3
80 µg/m3
(Residential) 100
µg/m3 (Commercial)
41.8 µg/m3 NO2
Nitrogen
dioxide 24 hour 150 µg/m3 0.063 ppm
119 µg/m3
O3
Ozone
1 hour 150 - 200
µg/m3
0.12 ppm
235 µg/m
Annual 60-90 µg/m3 50 µg/m3 200 µg/m3
(Residential)
400 µg/m3
(Commercial)
1245-1601 µg/m3
(Commercial)
445 µg/m3 (Residential)
PM10/TSP/S
PM
24 hour 150-230
µg/m3
150 µg/m3
Annual 40-60 µg/m3 0.03 ppm
80 µg/m3
80 µg/m3
(Residential) 100
µg/m3 (Commercial)
472.9 µg/m3
(Commercial) 63.5 µg/m3
(Residential)
SO2
Sulfur
dioxide
24 hour 100-150
µg/m3
0.14 ppm
365 µg/m3
Source : www.eng-consult.com/air/standard.html.
Table 2: Changes in Pb concentration in Dhaka city.
Period Pb (Before 1996)
ng/m3
Pb (After Oct. 1999)
ng/m3
Comments
Low Rainfall Period(LRF)
November – January
463 212 Average over LRF
months
Medium Rainfall
Period.(MRF)
February-May, September-
October
253 170 Average over MRF
months
High Rainfall Period.(HRF)
(June – August)
160 66 Average over HRF
months
Average 312 106 12 months
Source : Biswas, et al, 2003.
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
Air Pollution XIII 611
Figure 7: Average Monthly Pb/BC % ratios vs. time for July1997-January
2001 Source: Biswas, et al, 2003.
Besides government information, there are several independent researchers’
data available from the mid to late 1990’s on CO monitoring, NOx concentration
in selected urban intersections Dhaka, PM measurements at DOE’s Agargaon
office and the rooftop of World Bank office. These data are listed in Table 1 and
compared with local and international ambient air quality standards. All
measured data exceed Bangladeshi and/or international standards. Again, it is
evident from the Figures 2 to 6 that from the late October to late April, this 6 to 7
months are the most air-polluted period in a year, which comprises more than 55
percent of days of a year.
4 Air quality index
On the basis of the observed data and the proposed air quality standards, some
calculations have been performed to provide some air quality index (AQI)
numbers so that the public understanding of the air pollution problems becomes
clear. The index is calculated on the basis of Air Quality Rating for each of the
pollutants which is defined as the ratio between the observed level of the
pollutant in the air and the allowable limit for the same expressed in percentage.
For a number of pollutants, AQI is obtained from the geometric mean of the Air
Quality Ratings. Based on the Air Quality Index, the categorization of ambient
air environment is presented in Table 3 (Alam et al, 1999). Hereafter, AQI’s
have been calculated using ambient concentration of CO, NO2 and SO2 measured
at 49 important roadside intersections of Dhaka city (Alam et al, 1999) on the
basis of the permissible level of the concentrations provided by both WHO and
DOE, Bangladesh. The results are summarized in Table 4. It is observed that if
AQI is calculated on the basis of WHO standards, in 70% of the areas the
roadside environment is severely polluted and 30% of the areas is heavily
polluted. For the standards set by the Government of Bangladesh, all the areas
are very severely polluted. The most highly polluted areas are Mohakhali,
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
612 Air Pollution XIII
Jatrabari and Panthopath where the AQI is above 200 (Based on WHO
guideline). Even at roads besides residential areas like Dhanmondi and Jigatola
the AQI is above 100. Again, according to US-EPA model, AQI has been
calculated using single pollutant as parameter from the data of Sangsad Bhaban.
The Figure 8 shows that the average AQI is 100 or more than 100 throughout the
year. According to US-EPA model (www.epa.gov), the pollution represents
Unhealthy for Sensitive Groups, which include national monuments, health
resorts, hospitals, archeological spots and educational institutions.
Table 3: Categories of Ambient Environmental Quality on the basis of AQI.
Categories AQI Description
I Less than 10 Very Clean
II 10-25 Clean
III 25-50 Fairly Clean
IV 50-75 Moderately Polluted
V 75-100 Polluted
VI 100-125 Heavily Polluted
VII More than 125 Severely Polluted
Table 4: Air quality levels in the roads of Dhaka City.
Standard Category of Air Quality Range of the
Estimated
Value of AQI
Average
AQI for the
Category
Number of
Locations in the
Category
AQI calculated on the
basis of Bangladesh
Standard
Severely Polluted 209-454 318 49 (100%)
Severely Polluted 131-215 167 34 (70%)
Heavily Polluted 102-124 114 14 (30%)
AQI calculated on the
basis of WHO Standard
Polluted 99 - 1
Figure 8: Average AQI measured at CAMS, Sangsad Bhaban.
5 Conclusion
Air pollution in Dhaka is a high priority concern as it is seriously affecting the
quality of life in the city and represents a major public health issue Although
pollutants emitted from the transport sector clearly constitute the major pollution
problem in Dhaka, no emission inventory detailing sources of pollution is
Average A Q I at CA M S , Sangs ad Bhaban
0
50
100
150
200
250
300
Apr, 02
Jul, 02
Oct, 02
Jan, 03
Apr, 03
Jul, 03
Oct, 03
Jan, 04
Month
AQI value
AQI
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
Air Pollution XIII 613
currently available. The study shows that seventy percent of the roadsides of the
city are severely polluted. Its consequence on the health of the city dwellers is
very concerning. The ambient levels of PM, SO2, Pb far exceed the Bangladesh
air quality standards and WHO guidelines, resulting pollution, which comprises
more than 55 percent days of a year. There is also evidence that ambient NO2
concentration regularly below the acceptable limit defined by the air quality
standard. Although there is a lack of time-series data, the air quality
measurements available indicate that Dhaka’s air pollution is worsening. Some
positive steps like replacement of 2-stroke 3 wheelers by CNG powered 3-
wheelers and introduction of unleaded gasoline have improved the quality of air,
but still lack of regular monitoring and examining of emission from motor
vehicles, limited no. of streets comparing to increasing volume of traffic, lack of
management of traffic system hamper the quality of air immensely, which must
be addressed and assessed accordingly.
References
[1] Alam M.J.B et al (1999), Ambient Air Quality at Roadside in Dhaka City,
Journal of pollution Research, Enviromedia, India, Vol 1999(2).
[2] Biswas et al (2003), Impact of Unleaded Gasoline Introduction on the
Concentration of Lead in the Air of Dhaka, Bangladesh, Journal of Air &
Waste Management Association, Vol 53, 1355-1362.
[3] Faiz, A., Weaver, C. S. and. Walsh, M. P. (1996), Air Pollution from
Motor Vehicles: Standards & Technologies for Controlling Emissions,
WB, USA.
[4] http://www.eng-consult.com/air/air.htm.
[5] http://www.epa.gov.
[6] UNEP, UNICEF & WHO (2002), Children in the New Millennium:
Environmental Impact on Health, United Nations Environmental
Programme, United Nations Children’s Fund and World Health
Organization.
[7] World Bank (WB) (2004), http://www.worldbank.org/sarurbanair.
©2005 WIT Press
WIT Transactions on Ecology and the Environment, Vol 82,
www.witpress.com, ISSN 1743-3541 (on-line)
614 Air Pollution XIII