COMPARISON OF CONCENTRATION OF CRITERIA AIR
POLLUTANTS AMONG THREE CAMS OF DHAKA CITY
S. R. Islam1, S. A. Shorno2 & M. A. Ali3
1 Department of Civil Engineering, AUST, Bangladesh, e-mail: rakibislam1404@gmail.com
2 Department of Civil Engineering, AUST, Bangladesh, e-mail: afrinshorno@gmail.com
3 Department of Civil Engineering, BUET, Bangladesh, e-mail: mashrafali88@gmail.com
*Corresponding Author
ABSTRACT
Poor air quality is a major concern in Dhaka city. In Dhaka, DoE has three Continuous Air Monitoring Station (CAMS) located at Sher-e-Bangla Nagar (CAMS-1), Farmgate (CAMS-2) and Mirpur (CAMS-3) where concentrations of “criteria pollutants” are measured. Recorded data show that ambient concentrations of PM and NO2 significantly exceed the standards during dry-season; others meet the national standards. Although air quality recorded at the three CAMS show similar trend, there are some noticeable differences. During 2012 to 2017, peak monthly average concentrations of PM2.5
during dry-season in Sher-e-Bangla Nagar, Farmgate and Mirpur were 180 µg/m3, 170 µg/m3 and 200 µg/m3 respectively; while those for PM10 were 255 µg/m3, 290 µg/m3 and 305 µg/m3 respectively. One of the main reasons for high PM concentration during the dry season is the seasonal operation of brick kilns situated along northern to western periphery of the city which is slightly higher in Mirpur area possibly due to its close proximity to brick kiln clusters. Concentration of NO2 has been found to be higher in Farmgate due to vehicular emission. At all three CAMS, the peak PM2.5 concentration shows slightly downward trend, possibly because of improvement of brick-kiln technologies and increasing use of CNG fuel.
Keywords: Air quality; Criteria pollutants; CAMS; Particulate Matter (PM); Seasonal variation.
INTRODUCTION
Dhaka is the capital of Bangladesh with a growing population of about 19 million. The hub for financial and cultural activities of the country, it is one of the most densely populated areas in the world with a density of about 23,000 people per square kilometers within a total area of 300 square kilometers.
Therefore, results in heavy traffic congestion along with industrial growth. Industrial growth was rose to 7.5% in the fiscal year 2011 (Bangladesh Bank, 2011). Emission of different hazardous substances like particulate matter (PM2.5, PM10), some gases such as ozone (O3), oxides of sulfur (SO2), nitrogen (NO2) and carbon (CO), some heavy metal (lead, cadmium, mercury) at elevated level deteriorate the air quality of Dhaka city. At present, the air quality of Dhaka has been ranked as a 3rd most polluted city in the world (WHO, 2018). Air pollution inhibits the sustainable development of Dhaka as well as Bangladesh. The objective of the present study is to observe the trends of concentration of criteria pollutants and to compare these values among three CAMS in Dhaka city.
METHODOLOGY
The trend analysis is based on the air quality data collected from DoE (Department of Environment).
The CAMS measures concentrations of CO, SO2, NO2, O3, CH4 and non-methane hydrocarbon by using multiple gas analyzers. 24-hr average concentrations of PM2.5 and PM10 are also measured at the CAMS using high volume PM10 and PM2.5 samplers. Hourly data of NO2, SO2, CO, O3, daily and monthly data of PM2.5 and PM10 are available from April 2002. The PM10 concentrations have been divided into two size fractions, PM2.5 and PM2.5-10 (= PM10 – PM2.5) for this study. Data of last decade is taken to study the Paper ID: 161
Proceedings of 2nd International Conference On Research and Innovation in Civil Engineering (ICRICE 2020) ISBN: 978-984-3- 8047-7
trend of air quality. Monthly average concentration of criteria pollutants of three CAMS are compared and evaluate the quality with respect to national standard.
RESULTS AND DISCUSSIONS
Among six criteria pollutants Sulfur dioxide is emitted from fuel combustion in power plant and other industries. The contribution of transportation in sulfur dioxide emission is comparatively low because sulfur content of gasoline is relatively low. The concentration of sulfur dioxide in air is not a major concern like ambient particulate matter as its concentration is well below the NAAQS (2005) which is 140 ppb.
[Fig. 1]: Monthly average concentration of Sulfur Dioxide (24 hour) in Dhaka city.
Carbon Monoxide is emitted mostly from transportation. The other sources are industrial process, miscellaneous burning and natural activity like volcanic eruption. The concentration of carbon monoxide in the air of Dhaka city is well below the NAAQS (2005), which is 35 ppm. So, carbon monoxide is not critical pollutant of air pollution of Dhaka city.
[Fig. 2]: Monthly average concentration of Carbon Monoxide (24 hour) in Dhaka city.
Nitrogen dioxide is emitted from fuel combustion in power plants, heating plants and vehicles. It is also emitted from industrial processes like nitric acid plant. The trend of concentration of nitrogen dioxide in Dhaka city is a bit irregular and in many cases it exceeds the NAAQS (2005), which is 53 ppb.
[Fig. 3]: Monthly average concentration of Nitrogen Dioxide (24 hour) in Dhaka city.
The concentration of ambient particulate matter in different regions of Dhaka city is more or less same.
From the table-1, it is clear that the ambient 24-hour average PM2.5 concentration of Darussalam, Mirpur from 2013 to 2017 was slightly higher than Sher-e-Bangla Nagar and BARC Farmgate area because of larger emission sources like higher motorization rate and larger population are found here.
On the other hand, a massive surge in the number of brick kilns situated near this area. About 60% of PM2.5 comes from brick kilns in Dhaka city. It was also seen from previous studies that the PM concentrations in winter to some extent influenced by the transboundary movement of air pollution.
Therefore, emission of PM2.5 from Brick kiln also pollutes the air of nearby locations like Gabtoli, Darussalam road and so on.
Table 1: Yearly average concentration of PM2.5 in three locations of Dhaka City (2013-2017).
Year Sher-e-Bangla Nagar Farmgate Mirpur
2013 81.6 85.7 90.2
2014 72.6 130 96.8
2015 78 78.3 88.4
2017 61.8 77 83.8
The comparison of the monthly average concentration of PM2.5 and PM10 (24-hour) of Sher-e-Bangla Nagar area, Farmgate area and Mirpur area is shown in Fig- 4 and Fig- 5 respectively.
[Fig. 4]: Comparison of monthly average concentration of PM2.5 in different regions of Dhaka.
From figure 5 it can be observed that, the peak concentration of PM10 near CAMS-2 (Farmgate region) and CAMS-3 (Mirpur region) increases slightly in comparison to previous year probably due to increase of motorized-vehicle. As we have some missing data, the graph has some pseudo-peak, but similar pattern is observed among the three stations.
[Fig. 5]: Comparison of monthly average concentration of PM10 in different regions of Dhaka.
CONCLUSIONS
The trend of all criteria pollutants show a sinusoidal variation, which increase during dry season and decrease during rainy season. The peak concentration of PM2.5 shows slightly downward trend which may occurs due to improvement of brick kiln technologies and increasing use of CNG fuel. The concentration of PM2.5 is slightly higher in Mirpur area than other regions of Dhaka city possibly because of its close proximity to brick kiln clusters and ongoing infrastructure development activities.
The concentration of SO2 and CO is well below the NAAQS in all seasons whereas the concentration of NO2 exceeds NAAQS during dry season and thevehicular emission in the busy Farmgate intersection is probably responsible for slightly higher NO2 concentration in that area.
ACKNOWLEDGMENTS
The authors would like to express their deepest gratitude to the Department of Environment, for providing required data.
REFERENCES
ADB and CAI-Asia (2006), Country synthesis report on Urban Air Quality Management- Bangladesh, Discussion draft, Asian Development Bank and The Clean Air Initiative for Asian Cities (CAI-Asia) Center.
AQMP, Department of Environment, Air Quality Data, Agargaon, 2012-2017.
AQMP, Department of Environment, Air Quality Data, Farmgate, 2012-2017.
AQMP, Department of Environment, Air Quality Data, Mirpur, 2012-2017.
Bangladesh Bank (2011), Major economic indicators; Monthly update. Dhaka: Bangladesh Bank.
World Bank (2018), Enhancing opportunities for clean and resilient growth in urban Bangladesh:
Country environment analysis 2018, World Bank, Dhaka, Bangladesh.
