Characteristics of the air pollution in the city of Dhaka, Bangladesh in winter
Introduction
Atmospheric pollution in urban area is a major issue in many developing countries all over the world. Sulfur dioxide (SO2) and nitrogen dioxide (NO2) are major pollutants in the ambient atmosphere because of their adverse effects on human health and vegetation, their contributions to the acidification of the environment (Rodhe, 1989; Legge and Krupa, 1990) and the role of NOx in the formation of photochemical oxidants. NOx contributes to the build-up of tropospheric ozone (O3) and to the change of the concentration of hydroxyl radical (OH) which determines the lifetime of reactive greenhouse gases (Houghton et al., 1990), and thus is also a key species for global warming.
The rates of increase of pollutant concentrations in the cities of developing countries are higher than those of developed countries (Kato et al., 1991). Dhaka, the capital of Bangladesh, having a population of about 9 million is one of the biggest cities of the developing countries. It is expanding very rapidly due to high influx of people from rural areas. Emissions from various kinds of diesel traffic vehicle and badly maintained automobiles contribute most to air pollution problems. As brick is the main material for building construction in Dhaka, a lot of brick fields (which use coal as main fuel and operate only in winter due to meteorological condition) have grown up around Dhaka, especially in the northwest and southeast side of the city. These brick fields are another major contributors to the severe air pollution in winter in Dhaka. The adverse meteorological conditions in winter further aggravate the situation. But no systematic measurements of air pollution in Dhaka have been done until now due to limited measuring facilities and economic constraints.
To develop a reliable control strategy it is necessary to know the present pollution levels. Diffusion tube samplers were used for monitoring SO2 and NO2 concentrations in Dhaka. The samplers require no maintenance or power supply since they collect SO2/NO2 via molecular diffusion. This method has been extensively used for measurements of ambient SO2/NO2 concentrations in both urban and rural areas (Atkins et al., 1986; Bower et al., 1991; Gair et al., 1991; Maeda et al., 1994).
The development of efficient control strategies for air pollution problem in urban area should also be based on a better understanding of the physical and chemical processes that govern the formation, transport, diffusion, chemical transformation and removal of the pollutants. A mathematical model incorporates the necessary analytic framework for describing the physics and chemistry of polluted urban airsheds and simulating urban air pollution episodes. So that, the mathematical model has been extensively used to calculate the distribution of air pollutants and to formulate effective strategies for controlling the air pollution (Juda, 1986; Pilinis et al., 1993; Kumar and Russell, 1996).
In this study, we have measured the concentrations of SO2 and NO2 in Dhaka city on a large scale using diffusion tube samplers, derived their spatial distributions, and compiled emission source inventories over Dhaka. The paper also reports the application of an Eulerian transport/chemistry/deposition model (Kitada et al., 1984; Carmichael et al., 1986; Kitada et al., 1993) to simulate SO2 and NO2 concentrations over greater Dhaka. An investigation on the chemical conversion of SO2 to SO2-4, and NO2 to other nitrogen species over Dhaka is also performed. These are the first results of systematic measurements and modeling efforts in Dhaka. This study will give use-ful information for emission-control strategies and decision-making processes such as planning and management for preserving preferable atmospheric environment in the large cities of the developing countries like Dhaka.
Section snippets
The method
The molecular diffusion tube method, described in Maeda et al. (1994), was used to measure the concentration distributions of SO2 and NO2 in Dhaka city and its suburbs during the period from mid-December, 1995 to mid-January, 1996. The sampler, a plastic tube, 33 mm long and 36 mm in diameter, had a cap at one end. One piece of aluminium foil, polyethylene sheet, absorption medium (filter paper coated with reagent), and two pieces of polyflon filter paper were placed into the tube in the order,
Emission estimation
Emissions from various sources in Dhaka were estimated to understand their relative contributions to SO2 and NO2 concentrations. The anthropogenic emissions of SO2 and NOx in Dhaka in winter 1995–96 were computed using fuel consumption and emission factors for the unit consumption. Major sources of SO2 and NOx over Dhaka are listed in Table 1 with their emission factors and the total amounts. These emission data were compiled using published reports, journals, and personal communication with
Meteorology at the study area
Meteorologically, the year of Bangladesh can be divided into four distinct seasons; pre-monsoon (March– May), monsoon (June–September), post-monsoon (October–November) and winter (December–February). A brief summary of the average meteorological conditions (1991–1995) in Dhaka for different seasons is given in Table 3. From Table 3, the winter is characterized by 13–27°C average temperature. During these winter months, wind blows very weakly from northwest direction with an average speed of 0.8 m
Analysis of the concentration distributions of SO2 and NO2 over Dhaka
Fig. 4a shows the spatial distribution of the measured 10-day-average SO2 concentration over December 1995/January 1996 period in Dhaka. In Fig. 4a extremely high SO2 can be found in the southeastern industrial and brick field zone, where the highest concentration is over 100 ppb. The polluted zone, in which the average SO2 was over 40 ppb, extended along the major road running from northwest to southeast, and also parallel to the Buriganga river in the Dhaka area. Formation of this polluted zone
Modeling description
A three-dimensional Eulerian photochemical model (Kitada et al., 1984; Carmichael et al., 1986; Kitada et al., 1993) that accounts for the transport, chemical conversion and removal of pollutant was used to simulate SO2 and NO2 concentration distributions over Dhaka. The chemical mechanism used in this model is adapted from the work of Lurmann et al. (1986), the mechanism which includes 148 reactions among 68 species; the modified chemical mechanism is based on the condensed model by Lurmann et
Conclusions
Ambient SO2 and NO2 concentrations have been measured in Dhaka city in winter at 64 sites using diffusion tube samplers. Emissions of SO2 and NOx have been estimated and their relations to the SO2 and NO2 concentration distributions over Dhaka have been analysed, together with meteorological conditions. An Eulerian transport/chemistry/deposition model has also been used to estimate SO2 and NO2 concentrations, and their conversion rates to other species in Dhaka in winter. The model predictions
Acknowledgements
The authors acknowledge Mr H. Mori at Techno Chubu Co. Ltd and Prof. Y. Kiso at Toyohashi University of Technology, Japan for providing laboratory facilities and invaluable assistance with the chemical analysis. We also acknowledge the help of Drs M. Gamo and S. Yamamoto at National Institute for Resources and Envir-onment, Japan for providing us aerological data of Dhaka and valuable information on atmospheric diffusion in eastern India. Profound thanks are also due to Profs S. Ohta and N.
References (34)
- Ahmad, J. U., Carmichael, G. R., Ullah, S. S. and Haque, R. (1996) The increased concentration of SO2 and threat to the...
Model predictions of the rates of homogeneous oxidation of sulfur dioxide to sulfate in the troposphere
Atmospheric Environment
(1979)- et al.
Sulfur dioxide emissions and sectorial contributions to sulfur deposition in Asia
Atmospheric Environment
(1997) - et al.
The measurement of nitrogendioxide in the outdoor environment using passive diffusion tube samplers
(1986) Urbanization of developing countries and its influence on the environment
Environmental Information Science
(1995)- et al.
A diffusion tube survey of NO2 levels in urban areas of the UK
Atmospheric Environment
(1991) - et al.
Observed regional distribution of sulfur dioxide in Asia
Water, Air and Soil Pollution
(1995) - et al.
A second generation model for regional-scale transport/chemistry/deposition
Atmospheric Environment
(1986) - EPA (1985) Compilation of Air Pollutants Emission Factors, 4th Edn, Vol. 1. Research Triangle Park,...
Development of a simple passive technique for the determination of nitrogen dioxide in remote continental locations
Atmospheric Environment
Mixed-layer characteristics as related to the monsoon climate of New Delhi, India
Boundary-Layer Meteorology
Modelling of the air pollution in the Cracow area
Atmospheric Environment
Anthropogenic emissions of SO2 and NOx in Asiaemission inventories
Atmospheric Environment
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