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Characteristics of Air Pollution Condition in Dhaka City- Effect of Automobiles and Factories on Environment

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PRABAL KANTI ROY* , Seiji HAYAKAWA**

(* United Department of Agricultural Science , Graduate School of Tottori University, Tottori 680, JAPAN)

(** Faculty of Agriculture, Yamaguchi University ,Yoshida, Yamaguchi 753, JAPAN)

 

ABSTRACT

This paper attempts to make clear the characteristics of the magnitude and scope of automotive and factory pollutant emissions in Dhaka city - which are creating an environmental problem in the city. About 451 factories in this city discharge and dump hazardous waste with no regard for the resulting surface and ground water or airpollution. Most of these factories are bereft of adequate emission treatment. In addition, the increasing traffic, inadequate urban transport infrastructure and services, and an aging and obsolete motor vehicle fleet are giving rise to high air pollution levels. About 86% of the total motor vehicles in this city emit black smoke above the International Standard of 65 HSU. Changing meteorological conditions, such as average wind velocities , wind direction and frequency of showers have influenced the pollutant concentration in the city's air . Without effective measures to control pollutant emissions, the city dwellers will be exposed to unhealthy and dangerous levels of air pollution from automobiles and factories.

 

Key words : Air pollution, traffic congestion, motor vehicles, HSU, meteorological condition.

 

1. Introduction

 

The motor vehicle usage has increased tremendously in Dhaka, and like other metropolitan cities, Dhaka is also facing a pollution problem from emissions of carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides(NOx), and particulate matter (PM). Besides this, about 451 polluting industrial plants such as tanneries, textile mills, oil refineries, distilleries, fertilizers, paint manufacture, pulp and paper factory etc. discharge highly toxic effluent directly into the river in Dhaka. In a thickly populated area like Hazaribagh, there are about 160 tanneries discharging 28 to 35 litres of waste effluent for each kilogram of hide processed which contains toxic heavy metals like chromium, arsenic, zinc etc. These run through open drains and fill the whole area with a putrid smell. About 1.3 million people in Dhaka depend on 6 x10 metric ton of wood and other non-conventional fuel in each year, which causes thick smoke from their cooking stoves. The purpose of this paper is to briefly survey the air pollution conditions in Dhaka city.

 

2. Meterial and Method

 

Dhaka, the capital of Bangladesh has an area of 425 square kilometers and a population of about 6 million. The topography of Dhaka is flat and slightly above sea level. The area belongs to the tropical region and has three dominating seasons. Winter (Nov. -Feb.), Summer (March - June) and Monsoon (July - Oct. ), having average temperature 21 degree to 39 degree Celsius in summer and 11 to 29 degree celsius in winter and average rainfall is 1194 mm to 3454 mm annually and average humidity is 80 percent.

 

The conentrations of SPM, NOx and SOx were measured by using high volume sampler and spectrophotometer. The total emission was estimated on the basis of fuel consumption by the vehicles, amount of natural gas used in households, for commercial purposes and in industries and other non-conventional fuels used in the city.

 

Fig.l. Location of Dhaka city and the observation points.

 

3. Result and Discussion

3.1.Motor vehicles and urban air pollution

 

The total number of motor vehicles registered in 1988 was 270860 in the country which is not so high in comparison with the other developing countries, but, due to the higher emission percentage from the motor vehicles the city atmosphere becoming unhealthy for its people.

Table . Automobile exhaust in Dhaka city, May 1990 (Department of Environment, Govt. of Bangladesh).

 

 

In the city, road traffic accounts for as much as 57% to 92% of NOx and 17% to 95% of HC, and a major share of particulates. On highly congested streets , these levels can rise even further. The smoke and malodorous fumes emitted by diesel buses on busy congested streets are often perceived as more damaging to health by the public than the invisible emissions from automobiles (Faiz, 1993). Compared to the other cities, the magnitude of pollutant emissions in Dhaka city is seemed to be safe, but may have to be balanced against other environmental issues such as water quality, solid-waste disposal and indoor air pollution . From the data in Table 2 and Table 3 the generalized inferences can be drawn as'follows regarding the role of motor vehicles in urban air pollution :-

i. Motor vehicles are the primary source of CO emissions in urban areas -100% of the share , accounting for about80 .

ii. In Sao Paulo and in Dhaka, the motor vehicle share of SOx emissions is uncharacteristically high because of the extensive use of motor vehicles run on poor quality diesel fuel with a high sulphur content.

iii. Motor vehicles are a small contributor to suspended particulate matter(SPM) emissions .

 

The mixing of lubricating oil with fuel in order to reduce the fuel cost is a tendency observed among the auto-tempo drivers in Dhaka. It also results in unburned hydrocarbons especially higher levels of hydrocarbons and sulphur compounds emitted into the atmosphere which cause acute eye irritation of pedestrians and passengers .

 

3.3. Air quality in Dhaka

 

Among the observation points in Fig. 2 the Lalmatia area is closer to the northern highway, truck depots, tempo(3-wheel vehicles) and bus stands. Due to more diesel vehicles, bus and tempos plying in it's vicinity, even if total vehicular traffic is less than in the Motijheel area, theSPM and NOx concentration in Lalmatia is higher than in other areas. Also, the considerable construction activity going on in the Lalmatia area might contribute to the local SPM . In the SOx observation, it is seen that emissions in Tejgaon Industrial area have little or no influence on the SO 2 values which may be due to the partial SO2 data from this area.

 

Fig. 2. Seasonal changes of SPM, SOx and NOx.

 

In Lalmatia, probably the brick fields (using coal or wood as fuel ), and heating / burning of coal tar (bitumen) for the construction or repair of flexible pavements are a source of SO2.The Environment Department reported that the emission concentration and SPM in the air has lower value in the mid-year - which shows the influence of the changing meteorological conditions : (i) less periods of calm (ii) higher average wind velocities (iii) a sharp change in wind direction from the dominant WNW to SW and (iv) increasing frequency of showers (Fig.2). The SPM and NOx observation results indicate that probably immediate vertical and lateral dispersion from local pollutants is much more important than the transport over wider areas.

 

In Table 4, BUET is not situated at any busy traffic point, but some days the pollution concentration is high because of the wind direction and wind speed causes transfer of pollutants from the point of emission. The Hatkhola, Dainik Bangla and Press Club points are mainly traffic points. In addition, wind also transfers pollutants from the neighbouring factories. Farmgate is the big intersection of traffic points. Within the Tejgaon industrial area there are many factories. Pollution in this spot is so high that it can be recognized by strong turbidity, bad smell and eye irritation - caused by the combination of many high emitting vehicles, frequent traffic jams and chemical processing in the factories. It is seen that the SO2 emission in the Farmgate area has an impact on the environment. Thick deposits of unburnt hydrocarbon particles are observed over the buildings in this area and the traffic police working here report nausea and headaches while on duty. These may be caused by the pollutants and the emissions from the growing numbers of factories and motor vehicles in this area.

 

 

The epidemiological studies of air pollution are still inadequate. The number of complaints related to the health effects of air pollution are growing among the city dwellers. The Chest and Heart Bulletin Vol. X No. 2 July 1986 reported that 11.57% of the 13000 patients surveyed are affected by respiratory disorders in the two main city hospitals in Dhaka.

This study suggest that modifications of the existing vehicles , effectiveness of the environmental legislation and awareness of the people would reduce the pollution in Dhaka city.

 

References

A. Faiz,1993: Automotive emissions in developing countries and relative implications for global warming, acidification and urban air quality. Transp.Res., 27A, 3 ,167-186.

Anonymous,1991,Environmental Quality Standard (EQS), Department of Environment (DOE), Govt. of Bangladesh, 97-111.

G. Baumbach,1993,Air pollution caused by vehicular emissions in urban areas and near highways (germ.). Staub - Reinhaultung der Luft, 5 3 ,267 - 274.

S.Yousuf Shabriar; Md. Mahmud Hassan ,1993: Study of Air Quality Around Dhaka City. Unpublished Graduate Thesis , Dept. of Chemical Engineering, Bangladesh University of Engineering and Technology (BUET),Dhaka, Bangladesh,88 pp.

 

Source: jstage.jst.go.jp

 


 

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