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Air Pollution Aspects of Dhaka City

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Ahmmed, K. M. Tanvir and Begum, D. A.

Dept. of Chemical Engineering, BUET, Bangladesh

 

Abstract—This study is focused on the measurement of air pollution levels at traffic congestion and brick field. Indoor air pollution levels near to different types of cooker and in dwelling rooms have also assessed. It has been revealed that pollution   level   at   traffic   congestions   has   considerably improved due to large scale introduction of CNG vehicles in Dhaka city. Indoor pollution level assessment data show that cooks of Dhaka city are exposed to high concentration of CO, NOx    and  SOx.    Some   recommendations   for   air  pollution control in Dhaka city are also incorporated in the paper.

 

INTRODUCTION

 

Air pollution can be defined as any atmospheric condition in which substances (natural   or   man-made chemical   compounds   capable of being airborne) are present at concentrations high enough above their normal ambient  level  to  produce  a  measurable  effect  on man, animals,   vegetation, or materials. Air pollutants are hazardous to human health and at high enough concentrations can even be fatal. The most important pollutants are Carbon monoxide  (CO), Sulfur  dioxide (SO2), Nitrogen oxides (NOx), Ozone (O3), Hydrocarbons (HC) and Suspended Particulate Matter (SPM). In the late 1970s, Environmental Protection Agency (EPA) of USA added  lead  (Pb)  to  this  list.  Particulate  matter  with  an aerodynamic diameter of less than or equal to 10µm (PM10) was added to the list in 1987.

 

Air pollution can cause drowsiness, eye irritation, throat irritation, persistent cough, asthma, nose   blockage, respiratory infections, bronchial infections, colds and headaches  in  human  being.  Lead  in  air  can  affect  the central nervous system, cause renal damage and hypertension. CO in air  reduces the ability of blood  to carry oxygen and exacerbates heart disorders.

 

Dhaka, one of the mega cities of the world, witnessed a very fast growth of urban population in recent times. Air pollution  in  Dhaka  city  is  reported  to  be  serious  and damaging to public health. In the winter of 1996-97, air pollution of Dhaka city became the severest when lead in the air was reported higher than in the atmosphere of any other place of the world [1]. Concern over air pollution rate of  Dhaka  city  ultimately  led  to  the  promulgation  of National Ambient Air Quality Standards in Bangladesh in 1997.

 

A  study  of  impact  of  auto-exhaust  on  air  quality  of Dhaka  city  has  been  conducted  in  the  year  2000,  it  is revealed that traffic congestion, fuel quality and brick field emission  are  the main  reasons  of  air  pollution  in  Dhaka city [2]. To control air pollution level CNG at large scale has  introduced  in  Dhaka  city.  Air  quality  of  Dhaka  city after  large  scale  introduction  of  CNG  vehicles  has  been studied in this investigation.

 

As  people  spend  most  of  their  time  indoors  and  the concentrations of pollutants may build up in an enclosed space, the risk to health may be greater to exposure to air pollution indoor than outdoor. For the first time, indoor air pollution  level  of  Dhaka  city  has  also  been  assessed systematically during this study. Brick field emission level data  have  also  presented.  In  this  paper  the  results  of investigation  on  air  quality  of  Dhaka  city  have  been assessed and put forward some recommendations.

 

EXPERIMENTAL

In this investigation Gastec technique (Japanese origin) is   used   for   CO,   CO2,   NOx     and   SO2     concentration determination.   High   Volume   Air   Sampler   (Graseby Andersen) is used for PM10  concentration determination. Experiments   are   conducted   in   accordance   with   the procedure  recommended  by  the  manufacturers  of  the equipment.

 

RESULTS AND DISCUSSIONS

 

The ambient air quality of Dhaka city with respect to CO, SO2, NOx, CO2 and PM10 is summarized in Table I.

 

 

A comparison between previous data and data obtained during   this study has been presented in Fig. 1, Fig. 2, Fig.3 and Table II. The standard limits of air pollutants set by the Department of Environment (DoE) of the Government of  Bangladesh  (GoB)  are  included  in  Table  I.  From  the experimental values, it is apparent that in terms of PM10 the situation  is  alarming.  The  experiments  are  conducted during the period of 4pm to 8pm. It is selected because the previous work done by D. A. Begum [2] shows that the pollution level is high in Dhaka city during that period.

 

The  concentration  level  of  CO  is  within  the  limit  of Bangladesh Standards [ECR,2005].       But the concentrations of NOx in  the  ambient  air  exceed  the standard  values  set  by  the  Department  of  Environment, GoB. But, it may be mentioned here that the standard value of NOx  set by the DoE is annual average and the results shown in Table 1 are 4 hours average.

 

 

 

It is observed from Fig. 1 that, CO concentrations are decreased after CNG introduction and banning 2-strokes 3-wheelers. Fig. 2  shows the comparison of NOx concentrations before and after    large-scale CNG introduction. The level of NOx has decreased significantly. Only at Mohakhali it is slightly increased because the NOx concentration  at  Mohakhali  was  previously  measured  at different time than this study.

 

 

The concentration of suspended particulate matter in the ambient  air  varies  greatly  with  weather conditions.  It  is observed  form  Fig.3  that  the  values  have  decreased  in recent times. But it is still far from the Amended Standard of Bangladesh (150 µg/m3). It is assumed that decreasing tendency of particulate matter emission is related to large-scale CNG-run vehicles.

 

Indoor  Air  pollution  has  not  been  studied  much  in Bangladesh. Under the supervision of D. A. Begum a study has carried out on indoor air pollution of Dhaka city [5]. This study has emphasized on different types of fuel used in   household   of   Dhaka   city.   Suspended   particulate materials are not measured in these studies. Only CO, NOx and SO2  emission levels are measured

 

 

First eight of the fuels presented in Table III are burned in   the   same   earthen   cooker   (matir   chula).   And   the concentration of the pollutants is measured at the breathing level of a cook. So, it represents the real exposure of a cook to the pollutants. Table III indicates that, higher level of CO concentrations is recorded for leaf, charcoal and straw. Maximum  SO2 emission  is  recorded  for charcoal  and bamboo.  NOx  level  for  straw  is  highest.   As  a  result  of exposure  to  smoke  to  these  dirty  cooking  fuels  many children and woman are getting sick. Slum dwellers using the first eight types of fuels listed in Table III are severely affected. But those who use kerosene and natural gas as a fuel are affected less.

 

 

From the experimental values of Table IV, it is apparent that  indoor  pollution  levels  at  places  other  than  kitchen (with respect to CO, SO2  and NOx) in Dhaka city is not an immediate concern for health.

Numerous brick making kiln operating in the dry season are one of the major sources of air pollution in Dhaka city. From Table V, it has been noticed that the concentration of SPM  is  higher  than  the  Bangladesh  standard  value  for SPM (400µg/m3) and other pollutants level are within the limit.

 

 

CONCLUSION

The air quality has improved after large-scale launching of CNG driven vehicles, introducing lead free petrol and banning  2-strokes  3-wheelers.  This  recently  assessed  air quality of Dhaka city has revealed that more actions should be undertaken to improve the air quality.

 

RECOMMENDATIONS

Vehicular  emission  can  be  reduced  by  replacing  old, worn-out  vehicles.  It  can  also  be  done  by  appropriate engine design, control strategies and maintenance services. The engines of the existing petroleum fuel based vehicles are  to  be  modified  so  that  they  can  use  CNG.  Catalytic converter, efficient filters and adsorbers can be used for vehicular  exhaust  gas  treatment  for  new  model  vehicles having appropriate control systems.

Eastern Refinery Limited (ERL) is about 50 years old now.  It  has  to  do  the  necessary revamping. Catalytic reforming and hydrofining processes are to be installed in ERL  so  that  it  can  produce  unleaded  gasoline  and  low sulfur  diesel. The  proposed  new  refinery  may  be  so designed that it produces low sulfur diesel and unleaded petrol.

Appropriate transportation planning is to be adopted to introduce  efficient  mass  transit. Rickshaws  are  to  be gradually phased out from the main roads. They may be allowed to operate in lanes and by-lanes only. The reason behind this is that they slow down the traffic, thus causing higher pollution.  Better  traffic  control  and  management with  flyovers, one-way streets, multistoried  parking, metered  parking  etc.  are  to  be  introduced.  Past  studies show that traffic congestion is the main reason behind high level of pollutants concentration at roadside of Dhaka city[7]. Railway  around  Dhaka city, flyovers, elevated highways, underground railways  if they are found to be cost-effective, are to be constructed to avoid traffic congestion.

 

Efficient  solid  waste  management  system  should  be introduced.  Door  to  door  household  waste  collection, collection of medical wastes from the hospitals and sorting out at sources of different wastes should be done.   Solid waste is to be centrally processed to valuable products.

 

For reduction of brick field emission level, stack heights should be increased. New  and  improved  technologies  of brick-making   should   be   introduced.   Low   sulfur   coal should be used in brickfields instead of high sulfur coal. Proper ventilation of kitchen, efficient cooking devices as well as quality fuel, can reduce the indoor air pollution. DoE and Bangladesh Road Transport Authority (BRTA) should enforce their regulations strictly. Government   has   to   ensure   effectiveness of   control programs through ambient air quality  monitoring. Coordination  between  DESA,  DWASA  and  BTTB  is needed to reduce the concentration of  suspended particulate matter in the air of   Dhaka city. Social awareness   about   the consequences of environmental degradation is to be created through mass media such as TV, radio and newspaper.

 

ACKNOWLEDGEMENT

We acknowledge the help and assistance of chemical engineering department, Bangladesh University of Engineering and Technology (BUET).

 

REFERENCES

[1]    N. Ahmed, “Air Pollution in Dhaka City,” Key note speech at ChE Division of IEB, May, 1997.

[2]    D.  A.  Begum,  “Air  pollution:  A  Case  Study  of  Dhaka  City”, presented at the conference “BAQ-2004”, Organized by Society of Indian Automobile Manufacturers, Agra, India, December, 2004.

[3]    M.  K.  Paul,  “A  Study  of  Continuous  Profile  of  Specific  Urban Pollutants,”  M.Sc.Thesis,  Bangladesh  University  of  Engineering and Technology, Feb. 2002, p. 95.

[4]    Md. W. Uddin and Md. M. Hasan, “Study of Particulate Matters in Air Around Dhaka City with  High  Volume PM10  and  APM 415 Samplers,”     B.Sc.Engg.     Thesis,     Bangladesh     University    of Engineering and Technology, Mar. 2002, p. 124.

[5]    M. A. Zaman and Md. M. Rahman, “Impact of Indoor Air Pollution on   Health,”   B.Sc.   Engg.   Thesis,   Bangladesh   University   of Engineering and Technology, Mar. 2009, pp. 32-34.

[6]    S.   Ahmed   and   I.   Hossain,   “Applicability   of   Air   Pollution Monitoring  in  a  Cluster  of  brickfield  in  bangladesh,”  Chemical Engineering Research Buletin, vol. 12, 2008, p. 32.

[7]    A. Faiz, C. S. Weaver and M. P. Walsh, “Air Pollution from Motor Vehicles, Standards and Technologies for Controlling Emissions,”Working Paper, World Bank, U.S.A., 1996.

 

Source: benjapan.org

 


 

 

 

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