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Air Pollution by Fine Particulate Matter in Bangladesh

Bilkis A. Begum
Atomic Energy Centre, Dhaka (AECD), P.O. Box: 164, Dhaka, Bangladesh

Philip K. Hopke
Center for Air Resource Engineering & Science, NY, USA

Andreas Markwitz
Institute of Geological and Nuclear Sciences (IGNS), 30 Gracefield Road, Lower Hutt, NZ, USA

Abstract/ Executive Summary:

In Dhaka, Bangladesh, a particular matter (PM) is the air pollutant that is most harmful to public health and the environment when compared to other measured criteria pollutants. During recent years, the Government of Bangladesh has tried to control PM emissions coming from anthropogenic sources. About 30–50% of the PM10 mass in Dhaka (depending on location) is in fine particles with an aerodynamic diameter less than 2.2 µm. These particles are mainly of anthropogenic origin and predominately from transport-related sources. However, the combination of meteorological conditions, long-range transport during the winter and local sources results in PM concentrations remaining much higher than the Bangladesh National Ambient Air Quality Standard (BNAAQS). It has been found that black carbon accounted for about 50% of the total fine PM mass before the adoption of control policies. As a result, the PM emission, as well as BC, has not increased in proportion to the increase in the number of combustion sources like motor vehicles, diesel power generators or brick kiln. Positive Matrix Factorization (PMF) was applied to fine particle composition data from January 2007 to February 2009. It was found that motor vehicles contribute less BC with respect to brick kiln industry. This result demonstrates the effectiveness of the government’s policy interventions since previously vehicles represented the major contributors of BC. BC is also transported over long distances, mixing with other particles along the way as demonstrated by a potential source contribution function analysis. Transboundary transport of air pollution in the South Asian region has become an issue of increasing importance over the past several decades. The relative amounts of local and long-range transported pollutants are currently unknown.

Keywords: Particulate matter, Black carbon, Transboundary transport, Dhaka

Location: Dhaka, Bangladesh

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Pollution

Objectives:

The main objectives of this paper are to discuss the present status of particulate pollution in Dhaka, Bangladesh, its sources, and the likely locations of the sources of significant events of fine particles (PM_2.2) and BC concentrations over the region.

Methodology:

Sampling: BAEC sampling site. The Atomic Energy Centre, Dhaka (AECD) of BAEC operates a sampling site (semi-residential) for collecting PM samples using a “Gent” stacked filter sampler (Hopke et al., 1997) capable of collecting air particulate samples in coarse (2.2–10 µm) and fine (2.2 µm,) size fractions together. PM₁₀ concentration may be obtained by adding PM_2.2 and PM_10–2.2 concentrations. At the semi-residential area (SR) site, the sampler was placed on the flat roof of AECD campus building. The roof height was 5 m and the intake nozzle of the sampler was located 1.8 m above the roof. The intake was about 80 m away from the roadside. The sampler was placed so that the airflow around it was unobstructed. The airflow of the sampler was maintained at 17 L/m. This site began operation in December 1996. In this paper, the mass and BC concentrations data are presented through December 2011. The location of the sampling station in Dhaka. Samples were collected only on weekdays. There were generally no samples collected on Thursdays or Fridays. Samples were most commonly collected on Sunday and Wednesday. The samples were collected on Nuclepore filters with 8 µm pores for the coarse fraction samples and 0.4 ?m pores for the fine fraction samples. The diameter of the filter is 47 mm. The filters were equilibrated for 24 hours, weighed in an air-conditioned room (approximate temperature of 22 ºC and relative humidity of 50%) and stored in airtight petri slides. After sampling, the sample holder (NILU Stacked Filter Unit) was returned to the AECD Laboratory for recovery of the filters and the samples were equilibrated under the same conditions. The post–sampling weighing of the samples was usually completed within one month of the sampling date. A comparison of this sampler with an Airmetrics MiniVol sampler (Baldauf et al., 2001) showed that the Gent sampler provides comparable sampling efficiency (Begum and Biswas, 2005). Twenty-four-hour representative samples were collected twice a week in weekdays only. About 100 samples (each sample comprises one fine and one coarse) were collected every year from each of the sampling stations. The effective sampling time was varied between 6 and 20 h (depending on seasons) distributed uniformly over 24 h a day to avoid filter clogging and so that the flow rate remains within the prescribed limits of the sampler. This ensured proper size fractionation and collection efficiency. Intercomparison of GENT data with continuous 24 h Airmetrics MiniVol data by collocated sampling suggested (Begum and Biswas, 2005) that the data generated using such time-sliced sampling procedure provides reasonably accurate average PM mass data. PM mass and BC determination: The masses of the coarse and fine fraction samples were determined by weighing the filters before and after the exposure. A Po–210 (alpha emitter) electrostatic charge eliminator (STATICMASTER) was used to eliminate the static charge accumulated on the filters before each weighing. The concentration of black carbon (BC) in the fine fraction of the samples was determined by reflectance measurement using an EEL–type Smoke Stain Reflectometer. Secondary standards of known black carbon concentrations are used to calibrate the reflectometer (Biswas et al., 2003). Comparisons of the measured elemental carbon (EC) showed good agreement with the BC measurements for similar samples (Salako et al., 2012). Multi elemental analysis: Multi elemental analyses of the samples were made using proton-induced X-ray emission (PIXE) at the Institute of Geological and Nuclear Science (IGNS), New Zealand. The X–ray spectra obtained from PIXE measurements were analyzed using the computer code GUPIX (Maxwell et al., 1989; Maxwell et al., 1995). Concentration data for seventeen elements, and black carbon, were used for data analysis of the period of 2007 to 2009. The total number of samples were 166.

Source of Information: Atmospheric Pollution Research 4 (2013) 75?86

Article Link (Online Journal): doi: 10.5094/APR.2013.008

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The government of Bangladesh has been working to reduce the PM emissions by introducing lower sulfur fuel, improving the mobility of vehicles, and introducing new technology which is still under consideration for brick production. From this study, it is concluded that there is also a trailing effect of PM movement from the northwest towards the southeast that affects Bangladesh. This transport happens mainly during the wintertime when rainfall is minimal and wind speeds are low. However, it is not possible yet to quantify transboundary transport. As a result, the local air pollution effect is increased.

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