Air in Dhaka is among the most polluted compared with that in other megacities of the world and the air quality becomes the worst in winter exposing the health of about 15 million people to risk, environment ministry official, quoting a recent study, said.
The World Health Organisation estimates that up to 10,000 premature deaths a year in Bangladesh are attributed to air pollution.
Concentration of sulphur dioxide (SO2) and nitrogen dioxide (SO2) was found far exceeding the permissible air quality grade set by the World Health Organisation and much higher than that in world’s other places such as Cairo, Ho Chi Minh City and Dakar where similar screening studies were conducted, the officials added.
The percentage of deadly ozone in Dhaka is, however, lower than that in Ho Chi Minh City, said the air pollution study conducted by Bangladesh’s Department of Environment and the Norwegian Institute for Air Research (Norsk institutt for luftforskning – NILU) in connection with the Clean Air and Sustainability Project.
The screening study conducted in Dhaka in January 31–February 15, 2011 was mainly aimed at gaining an overview of the background concentrations and the spatial distribution of the air pollution in the Dhaka area.
In addition, the study examined satellite mapping data to get a general regional picture of nitrogen dioxide and particulate matter concentrations and found that spatial patterns of nitrogen dioxide over Bangladesh exhibit a distinct hotspot over Dhaka.
The study also found that the annual average tropospheric nitrogen dioxide levels of Dhaka increased by approximately 75 per cent between 2003 and 2010.
A combination of numerous local emissions sources in winter in addition to special local and regional winter meteorological conditions gives the city exceedingly high air pollution concentrations.
Geographical distribution of sulphur dioxide results show that concentrations are the highest along the River Buriganga and surrounding areas, which is where much of the smaller industrial type operations as well as the some of the larger brick kiln fields are located.
The typical average sulphur dioxide concentrations measured in Dhaka was on an average higher than that in other cities such as Cairo and Ho Chi Minh City, the study said.
The ozone values were, however, found relatively low and the average ozone concentrations in Dhaka are also slightly less than those found in Ho Chi Minh City.
Particulate matter in the air was extremely high throughout the city exceeding any national and international permissible limit, the study of the DoE and NILU said.
Particulate matter with diameters less than 10µm can penetrate deep into the lungs and have adverse effects on the respiratory and cardiovascular systems, physicians said.
The air pollution situation was particularly grave in winter as a large portion of the particulate matter concentrations was due to regional haze and a large-scale cloud of dust covering a large portion of the northern Indian continent.
This can be due to the regional topography and meteorology which allows cold air from the Himalayas to flow down into north-eastern India, creating a super strong inversion layer which traps all pollution in this vicinity, the study report said.
Then the typical winds blow first eastward along the mountains and then towards the south over Bangladesh and transport the pollution with them, it added.
Local sources to these values include the numerous brick kiln fields numbering about 983 around Dhaka and the re-suspension of dust is a very much localised issue as well, officials said.
During winter, the brick kilns are the primary local source of air pollution specifically the particulate matter as most of them use ‘dirty’ coal from India as their primary fuel source, the report added.
The screening study was conducted in winter because of the dry period where air quality concentrations are at their peak and it is also time when all brick kilns, suspected to be the single greatest local contribution to air quality problems in Dhaka, are operational.
Other possible sources of air pollution cited in the study include re-suspension of road dust from traffic, open burning, and industrial sources such as cement manufacturing and metal smelting.
-With New Age input
