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IN PAKISTAN, the atmosphere is being polluted by different sectors i.e. industry, power plants, automobiles, fertilizers, and petroleum refineries. These sectors contributing highest amount of pollutant smoke in the atmosphere. The northeastern side of Pakistani border is also fueled by neighbouring areas of India such as Amritsar, Chandigarh, Bathinda, and Nangal. In the winter season, satellite images show a dense fog in this region, which is directly related to meteorological conditions but it become dense and for the longer duration due to concentrated particulate matter called Black Carbon (BC).
Black carbon is consists of strongest light absorbing particulate matter. Due to incomplete combustion of fossil fuels, it can absorb a million times more solar energy than carbon dioxide. The major part of Black Carbon is composed of “soot”, which is a mass of impure carbon particles resulting from the incomplete combustion of hydrocarbons and also contains some organic carbon.
With the increasing urbanization in Pakistan, the air quality of cities is deteriorating and is becoming a serious challenge and causing damage to human health and the environment. The air quality of Pakistani urban cities is being polluted from different sectors, such as power plants, industry, automobiles, petroleum refineries, and fertilizer plants.
According to 2014 Environment Performance Index (EPI), which tracked national environmental performance on a quantitative basis for 178 countries, Pakistan is ranked at 148. And, according to the same index in 2012, Pakistan was ranked at 120 out of 132 countries; hence the improvement in this regard is almost zero. The most tragic situation is in Air Quality Issue of this index, where Pakistan ranked at 175 out of 178 countries listing, according to 2014.
BC contributes to the adverse impacts on human health, ecosystems, and visibility associated with ambient fine particles (PM2.5). Short-term and long-term exposures to PM2.5 are associated with a broad range of human health impacts, including respiratory and cardiovascular effects as well as premature death.
It is estimated that about 7 million premature deaths annually linked to air pollution, WHO report 2012. According to the same report, low and middle income developing countries of South-East Asia and Western Pacific Regions are contributing 3.3 million deaths (particularly women and children) due to indoor air pollution and 2.6 million deaths due to outdoor air pollution, which is about 82.85 percent of the total death toll. This means that by reducing black carbon in the atmosphere can reduce the risk of 7 million premature deaths annually.
At one side, Black Carbon pollutes the air quality, but at the same time it influences climate by directly absorbing light; reducing the reflectivity (“albedo”) of snow and ice through deposition, and interacting with clouds. The resulting increase in temperatures and accelerated melting of snow and ice. Black Carbon also causing a variety of damaging environmental effects on human, agriculture, and plant and animals ecosystem. The most sensitive regions like Himalaya and Arctic are predominantly vulnerable to these effects of BC.
The Black Carbon particulate matter contains carcinogens; therefore it is harmful to humans. Humans are exposed to BC by inhalation of air; candles and biomass, and traffic and industrial gases waste are major sources of indoor and outdoor exposures. It is observed that high concentrations of black carbon are recorded during driving in rush hours, on populated highways, and in traffic jams.
The life of black carbon in the atmosphere is about a week which is quite lesser than the carbon dioxide which lasts centuries. Hence, the spatial distribution of BC aerosols is extremely uneven.
Due to the short life of black carbon, it is comparatively easy to control it in the atmosphere. There are three common ways to remove it from atmosphere i.e. dry, wet, and gravitational deposition, in which the most important is rainwater washing and cleaning (wet deposition).