关键词：大气；温室气体；环境保护
摘 要：Anthropogenic sources of air pollution emissions include a number of sectors and activities e.g., fossil fuel and biofuel combustion in industrial and residential areas, transportation (road, rail, air and ships), waste disposal, industrial processes, agricultural activities, solvent production and usage. Emissions of greenhouse gases (GHGs), such as Carbon dioxide (CO_2), methane (CH_4) and nitrous oxide (N_2O) are a major concern from climate change perspective. This because they obstruct the escape of infrared (heat) energy to outer space by absorbing them and leading to increase in earth's temperature along with other climatic changes (Bond et al. 2004). Anthropogenic activities annually attribute to an estimated 3%, 64%, and 24% of global emissions of CO_2, CH4 and N_2O, respectively (Duxbury 1994). Megacities contribute a major portion in these global emissions. As reported by Butler et al. (2008) megacities account for approximately between 9% and 12% of the global emissions of CO, NO_X, and NMVOC.