Atmospheric Carbonaceous Matter over South Asian Region: A Review of Variation in its Thermal, Optical and Molecular Properties During Last Two-Decades

Abstract

Linear growth of atmospheric particulate matter (PM) over south Asia is one of the significant problems affecting human health and climate change. In addition, these particulate matters have the potential to absorb and scatter solar radiation, causing a disturbance in the earth radiation budget resulting in this region facing several floods and droughts, excessive glacier melting, loss of a million lives, and many more in the last two decades. This context aim to provide a brief knowledge of PM2.5 chemical composition and their optical properties. To assess, existing field studies conducted after the year 2000 were reviewed and summarized in terms of geographical, temporal and seasonal variation across the region. It is seen that PM2.5 were significantly increased by 25.04% in the last two decades. Annual PM2.5 was up to 10 times the prescribed limit set by world health organization (WHO) guidelines. Annual PM2.5 was higher in the northern than southern cities, and more increased in Indo-Gangetic plains (IGP) than coastal and southern region (CASR) and high altitude (HA) regions. The highest seasonal variation occurred in the winter months. Organic carbon and elemental carbon contribute nearly 31% of the annual average PM2.5 ranged from 14 to 70%. Higher variability in the percentage contribution of organic carbon and elemental carbon suggests different sources mainly influences this region. Biomass and fossil fuels, vehicular emission, and secondary aerosol are the major source factors in the inland region, while marine salt and soil dust are dominant fractions observed in a coastal area. Light absorbing brown carbon contributes significant amount in this region, and it’s clearly seen by aerosol optical depth, varied from 0.04 to 1 in the entire region.