Variability of Atmospheric Aerosols Over India

Abstract

Atmospheric aerosols play a significant role in climate change due to their ability to scatter and absorb the incoming and outgoing radiation (direct effect). In addition to this, aerosols can also impact climate through modifying cloud properties, such as droplet size distribution and cloud lifetime, a process known as “indirect effect.” Recent studies using long-term data on aerosols (>25 years in some locations) obtained from the ARFINET have revealed a statistically significant seasonally dependent increasing trend. Comparison with measurements taken about 50 years ago indicates the phenomenal nature of the increase in aerosol loading. The rate of increase is high during December to March (dry months) over the entire region. However, the trends are incoherent during April to May (pre-monsoon) and June to September (summer monsoon period). The characteristic features of the spectral variation in aerosol optical depth (AOD) clearly demonstrate the impact of anthropogenic activities on the increasing trend in aerosol loading. Data from a remote coastal location in the southern peninsula (Thiruvananthapuram), on the concentration of BC, normally considered as a tracer for human impact, show a decreasing trend of ~250 ng m−3 per year. This is particularly perceptible after 2004. CAIPEEX data reveal that during the monsoon season, aerosol number concentration showed strong vertical gradient with a transition between the boundary layer and free troposphere.