Aerosol optical depth trends over different regions of India

Seasonal and annual mean trends in aerosol optical depths (AODs) for the last decade are derived using MODerate resolution Imaging Spectroradiometer (MODIS) Level 2 10 km × 10 km remote sensing data over different locations in India. AODs have increased across India in the last decade. AOD trends exhibit spatial, seasonal and annual mean variations. Annual mean AODs have increased by >40% during 2000–2009 in Jaipur, Hyderabad and Bengaluru. The increase in AODs over Hyderabad and Bengaluru, major high-tech cities, can be ascribed to the increase in urbanization. An increase in AODs over New Delhi where manmade aerosols are dominant can be attributed to an increase in the amount of aerosols from fossil fuel and biomass burning, while an increasing trend in AODs in the northeast, indicates an increase in the amount of aerosols produced from biomass burning and forest fires. AODs decreased in the high altitude sites of Shimla and Dehradun. AODs and wind speeds increased over Jaipur, while they decreased in Trivandrum during the last decade. An increase in wind speeds led to an increase in soil derived dust particles over Jaipur, an arid site, while a decrease in wind speeds over Trivandrum, contributed to a decrease in sea spray aerosols thereby causing a decrease in AOD. Annual rainfall increased by ≤1% in most locations. Both AODs and rainfall have increased in the last decade over most study locations. These findings become important and useful in the context of regional and global climate change due to aerosols.

► Aerosol optical depths increased across India in the last decade.
► AOD trends exhibit spatial and seasonal differences.
► AODs increased over most urban areas.
► AODs increased over northeast India dominated by natural sources.
► AODs decreased over high altitude sites.