Seasonal and interannual variability in absorbing aerosols over India derived from TOMS: Relationship to regional meteorology and emissions

Abstract

The objective of this study is an analysis of the spatial, seasonal and interannual variability of regional-scale aerosol load over India, detected by TOMS during 1981–2000, with an evaluation of potential contributing factors, including estimated anthropogenic aerosol emission trends and regional meteorology (rainfall and circulation patterns). Spatial distributions in TOMS Ai were related to the emission densities of anthropogenic absorbing aerosols in April–May, but varied seasonally and were modified significantly by higher atmospheric dispersion in January–March and rainfall in June–September, both of which lead to low TOMS Ai, even in regions of high aerosol emissions. Dust emissions explain the high TOMS Ai over northwest region during April–May and June–September when rainfall is scanty and significant air-mass decent occurs in this region. The magnitude of TOMS Ai correlated with the anthropogenic absorbing aerosol (black carbon and inorganic matter) emission flux in five selected regions, dominated by biomass/biofuel burning and fossil fuel combustion, but not in a region with significant mineral dust emissions. The seasonal cycle in TOMS Ai was related to the seasonal variability in dust, biomass burning emissions and rainfall. Interannual variability in TOMS Ai was linked to that in forest burning emissions in the northeast, as evidenced by a correlation with ATSR fire-counts, both significantly enhanced in 1999. Trends in anthropogenic emissions during 1981–2000 potentially contribute to increases in the aerosol load detected by TOMS. This would need further investigation using analysis incorporating both trends in anthropogenic emissions and the interannual variability in natural sources of aerosols.