Characteristics, seasonality and sources of carbonaceous and ionic components in the tropical aerosols from Indian region

To better characterize the tropical aerosols in Indian region, PM10 samples collected from Chennai, India (13.04 degrees N; 80.17 degrees E) were analyzed for carbonaceous and water-soluble ionic components. Concentration ranges of elemental carbon (EC) and organic carbon (OC) were 2.4-14 mu g m(-3) (ave. 6.5 mu g m(-3)) and 3.2-15.6 mu g m(-3) (ave. 9.1 mu g m(-3)) in winter samples whereas they were 1.1-2.5 mu g m(-3) (ave. 1.6 mu g m(-3)) and 4.1-17.6 mu g m(-3) (ave. 9.7 mu g m(-3)) in summer samples, respectively. Concentration of secondary organic carbon (SOC) retrieved from EC-tracer method was 4.6 +/- 2.8 mu g m(-3) in winter and 4.3 +/- 2.8 mu g m(-3) in summer. OC accounted for 38.5 +/- 14 % (n = 49) of combined concentrations of carbonaceous and ionic components in PM10. We also found that OC concentrations are generally higher than those of SO42- (8.8 +/- 2.5 mu g m(-3) and 4.1 +/- 2.7 mu g m(-3) in winter and summer, respectively), which was the most abundant ionic species (57 %) followed by NH4+ (15 %) > NO3- > Cl- > K+ > Na+ > Ca2+ > MSA(-) > Mg2+. The mass fractions of EC, organic matter (OM) and ionic species varied seasonally, following the air mass trajectories and corresponding source strength. Based on mass concentration ratios of selected components and relations of EC and OC to marker species, we found that biofuel/biomass burning is a major source of atmospheric aerosols in South and Southeast Asia. The high concentrations of SOC and WSOC/OC ratios (ave. 0.45; n = 49) as well as good correlations between SOC and WSOC suggest that the secondary production of organic aerosols during long-range atmospheric transport is also significant in this region. This study provides the baseline data of carbonaceous aerosols for southern part of the Indian subcontinent.