Carbonaceous aerosol over semi-arid region of western India: Heterogeneity in sources and characteristics

Carbonaceous species (elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC)) and water-soluble inorganic species (Na+, NH4+, K+, Ca2+, Mg2+, Cl-, NO3-, SO42-) in PM10 and PM2.5 from Ahmedabad and Jodhpur (urban and semi -urban locations, respectively) in western India were measured during May-September, 2011. Stable isotope composition of carbonaceous aerosol (delta C-13 of TC) in PM10 samples was also determined. Average EC concentration in PM10 at Ahmedabad was 1 mu g m(-3) (range: 034 to 3.4 mu g m(-3)), almost 80% of which remained in PM2.5. Similarly, 70% of EC in PM10 (average: 0.9 mu g m(-3)) resided in PM2.5 at Jodhpur. Average OC concentration at Ahmedabad was 6.4 mu g m(-3) and similar to 52% of this was found in PM2.5. On the contrary, OC concentration at Jodhpur was 40 mu g m(-3), 80% of which was found in coarse particles contributing substantially to aerosol mass. delta C-13 of TC (average: - 27.5%., range: -29.6 to 25.8%.) along with WSOC/EC ratio shows an increasing trend at Jodhpur suggesting the possibility of aging of aerosol, since aging results in enrichment of heavier isotope. OC and WSOC show significant correlations with K+ and not with EC, indicating biogenic origin of OC. Different size distributions are also exhibited by WSOC at the two stations. On the other hand, delta C-13 exhibits an inverse trend with sea -salt constituents atAhmedabad, indicating the influence of air masses transported from the western/south-western region on carbonaceous aerosol. These results suggest that a strong heterogeneity exists in the sources of carbonaceous aerosol over this region and potential sources of non-combustion emissions such as bio-aerosol that need further investigation. (C) 2016 Elsevier B.V. All rights reserved.