Size-segregated characteristics of carbonaceous aerosols over the northwestern Indo-Gangetic plain: Year round temporal behavior

Abstract

Size-segregated aerosol samples (PM<0.95, PM0.95–1.5, PM1.5–3.0, PM3.0–7.2 and PM>7.2) were collected over Patiala (30.33°N, 76.40°E; 250 m amsl), a semi-urban city located in northwestern Indo-Gangetic Plain (IGP) during October, 2012 to September, 2013. These samples were analyzed for carbonaceous aerosols (organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC)) to study their temporal variation, prevailing emission source (s) and secondary formation processes. Annual average of total suspended particulates (TSP) concentration, estimated by adding the aerosol concentrations in different size ranges, was found to be 199 ± 82 μg m–3, varying from 88–387 μg m–3 with majority of particulate mass found in submicron size (PM<0.95). OC3.0 and WSOC3.0 ranged from 5.4 to 70 μg m–3 (23 ± 14 μg m–3) and 2.5 to 37 μg m–3 (12 ± 8.7 μg m–3), respectively over an annual cycle. Highest mass fraction of OC (> 75%) and WSOC (> 80%) was observed in submicron size, suggesting that OC mainly comes from combustion and/or secondary source (s). It has been observed that almost half of OC is secondary. On the other hand, climate forcing agent EC in PM<0.95 varied from 1.1 to 9.8 μg m–3 (4.8 ± 2.2 μg m–3). High mass ratios of OC/EC (~1.5–7.2) and WSOC/OC (~0.33–0.68) indicate the relative dominance of biomass burning emission over the study region. Total carbonaceous aerosols account for ~10–59% of submicron particulates mass (PM<0.95), indicating that fine particulates are enriched with carbonaceous species. These results have implications to regional climate model development and validation.