Carbonaceous and water-soluble inorganic aerosols over a semi-arid location in north west India: Seasonal variations and source characteristics

This paper presents the seasonal features of major carbonaceous components in aerosols, their source characteristics and the role of meteorology in influencing the chemical characteristics of aerosols at a semi-arid location Udaipur (24.5°N; 73.6°E), India, based on the analysis of PM10 samples (N = 128) collected during 2010–14. The samples were analysed for OC (organic carbon), EC (elemental carbon), CC (carbonate carbon), WSOC (water-soluble OC), WSTN (water-soluble total nitrogen) and water-soluble inorganic ions. Primary and secondary OC (POC and SOC), water-insoluble OC (WIOC) and water-soluble organic nitrogen (WSON) were also estimated. The carbonaceous aerosols (TC) contributed to ~23% of PM10 loading. Both EC and OC mass loading showed high values during dry period (October to May) (OC = 26 ± 14 μg m−3, EC = 3.2 ± 2.2 μg m−3 with the PM10 mass loading of 140 ± 52 μg m−3) compared to wet period (June to September) (OC = 16 ± 10 μg m−3, EC = 1.4 ± 0.8 μg m−3 with the PM10 mass loading of 84 ± 43 μg m−3). While the crustal species, biomass tracers and anthropogenic species dominated during dry period, the sea salt species (Na+, Cl−, ss-SO4, ss-Mg, ss-Ca, ss-K) were comparatively higher in wet period. OC was found to be predominantly water-insoluble and secondary in nature. Local anthropogenic/natural emissions and marine transported aerosols (by south-westerlies) contributed during wet period, while dry period is influenced by transported anthropogenic aerosols from IGP and northern India (by north/north-easterlies) along with mineral aerosols from desert regions (by westerlies). Monthly average contribution of total carbonaceous aerosols (TCA = OM (organic matter) +EC + CC) varied from 20 to 42%, over a year while the water-soluble ionic fraction varied from 16 to 36% of the PM10 mass. The un-analysed part which is mostly mineral dust contributed 39–55%.