Carbonaceous and Inorganic Aerosols over a Sub-urban Site in Peninsular India: Temporal Variability and Source Characteristics

Carbon in the atmospheric aerosols existing in the form of organic and elemental carbon has potential impact on climate, visibility and health. The major component of carbonaceous matter is organic carbon (OC) contributing up to 90% and a relatively lower contribution of 5-10 % from elemental carbon (EC). Characterisation and quantification of carbonaceous component of boundary layer aerosols (PM10) along with the water soluble inorganic ions at a suburban location in Coimbatore (10°53'53″N 76°54'01″E) in India was carried out. The results were analysed to identify the possible sources, to understand their seasonal variations and influence of local meteorology. The samples collected in campaign mode for one year (2014-15) for three different seasons (summer, winter, monsoon) were analysed for organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), water-soluble total nitrogen (WSTN) and inorganic ions, Na+, NH4+, Ca2+, Mg2+, Cl-, NO3-, SO42- and HCO3-, using standard analytical techniques. The primary (POC) and secondary (SOC) fractions of organic carbon were elucidated using EC tracer method. Majority of the measured chemical constituents showed maximum concentration during winter and minimum during monsoon. SO42- was the most abundant species in winter and summer while OC maximises in monsoon. OC and EC showed different diurnal patterns with OC peaking during daytime and EC during night-time. Primary OC contributed to 58% of OC fraction and 42% by secondary OC. SOC showed significant diurnal variability with daytime high which may be attributed to the increased photochemical activity during daytime. Average OC/EC ratio was 5.4 which showed less seasonal variability and a substantial diurnal variability. K+ showed good correlation with OC, EC, POC, WSOC, SO42-, and NO3- suggesting the possibility of biomass burning and fossil fuel combustion as the major sources of aerosols over the study region.