Characterization of carbonaceous aerosols with special reference to episodic events at Agra, India

A continuous measurement of organic carbon (OC) and elemental carbon (EC) in PM2.5 and TSP was carried out at a suburban site of North central region of India. PM2.5 and TSP samples were collected from May 2010 to April 2011 and were analyzed for OC and EC using thermal optical transmittance (TOT) protocol. The results showed that the annual average concentrations of PM2.5 and TSP were 79.7 ± 40.5 and 247.5 ± 128.3 μg/m3, respectively. In PM2.5, OC and EC concentrations were 22.8 ± 17.1 and 3.4 ± 1.2 μg/m3 while in TSP the concentrations were 42.1 ± 22.6 and 6.1 ± 3.2 μg/m3 respectively. Both OC and EC exhibited a clear seasonal pattern with highest concentration observed in winter followed by summer and monsoon which may be due to the combined effect of changes in emission rates and different meteorology in various seasons. Diurnal variation indicated higher concentration during night in all seasons. TCA (Total carbonaceous aerosol) accounted for an averaged 50.3% of PM2.5 mass and 29.6% of TSP mass. The annual average OC/EC ratio was 6.6 which is similar ratio for biomass burning emissions. The SOC concentrations were found to be higher during winter season in both PM2.5 and TSP. To study the influence of natural singular events in aerosol composition, three types of episodic events have been identified. The SEM/EDX analysis revealed the dominance of carbonaceous particles during winter season which is also supported by back trajectory analysis which shows that the origin of these particles is mainly anthropogenic in nature.