PM 2.5 samples were collected at traffic, rural and campus sites in Agra during Nov 2010 to Feb 2011 and characterized for carbonaceous aerosols. The average mass concentrations of PM 2.5 were 308.3 ± 51.8 μg/m 3 , 91.2 ± 17.3 μg/m 3 and 140.8 ± 22.3 μg/m 3 at the traffic, rural and campus sites, respectively. The 24-h mass concentrations of PM 2.5 were significantly higher than the limit of 60 μg/m 3 prescribed in the National Ambient Air Quality Standards (Indian NAAQS) and 25 μg/m 3 of those of the WHO (World Health Organization). The average concentrations of OC (organic carbon) and EC (elemental carbon) were 86.1 ± 5.2 and 19.4 ± 2.4 at the traffic site, 30.3 ± 12.9 and 4.0 ± 1.5 at the rural site and 44.5 ± 18.5 μg/m 3 5.0 ± 1.4 μg/m 3 at the campus one. The contributions of TCA (Total Carbonaceous Aerosol) at the traffic, campus and rural sites were found to be 52, 54 and 58% of PM 2.5 mass, respectively. A significant correlation was observed between water soluble K + and OC at the rural (R 2 = 0.63) and campus (R 2 = 0.53) sites compared to the traffic one (R 2 = 0.35). This may be attributed to increased biomass burning emissions at the rural and campus sites. The concentrations of SOC (Secondary Organic Carbon) were estimated based on the minimum OC/EC ratio, and were found to be 15.3 ± 6.3, 8.2 ± 5.8 and 28.8 ± 15.8 μg/m 3 , accounting for 18, 24.7 and 60.7% of total OC at the traffic, rural and campus sites, respectively. The surface morphology of the particles was analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDX). The results indicated branched chain-like aggregates of carbon bearing spheres at the traffic and rural sites, while at the campus site carbon-rich and minerogenic (mineral dust) particles were the dominant ones.

Aerosol samples were collected during winter and summer season in Agra, India. The mass concentrations of TSP ranged from 206.1-380.5 μg/m 3 with the average concentration of 306.1 μg/m 3 . The seasonal average concentrations of TSP were 273.4 ± 85.5 μg/m 3 in summer and 338.6 ± 89.1 μg/m 3 in winter. The high levels of mass concentration during winter may be attributed to different emission sources and meteorological conditions at this time of year. The morphology, size and elemental composition of individual aerosol particles were examined using a scanning electron microscope (SEM) coupled with an energy dispersive X-ray system (EDX). The particles analyzed in the study were mostly of large size, with equivalent diameters ranging from 2 to 70 μm. Based on the results of the elemental composition and morphology, 3,500 particles were classified into three groups: biogenic aerosol, geogenic and anthropogenic particles. Different groups of particles have varied morphologies. The soil related aerosols were dominant during the sampling period, showing that crustal materials are the primary contributor to airborne particles at this site. A distinct seasonal variation in the amount of carbonaceous particles was observed. The significant increase in mineral dust particles found during summer may be attributed to the contribution of dust storms, which is also supported by a trajectory cluster analysis.

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This study presents a comprehensive set of 2 years of data (January 2009-December 2010) on the chemical composition of ambient aerosols collected at a university campus in Agra, which lies on the Indo-Gangetic Plain (IGP). The average concentration of total suspended particles (TSP) was 213. . The crustal source contribution was observed based on the ratios of various ions with respect to Ca in soil and aerosol. On the basis of backward trajectories and the associated concentrations of the ions, the aerosol samples were classified into sectors in relation to their origin to determine the related sources. The major sources of water soluble ions identified at Agra are biomass combustion and local soil.

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