[1] Synchronous sampling of bulk-aerosols, carried out during wintertime from the two strategically located sites in North India, reveals that total suspended particulates (TSP) over an urban site (Hisar: 29.2°N 75.7°E; 219 m asl) ranged from 67 to 396 mg m À3 ; in contrast, TSP at Manora Peak (a high-altitude station: 29.4°N 79.5°E; 1950 m asl) was relatively low (range: 13.7 to 42.7 mg m À3 ). At Hisar, on average, water-soluble ionic species (WSIS, range: 14.1 to 78.3 mg m À3 ) contribute nearly one-fourth by weight to TSP, with dominant contribution from SO 4 2À , NO 3 À and NH 4 + . The time series analysis over a span of 30 days shows somewhat uniform distribution of organic carbon/elemental carbon (OC/EC) ratio centering around 8.5 ± 2.2 at this urban site; and the water-soluble organic components (WSOC range: 6.7 to 42.0 mg m À3 ) account for 11.5 % to the TSP concentration. Both WSOC and OC exhibit significant positive correlation with water-soluble K + (r = 0.88 and 0.79 respectively), suggesting their dominant contribution from biomass burning. At Manora Peak, the chemical composition of ambient aerosols show characteristically lower abundances of WSIS (range: 2.0 to 9.9 mg m À3 ) and WSOC (range: 1.4 to 6.0 mg m À3 ); together they account for one-third of the TSP. The characteristic low abundances of OC (range: 2.8 to 6.9 mg C m À3 ) and EC (range: 0.34 to 1.4 mg C m À3 ) at this high-altitude site and their significant correlation with K + and SO 4 2À suggest contribution from long-range transport of anthropogenic species. This study represents a first comprehensive data set for documenting the chemical characteristics of ambient aerosols and source apportionment of EC, OC, WSIS and mineral dust over urban and high-altitude sites in north India, an important data set required for the south Asian region. If the observed OC/EC ratios far greater than $2 (unlike reported values in the literature for urban sites) and the semi-empirical estimates of secondary OC are typical of the annual average abundances in the ambient aerosols over north India, then the temporal and regional analyses of primary and secondary OC using the existing emission models require reassessment for this region.Citation: Rengarajan, R., M. M. Sarin, and A. K. Sudheer (2007), Carbonaceous and inorganic species in atmospheric aerosols during wintertime over urban and high-altitude sites in North India,

The chemical composition of aerosols in the Marine Atmospheric Boundary Layer (MABL) of Bay of Bengal (BoB) and Arabian Sea (AS) has been studied during the spring and inter-monsoon (March-May 2006) based on the analysis of water soluble constituents (Na + , NH in BoB and exhibit a decreasing trend from north to south; however, abundance of these carbonaceous species are not significantly pronounced over AS. The abundance of Al, used as a proxy for mineral aerosols, varied from 0.2 to 1.9 μg m −3 over BoB and AS, with a distinctly different spatial pattern -decreasing north to south in BoB in contrast to an increasing pattern in the Arabian Sea.

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The chemical composition of total suspended particulate (TSP) matter and secondary aerosol formation have been studied during wintertime fog and haze events from urban sites (Allahabad and Hisar) in the Indo-Gangetic Plain. The atmospheric abundances of elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC) suggest that organic matter is a major component of TSP, followed by concentrations of sulphate and nitrate under varying meteorological conditions. The concentrations of EC, OC, and WSOC show a nearly 30% increase during fog and haze events at Allahabad and a marginal increase at Hisar; whereas inorganic constituents (NH 4 + , NO 3 − and SO 4 2− ) are 2-3 times higher than those during clear days at both the locations. The sulphur and nitrogen oxidation ratios (SOR and NOR) also exhibit significant increases suggesting possible enhancement of secondary formation of SO 4 2− and NO 3 − during fog and haze events. The significant correlation between NH 4 + -SO 4 2− (R 2 = 0.66, n = 61) and an NH 4 + /SO 4 2− equivalent ratio ≥ 1 during fog-haze conditions suggest nearcomplete neutralization of sulphuric acid by ammonia. In contrast, NH 4 + /SO 4 2− equivalent ratios are less than 1 during normal days suggesting an NH 3 -deficient environment and the possible association of SO 4 2− with mineral dust for neutralization. Secondary inorganic aerosol formation and their hygroscopic growth can have significant impact on atmospheric chemistry, air-quality and visibility impairment during fog-haze events over northern India.