Chemical Constituents of Carbonaceous and Nitrogen Aerosols over Thumba Region, Trivandrum, India

Abstract

Aerosol filter samples collected at a tropical coastal site Thumba over Indian region were analysed for water-soluble ions, total carbon and nitrogen, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon/nitrogen and their sources for different seasons of the year. For the entire study period, the order of abundance of ions showed the dominance of secondary ions, such as SO42−, NO3−, and NH4+. On average, Mg2+ (56%), K+ (11%), SO42− (8.8%), and Ca2+ (8.1%) contributions were from maritime influence. There was significant chloride depletion due to enhanced levels of inorganic acids, such as SO42− and NO3−. Total carbon contributed 21% of the aerosol total suspended particulate matter in which 85% is organic carbon. Primary combustion-generated carbonaceous aerosols contributed 41% of aerosol mass for the entire study period. High average ratios of OC/EC (5.5 ± 1.8) and WSOC/OC (0.38 ± 0.11) suggest that organic aerosols are predominantly comprised of secondary species. In our samples, major fraction (89 ± 9%) was found to be inorganic nitrate in total nitrogen (TN). Good correlations (R2 ≥ 0.82) were observed between TN with NO3− plus NH4+, indicating that nitrate and ammonium ions account for a significant portion of TN. The temporal variations in the specific carbonaceous aerosols and air mass trajectories demonstrated that several pollutants and/or their precursor compounds are likely transported from north western India and the oceanic regions.