Seasonal trends in chemical composition of aerosols at a tropical coastal site of India

<jats:p>Chemical composition of near‐surface aerosols at the tropical coastal location Trivandrum (8.55°N, 77°E) has been studied by analyzing the aerosol samples collected during a period of 16 months from October 2003 to January 2005. The annual mean aerosol mass loading at this site averages to around 54 ± 19 <jats:italic>μ</jats:italic>g m<jats:sup>−3</jats:sup>. The chemical analysis of samples revealed Cl<jats:sup>−</jats:sup>, SO<jats:sub>4</jats:sub><jats:sup>2−</jats:sup>, and NO<jats:sub>3</jats:sub><jats:sup>−</jats:sup> to be the major anionic species and Na, NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>, Fe, and Ca to be the major cationic species. The total mass loading and the mass concentration of various chemical species showed pronounced seasonal dependence. The active aerosol sources at this location have been investigated in detail to delineate their relative dominance in different seasons. Ions like Na, Cl, Mg, and K, which are mainly of oceanic origin, showed peak during monsoon, indicating sea spray to be the most important source mechanism during the period. On the other hand, mass loading of SO<jats:sub>4</jats:sub><jats:sup>2−</jats:sup>, NH<jats:sub>4</jats:sub><jats:sup>+</jats:sup>, PO<jats:sub>4</jats:sub><jats:sup>3−</jats:sup>, Fe, and Al and that of trace elements exhibited their maximum in winter/summer, indicating the dominance of continental/crustal sources during the period. The sea salt and non‐sea salt components of individual ions like SO<jats:sub>4</jats:sub><jats:sup>2−</jats:sup>, K, Ca, and Mg also revealed distinctly different seasonal patterns. In spite of being a coastal site, the non‐sea salt components dominated at this location. Dominance of non‐sea salt SO<jats:sub>4</jats:sub><jats:sup>2−</jats:sup> throughout the year indicates significant anthropogenic influence at this location. On the basis of this study, a first‐cut model for the chemical composition of aerosols at this tropical coastal site has been evolved.</jats:p>