Stable Isotopic and Chemical Characteristics of Bulk Aerosols during Winter and Summer Seasons at a Station in Western Coast of India (Goa)

ABSTRACT

We measured stable isotopic and chemical characteristics of bulk aerosols collected at a coastal station in western India (Goa) between December 2009 and January 2011, to characterize lower tropospheric atmospheric conditions and their influence on particle chemistry during winter and summer seasons. Marked differences were observed in terms of sources and chemical compositions of bulk aerosols. The δ¹⁵N_TN values of winter aerosols (10.8 ± 2.2‰, n = 10) indicate biomass burning contributions in the carbonaceous fraction, while significantly depleted δ¹⁵N_TN values of summer aerosols (6.2 ± 2.3‰, n = 12) hints incorporation of marine N species. The δ³⁴S_TS showed depleted values during winter (5.0 ± 1.0‰, n = 10), which closely matched with those of typical urban polluted environments, while summer aerosols showed a systematic enrichment of δ³⁴S_TS (up to ~14‰ with average value 9.0 ± 2.8‰, n = 13); possibly due to incorporation of volatile dimethyl sulfide (DMS) and its precursor dimethylsulfoniopropionate (DMSP) dimethyl sulfide (DMS) emitted from the adjacent Arabian Sea. Likewise, δ¹³C_TOC values showed ~2‰ enrichment in winter aerosols (–24.8 ± 0.4‰, n = 10) with respect to those of summer values, indicating presence of bio-fuel and coal burning contributions in carbonaceous fraction of winter aerosols. We also measured major ions (Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺, NH₄⁺, Cl^–, Br^–, NO₃^–, SO₄^–2) in water soluble fraction of aerosols to understand winter/summer changes in the atmospheric chemistry over this coastal area. This is the first ever dataset on triple isotopic characteristics of bulk aerosols at a coastal location of India showing signatures of continental bio-mass/bio-fuel burning influences during winter, whereas marine inventories (e.g., sea salt, DMS and mineral dust) appear to dominate chemical composition of summer aerosols.