Long-term seasonal variability in the water-soluble inorganic composition of coarse and fine aerosols over the northeast Arabian sea
Abstract
The chemical composition of atmospheric aerosols plays a crucial role in understanding air quality, climate interactions, and oceanic biogeochemical cycles. This study presents a comprehensive long-term seasonal analysis (December 2017–May 2022) of water-soluble inorganic composition (WSIC) in coarse (PM10) and fine (PM2.5) aerosols over a tropical coastal site located in the northeast Arabian Sea (Goa, India). A total of 583 aerosol samples (290 p.m.10 and 293 p.m.2.5) were simultaneously collected and analysed for major cations (Na+, NH4+, K+, Mg2+, Ca2+) and anions (Cl−, NO3−, SO42−). The seasonal variability in WSIC was found to be strongly influenced by continental outflows, monsoonal dynamics, and marine sources. The highest WSIC concentrations were observed during winter (23.1 μg m−3 for PM10 and 16.2 μg m−3 for PM2.5) season which was attributed to anthropogenic emissions and secondary inorganic aerosol formation, while lower values were observed during summer months mainly due to dilution effects caused by strong marine air intrusion. Non-sea-salt sulphate (nss-SO42-) dominated both aerosol fractions (>98 %) while nitrate (NO3−) was dominant particularly in summer due to its interaction with long-range transported mineral dust. Ammonium (NH4+) correlated strongly with sulphate (r > 0.9) in winter and post-monsoon, indicating ammonium sulphate as a major component of secondary aerosols. Crustal elements (Ca2+, Mg2+) were more prominent in PM10, peaking in summer due to long-range dust transport. Biomass burning tracers (nss-K+) were significantly higher (p < 0.05) in PM2.5 during winter, emphasizing regional agricultural residue burning as a key source from the northern regions in the Indo-Gangetic Plains. Global reanalysis datasets (MERRA-2, CAMS) effectively captured sulphate trends but overestimated sea salt concentrations. These findings provide critical insights into aerosol chemistry in a tropical coastal environment and its implications for air quality and climate modeling. Regional scale chemical characterisation of aerosols is important for their better parameterization in chemical transport models.
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