Chemical characterization of PM2.5 collected from a rural coastal island of the Bay of Bengal (Bhola, Bangladesh).

This work focuses on the chemical characterization of fine aerosol particles (PM2.5) collected from a rural remote island of the Bay of Bengal (Bhola, Bangladesh) from April to August, 2013. PM2.5 particle-loaded filters were analyzed for organic carbon (OC), elemental carbon (EC), water-soluble ions, and selected saccharides (levoglucosan, mannosan, galactosan, arabitol, and mannitol). The average PM2.5 mass was 15.0 ± 6.9 μg m-3. Organic carbon and elemental carbon comprised roughly half of the analyzed components. Organic carbon was the predominant contributor to total carbon (TC) and accounting for about 28% of PM2.5 mass. Secondary organic carbon (SOC) was inferred to be ~ 26% of OC. The sum of ions comprised ~ 27% of PM2.5 mass. The contribution of sea salt aerosol was smaller than expected for a sea-near site (17%), and very high chloride depletion was observed (78%). NssSO42- was a dominant ionic component with an average concentration of 2.0 μg m-3 followed by Na+, NH4+, and nssCa2+. The average concentration of arabitol and mannitol was 0.11 and 0.14 μg m-3, respectively, while levoglucosan and its stereoisomers (mannosan and galactosan) were bellow detection limit. NH4+/SO42- equivalent ratio was 0.30 ± 0.13 indicating that secondary inorganic aerosol is not the main source of SO42-. Enrichment factor (EF) analysis showed that SO42- and NO3- were enriched in atmospheric particles compared to sea aerosol and soil indicating their anthropogenic origin. Higher OC/EC ratio (3.70 ± 0.88) was a good indicator of the secondary organic compounds formation. Other ratios (OC/EC, K+/EC, nssSO42-/EC) and correlation analysis suggested mixed sources for carbonaceous components. Arabitol and mannitol both showed strong correlation with EC having R 2 value 0.89 and 0.95, respectively. Air mass trajectories analysis showed that concentrations of soil and anthropogenic species were lower for air masses originating from the sea (May-August) and were higher when air came from land (April).