Chemical characterization of PM 2.5 collected from a rural coastal island of the Bay of Bengal (Bhola, Bangladesh)

Abstract

This work focuses on the chemical characterization of fine aerosol particles (PM_2.5) collected from a rural remote island of the Bay of Bengal (Bhola, Bangladesh) from April to August, 2013. PM_2.5 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 PM_2.5 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 PM_2.5 mass. Secondary organic carbon (SOC) was inferred to be ~ 26% of OC. The sum of ions comprised ~ 27% of PM_2.5 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).