Atmospheric bulk deposition of PAHs over Brahmaputra valley: Characteristics and influence of meteorology

Abstract

Bulk atmospheric deposition of Polycyclic Aromatic Hydrocarbons (PAHs) in Guwahati city of the Brahmaputra Valley have been characterised for a period of one year. The ΣPAHs (USEPA’s priority 16) and benzo(s)pyrene (BaP) concentrations in the collected bulk deposit ranged between 2.2 and 1035 ng mL–1, and BDL and 5.6 ng mL–1 respectively. Greater deposition of PAHs was observed during the dry season and the deposition of low molecular weight PAHs (LMWPAHs) were particularly high. The study revealed explicit effect of the prevailing meteorology on the bulk atmospheric deposition characteristics of PAHs. Greater number of inversion days and lowering of inversion height during the dry season were found to enhance deposition of PAHs. Diagnostic ratios indicated pyrogenic origin of the PAHs derived from combustion of diesel, coal and wood combustion. The deposition of LMWPAHs was greatly influenced by temperature. The diurnal variation of relative humidity, and wind pattern were found to affect deposition of PAHs.