Atmospheric particulate matter (PM2.5), EC, OC, WSOC and PAHs from NE-Himalaya: abundances and chemical characteristics

Atmospheric concentrations of elemental, organic and water-soluble organic carbon (EC, OC and WSOC) and polycyclic aromatic hydrocarbons (PAHs) have been studied in PM2.5 (particulate matter of aerodynamic diameter <= 2.5 mu m) from a site (Barapani: 25.7 degrees N; 91.9 degrees E; 1 064 m amsl) in the foot-hills of NE-Himalaya (NE-H). Under favorable wind-regimes, during the wintertime (January-March), study region is influenced by the long-range transport of aerosols from the Indo-Gangetic Plain (IGP). For rest of the year, ambient atmosphere over the NE-H is relatively clean due to frequent precipitation events associated with the SW-and NE-monsoon. The concentration of PM2.5 over NE-H, during the wintertime, varied from 39-348 mu g m(-3), with average contribution of OC and EC as 36 +/- 8% (AVG +/- SD) and 6 +/- 3%, respectively. For the OC/EC ratio as high as 10-15 (relatively high compared to fossil-fuel source) associated with WSOC/OC ratio exceeding 0.5 in NE-H, it can be inferred that dominant source of carbonaceous aerosols is attributable to biomass burning emissions and/or contributions from secondary organic aerosols (SOA). The OC/PM2.5 ratio from NE-H is somewhat higher compared to upwind regions in the IGP (Range: 0.16-0.24). The abundance of Sigma PAHs show large variability, ranging from 4-46 ng m(-3), and the ratio of sum of 4- to 6-ring PAHs (Sigma((4-) to (6-)) PAHs) to EC is 2.4 mg g(-1); similar to that in the upwind IGP and is about a factor of two higher than that from the fossil-fuel combustion sources. The cross-plot of PAH isomers [FLA/(FLA+PYR) vs. ANTH/(ANTH+PHEN), BaA/(BaA+CHRY+TRIPH), BaP/(BaP+B[b,j,k]FLA) and IcdP/(IcdP+BghiP)] reaffirms the dominant impact of biomass burning emissions. These results have implications to large temporal variability in aerosol radiative forcing and environmental change over the NE-Himalaya.