Biomass burning influences determination based on PM2.5 chemical composition combined with fire counts at southeastern Tibetan Plateau during pre-monsoon period

Influences of biomass burning (BB) on a high altitude site were investigated by collecting fine particulate matter (PM2.5) samples from 29 March to 27 April of 2012 at Mt. Yulong (4500 m above sea level), and analyzing them for selected chemical species including water soluble ions (WSIs), organic carbon (OC), elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs) and n-alkanes. The mean PM2.5 mass loading for the study was 6.30 +/- 4.90 pg m(-3), and 15.48 +/- 2.82 pg m(-3) and 1.75 +/- 0.41 mu gm(-3) for a high and a low PM episode, respectively. WSIs accounted for 62% of the total mass, and SO42- was the dominant anion and NH4+ was the main cation. PAHs were mainly 3 ring compounds, fluorene (Flo) and phenanthrene (Phe) together accounted for 54% of the total PAHs. For n-alkanes, n-Nonacosane (C-29) concentration was the highest with the value of 1.09 +/- 1.18 ng m(-3), following is n-Hentriacontane (C-31) and n-Heptacosane (C-27) suggested that n-alkane in our samples were mainly contributed by biogenic sources. BB emission was confirmed by the diagnostic ratios, and it also had a significant influence on aerosol optical depth (AOD) distribution and enhances the concentration of most species, especially for OC, K+ and EC. Significant relationships were found between daily fire counts and BB species, and correlation coefficients (r) for mass, K+, OC, and EC were 0.58, 0.57, 0.53 and 0.60 (n = 29, P < 0.01), respectively. It indicated that daily fire counts can advance our understanding of how biomass burning affect aerosols and air quality at a high-altitude site