Chemical characteristics of submicron particles in winter in Xi'an

Daily submicron aerosol samples (PM₁, particles less than 1 μm in diameter) were collected continuously from Dec. 1 to Dec. 31, 2006 and the concentrations of 11 water-soluble ions (Na⁺, NH⁺, K⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, Br^-, NO^2- NO3^- and SO4^2-) and elemental carbon (EC) and organic carbon (OC) were determined in the filter samples to characterize the chemical composition of PM₁ over Xi'an during winter. The mean PM₁ mass concentration was 149.7 μg/m ³. Water-soluble ions were dominant chemical species and occupied to 46% of PMi mass. Na⁺, NH4⁺, Ca²⁺, Cl ^-, SO4^2- and NC^- were the major species of ionic compounds, which accounted for 95.3% of total ions concentration. The average OC and EC concentrations were 23.7 ± 10.27 μg/m³ and 4.6 ± 1.8 μg/m³, respectively. Carbonaceous aerosol is another major component of PM₁, and total carbonaceous aerosol occupied to 27.5% of PMi mass. High OC and OC/EC ratio were found in Xi'an in comparison with the past studies in Hong Kong and Taipei. Factor analysis on the eight carbon fractions shows that coal combustion and gasoline automobile exhaust, diesel automobile exhaust, and biomass burning were found to be statistically significant and explained 93% of the carbonaceous aerosols contributions.