Seasonal variation and source apportionment of organic and inorganic compounds in PM2.5 and PM10 particulates in Beijing, China

The distribution and source of the solvent-extractable organic and inorganic components in PM_2.5 (aerodynamics equivalent diameter below 2.5 microns), and PM₁₀ (aerodynamics equivalent diameter below 10 microns) fractions of airborne particles were studied weekly from September 2006 to August 2007 in Beijing. The extracted organic and inorganic compounds identified in both particle size ranges consisted of n-alkanes, PAHs (polycyclic aromatic hydrocarbons), fatty acids and water soluble ions. The potential emission sources of these organic compounds were reconciled by combining the values of n-alkane carbon preference index (CPI), %waxC_n, selected diagnostic ratios of PAHs and principal component analysis in both size ranges. The mean cumulative concentrations of n-alkanes reached 1128.65 ng/m³ in Beijing, 74% of which (i.e., 831.7 ng/m³) was in the PM_2.5 fraction, PAHs reached 136.45 ng/m³ (113.44 ng/m³ or 83% in PM_2.5), and fatty acids reached 436.99 ng/m³ (324.41 ng/m³ or 74% in PM_2.5), which resulted in overall enrichment in the fine particles. The average concentrations of SO₄²⁻, NO₃⁻, and NH₄⁺ were 21.3 ± 15.2, 6.1 ± 1.8, 12.5 ± 6.1 μg/m³ in PM_2.5, and 25.8 ± 15.5, 8.9 ± 2.6, 16.9 ± 9.5 μg/m³ in PM₁₀, respectively. These three secondary ions primarily existed as ammonium sulfate ((NH₄)₂SO₄), ammonium bisulfate (NH₄HSO₄) and ammonium nitrate (NH₄NO₃). The characteristic ratios of PAHs revealed that the primary sources of PAHs were coal combustion, followed by gasoline combustion. The ratios of stearic/palmitic acid indicated the major contribution of vehicle emissions to fatty acids in airborne particles. The major alkane sources were biogenic sources and fossil fuel combustion. The major sources of PAHs were vehicular emission and coal combustion.