Concentration and sources of atmospheric polycyclic aromatic hydrocarbons(PAHs) in PM_(2.5) in Beijing

Sixteen polycyclic aromatic hydrocarbons(PAHs) were determined by GC/MS in PM2.5 samples taken from September 2003 to July 2004 in Beijing.The annual average concentration of the total PAHs was 139.59 ng·m-3,ranging from 1.02 ng·m-3 to 776.4 ng·m-3 and showed strong seasonal variation,that is,the highest value in winter(271.05 ng·m-3) and the lowest in summer(26.10 ng·m-3).These results indicate the influence of both main source emission and meteorological conditions.Over the whole year,the average amounts of the different ring PAHs appeared in the following order:4-ring 5-ring 6-ring 3-ring 2-ring.In winter,the percentage of 4-ring PAHs was the highest(48.7%),followed by 5-ring PAHs(32.5%) and 6-ring PAHs(14.9%);in summer,the percentage of 5-ring and 6-ring PAHs(36.5%,together) were higher than 4-ring PAHs(24.1%).Results from both the characteristic ratios of sources and principal component analysis(PCA) indicated that coal burning,gasoline and diesel vehicle emissions were the three main sources of PAHs in PM2.5 in Beijing.These three sources can explain 88% of the total variance.