Characterization And Source Apportionment Analysis Of PM_2.5 Associated Polycyclic Aromatic Hydrocarbons （PAHs） In Nanjing

In order to explore the distribution characteristics and the emission sources of PAHs, sampling of PM2.5 are conducted constantly in NUIST in the suburban site of Nanjing using aerosol sampler in four seasons of 2014.18 kinds of PAHs were analyzed with the emphasis on the factors which affect the PAHs concentrations around the Spring Festival. And PAHs concentrations of August 2013 in the urban area of Nanjing are analyzed to study the effect of temporary emission reduction measures on PAHs in atmospheric PM2.5. Research results show that:(1) The T-PAHs concentration in the NUIST show the trendency of winter> spring> autumn> winter. The main PAHs species of the four seasons are similar, which indicates that the dominant source of PAHs in the four seasons is the vehicle emission. Regardless of the season, the highest proportion is high molecular weight, accounting for 53.7-80.6% of T-PAHs. The proportion of semi-volatile medium molecular weight PAHs in winter was significantly higher than that in other seasons, which was related to the partitioning of PAHs from gas to particle phase. The low molecular weight of PAHs was higher in autumn and winter.(2) The averaged PAHs for pre-SF, SF and after SF periods were 50.6,17.2 and 29 ng m-3. When comparing PAHs during Chinese New Year (CNY) day with intensive fireworks burning with the day before CNY, PAH mass concentrations increased obviously especially for HMW-PAHs by 13.8 times. Combustion-derived PAHs and carcinogenic PAHs also increased, by 8.7 and 13.8 times, indicating more pyrolysis PAHs formed during CNY and they were highly carcinogenic.Considering the influence of air masses origin, PAH concentrations exhibited decreasing trend when air masses originated and transported across North China Plain, Central China, Shandong Peninsula, Northwest China and Sea. PAH concentrations exhibited decreasing trend as haze> fog-haze>clear>fog day. Significant negative correlations were found between mixing layer height and relative humidity while no correlations existed between wind, speed, temperature and PAH concentrations in this study. Diagnostics ratios and principal component analysis (PCA) indicated that coal combustion, traffic emissions, industrial processes and petroleum for non-SF holiday days were the main sources of PM2.5 associated PAHs. The contributions of coal combustion and vehicle emission during SF decreased by 10%, when compared with those during pre-SF period.(3) The total concentration of analyzed PAHs during the 2013 Asian Youth Games period in Nanjing ranged from 3.87 ng m-3 to 15.6 ng m-3, with 5-ring PAHs (39.5±4.8% of total PAHs) and 6-ring PAHs (22.8±3.4%) dominated. The ratio of PAHs (3+4) to PAHs (5+6) was in the range of 0.25-1.35 indicating that PAHs might be emitted mostly from the local emissions. The average mass concentrations of PAHs, LMW-PAHs, MMW-PAHs, HMW-PAHs and COMPAHs for the during-AYG period were all lower than those for pre-AYG and post-AYG periods, due to the emission control measures. The main emission sources of PM2.5-bound PAHs were identified by diagnostic ratios and principal component analysis, which were gasoline vehicle emissions, coal combustion and petroleum. The estimated lifetime cancer risks of PAHs during the Asian Youth Games were comparable to the acceptable levels of 10-6 to 10-4. And they decreased by 23% and 27% for children and adults when compared with those for pre-AYG and post-AYG period, indicating the effectiveness of emission control measures during AYG period.