Characteristics And Sources Of PM_2.5-bound Polycyclic Aromatic Hydrocarbon （PAHs） In North China In Summer

To understand the characteristics of atmospheric PM2.5-bound PAHs in North China in summer, a field observation in June 2013 was carried out using a medium-volume PM2.5 sampler to collect PM2.5 samples. We used gas chromatography/mass spectrometry (GC/MS) to analyze sixteen kinds of optimal control PAHs and studied the concentrations, composition, sources and toxicity of atmospheric PM2.5-bound PAHs in biomass burning day, heavily polluted day and slightly polluted day in North China in summer. The main conclusions were as follows:(1) The average concentration of atmospheric PM2.5-bound PAHs in 2013 in North China in summer was 32.36 ng/m3. The average concentration of atmospheric PM2.5-bound PAHs in biomass burning day, heavily polluted day and slightly polluted day in Yucheng and biomass burning day in Xianghe were 32.55 ng/m3,36.21 ng/m3, 25.86 ng/m3 and 34.81 ng/m3, respectively. The concentrations of atmospheric PM2.5-bound PAHs in heavily polluted day in Yucheng is the highest, the concentrations in biomass burning day in Yucheng and Xianghe was lower and the lowest concentrations was in slightly polluted day.(2) The highest proportion of atmospheric PM2.5-bound PAHs in North China in summer were high molecular weight PAHs (from 45.28% to 67.08%). The combusted PAHs accounted for 67.41% to 77.17%, which suggested the main pollution source in North China was combustion source. Atmospheric PM2.5-bound carcinogenic PAHs accounted for 10.77% to 17.12%, which should be achieved highly attention. BkF was the main PAHs species in all weather conditions. Flu (9.01%-9.76%), Flt (7.33%-11.59%), InP (8.44%-10.63%) and BgP (8.21%-9.46%) were main PAHs in biomass burning day, heavily polluted day and slightly polluted day in Yucheng.(3) There was no obvious difference in diurnal variation in the conditions of heavily polluted day and slightly polluted day in Yucheng and biomass burning day in Xianghe. But the concentrations of atmospheric PM2.5-bound PAHs in the nighttime (36.63 ng/m3) was obviously higher than that in daytime (28.47 ng/m3) during biomass burning day in Yucheng, which may be influenced by increase of pollutants diffusion in unstable atmospheric conditions in the daytime and the influence of long distance transport of biomass burning which mainly occurred at night. The studies about meteorological factors showed that there was negative correlation between the wind speed and the concentrations of PAHs.(4) The result of PCA showed that traffic emissions, biomass burning and coal combustion were the main atmospheric PM2.5-bound PAHs source in North China. We used diagnostic ratios and back-trajectory calculations to judge the sources of PAHs in different weather conditions. The main sources of atmospheric PM2.5-bound PAHs during biomass burning day in Yucheng were biomass burning, coal combustion and mixed with liquid fossil fuels combustion. Biomass burning was mainly affected by the dense straw burning in Shandong, Hebei and Jiangsu provinces. The main sources of atmospheric PM2.5-bound PAHs in heavily polluted day in Yucheng were fossil fuels combustion, biomass burning and coal combustion, and the industrial emissions sources in Beijing-Tianjin-Hebei region and Bohai Bay area had obvious impact on it. The main source of atmospheric PM2.5-bound PAHs in slightly polluted day in Yucheng were fossil fuels combustion, biomass burning and coal combustion, but the mass from the ocean would dilute the concentrations of atmospheric PM2.5-bound PAHs, so the concentations were the lowest. The concentrations of atmospheric PM2.5-bound PAHs in Xianghe were also affected by the long distance transport of straw burning in Shandong province and Jiangsu Province, but it was significantly affected by industrial pollution in Beijing-Tianjin-Hebei region.(5) The average toxic equivalent concentration of atmospheric PM2.5-bound PAHs in North China in different weather conditions was 5.54 ng/m. The highest toxic equivalent concentrations was in biomass burning day in Xianghe, which was 1.6 times higher than that in biomass burning day in Yucheng. In Yucheng, the highest toxic equivalent concentrations was in heavily polluted day (6.16 ng/m), which was 1.5 times higher than that in slightly polluted day (4.21 ng/m3), indicating that there were serious damage on human health in heavily polluted day. In the four conditions, the toxic equivalent concentration of 5-6 rings PAHs accounted for more than 95%, which suggested that high molecule weight PAHs contributed most in the total toxic equivalent concentration. The average level of carcinogenic risk in biomass burning day in Yucheng, biomass burning day in Xianghe, heavily polluted day in Yucheng and slightly polluted day in Yucheng were 1.68×10-6、2.68×10-6、2.28×10-6 and 1.55×10-6, which idicated potential carcinogenic risk, and the carcinogenic risk increased with the increase of age markedly.