The Characteristics And Sources Of Atmospheric PAHs And Their Nitrated And Oxygenated Derivatives In An Urban Area Of Chongqing

Polycyclic aromatic hydrocarbons(PAHs)are the most important group of toxic and harmful substances in the atmosphere due to their extensive sources,persistence in the environment,earcinogenicity,mutagenicity and teratogenicity.PAHs have been found to be associated with atmospheric particulate matter,particularly fine particles.In recent years,oxygenated PAHs(OPAHs)and nitrated PAHs(NPAHs)in the atmosphere have been studied because they are more toxic than the parent PAHs and have direct mutagenicity.Chongqing is one of the most densely populated cities in southwestern China.With the rapid development of industrialization and urbanization in recent years,population and energy demand have increased greatly,and air pollution in Chongqing has become a serious problem.The mountainous geographical conditions as well as high-temperature and high-humidity climatic characteristics have led to more stagnant weather condition in Chongqing,which may enhance air pollution and affect the environmental behavior of atmospheric pollutants.In this study,we collected gaseous and particulate samples as well as size-segregated particle samples in the spring,summer,autumn and winter of 2016 in an urban area of Chongqing.We studied the concentrations,sources,health risks of PAHs,OPAHs and NPAHs,most importantly,discussed their gas-particle partitioning and size distribution in detail.(1)The concentrations of 30 parent polycyclic aromatic hydrocarbons(PAHs),10 oxygenated PAHs(OPAHs)and 27 nitrated PAHs(NPAHs)were measured in the atmosphere of a Chongqing urban area.The annual average(gaseous and particulate)concentrations of OPAHs and PAHs were close,which were 79.9±40.5 ng/m3 and 93.7±75.2 ng/m3,respectively,and was one to two orders of magnitude higher than the concentration of NPAHs(1.65±1.43 ng/m3).The concentration of primary emitted PAHs was highest in winter and lowest in summer.While concentrations of OPAHs and NPAHs were higher in summer than autumn and spring,attributing to the contribution of secondary formation in summer.(2)Diagnostic ratios were used to analyze the sources of PAHs and their derivatives in the urban area of Chongqing.The results show that biomass burning,coal combustion and petroleum combustion are the main sources of PAHs.The ratios of 2-NFLT/1-NPYR indicate that the secondary formation of NPAHs contributes significantly in summer,and primary emissions are dominated in winter.The ratios of OPAHs/PAHs in winter are close to those freshly emitted from primary emissions,but higher than those values in summer,indicating the contribution of secondary formation n summer.(3)Target compounds with molecular weight less than 209 g/mol are mainly present in the gas phase,and compounds with molecular weight higher than 229 g/mol are mainly present in the particle phase.By fitting the linear relationship between the measured logKP and logPLo of target compounds,it is found that the slope of the PAHs(-0.61--0.52)is shallower than the slope of OPAHs and NPAHs(-2.14--0.73),indicating adsorption process might be more important for OPAHs and NPAHs than PAHs.Moreover,the absorption model,adsorption model and Dual model were used to simulate the gas-particle partitioning of PAHs,OPAHs and NPAHs in the atmosphere.The results show that the three models well predicted the particle-bound fractions and logKP of PAHs.However,they all underestimated the logKp of OPAHs and NPAHs.This discrepancy may be attributed to the higher relative humidity in Chongqing,which may lead to higher water content in particles.This may have stronger impact on less hydrophobic compounds,e.g.,OPAHs and NPAHs.(4)The size-segregated particulate concentrations of PAHs,OPAHs and NPAHs in the urban area of Chongqing were determined in the present study.The results showed that target compounds was mainly associated with particles with aerodynamic equivalent diameter less than 2.1 ?m,indicating that most of the polycyclic aromatic compounds could be inhaled into the deepest part of the human respiratory system.The particle size distribution of PAHs and OPAHs is unimodal with peaks at<0.4 ?m and 0.4-0.7 ?m,respectively.The particle size distribution of NPAHs is bimodal,with a major peak at 0.4-0.7 ?m and a second at 3.3-4.7?m.NPAHs at 3.3-4.7 ?m is dominated by high molecular weight compounds.The ratios of NPAHs/PAHs and OPAHs/PAHs have a peak at 3.3-4.7 ?m,indicating emission from primary non-combustion processes.(5)The toxicity equivalent concentration(TEF)was used to calculate the toxic equivalent concentrations of PAHs in the urban atmosphere of Chongqing,as well as the excess inhalation cancer risk assessment.The total excess inhalation cancer risk,including 19 PAHs,2 OPAHs and 9 NPAHs,is 1.97×10-5 by applying the unit risks suggested by the Offiee of Environmental Health Hazard Assessment(OEHHA).The excess inhalation cancer risk in the particulate phase accounted for 97.34%,99.17%and 85.50%of the total risk in the atmosphere for PAHs,OPAHs and NPAHs,respectively,indicating that the carcinogenicity of these compounds was mainly associated with the particle phase.In addition,it is found that the cancer risk of PAHs and its derivatives in the particles is mainly concentrated in the particles with size less than 1.1 ?m.The total cancer risk was higher in autumn and winter than spring and summer,suggesting that it is imperative to control the concentrations of fine particles in the autumn and winter.