| Polycyclic aromatic hydrocarbons(PAHs),a group of trace organic pollutants with carcinogenic and teratogenic properties,are widely present in the environment and are an important component of atmospheric organic aerosols.In addition,some derivatives of PAHs,such as halogenated PAHs(ClPAHs and BrPAHs),nitriated and oxygenated PAHs(NPAHs and OPAHs),which may be more toxic than their corresponding parent PAHs,have received sustained attention from domestic and international scholars.Industrial emissions are one of the most important anthropogenic sources of PAHs and their derivatives.Knowledge of the presence,composition,mechanisms and sources of these toxic chemicals in the ambient air near industrial areas is important for the control and management of pollutants.In this study,we collected a total of 48 passive air samples using a passive air sampler(PUF-PAS)during the heating period(December 7,2019 to April 15,2020)and the non-heating period(June 2,2020 to October 4,2020)at 24 sampling sites near typical heavy industrialized areas(steel plants,chemical plants,and rubber plants)in North China.18 PAHs,16 BrPAHs,8 ClPAHs,17 NPAHs and 6 OPAHs were analyzed using gas chromatography/mass spectrometry(GC/MS),and the concentration levels,molecular composition,formation mechanisms,potential sources and toxicity of these toxic compounds were studied.During the two sampling periods,the average concentrations of PAHs,BrPAHs,ClPAHs,NPAHs and OPAHs were 63.1±49.5 ng/m3,471±357 pg/m3,229±145 pg/m3,312±299 pg/m3 and 2120±1307 pg/m3,respectively.Except for NPAHs,BrPAHs,ClPAHs,OPAHs,and PAHs all showed higher levels during the heating period.The average concentrations of NPAHs were comparable between the two sampling periods,which was associated with elevated concentrations of 1N-NAP and 2N-NAP of 2 rings during the non-heating period.The spatial distributions of PAHs,BrPAHs,ClPAHs,NPAHs and OPAHs showed similar patterns,with higher pollution levels at sampling points closer to the steel plant.The average concentrations of PAHs,BrPAHs,ClPAHs,NPAHs and OPAHs were higher in industrial areas than in rural areas.Congener composition distribution of PAH derivatives shows the domination of mono-substituted low molecular weight compounds(2～3 rings),and this trend confirms that PUF-PAS collects more volatile compounds,which are mainly present in the gas phase.In this study,the major formation mechanism of halogenated PAHs was discussed by correlation analysis and Gibbs free energy,indicating that the direct bromination reaction of parent PAHs may be the major formation mechanism of BrPAHs.Furthermore,the characteristic ratio of 2+3N-FLT/1N-PYR indicates that NPAHs in this study mainly derived from primary emission sources during both sampling periods,but the contribution of secondary formation of NPAHs may increase at the heavily contaminated sites.The quantified analysis of potential sources of PAHs,Br/ClPAHs and N/OPAHs were performed by the positive matrix factor model(PMF),and the results showed that the main sources of PAHs were:industrial emissions and coal combustion sources(42%)>biomass combustion sources(29%)>vehicle emission sources(18%)>crude oil and petroleum volatilization sources(11%);the main sources of Br/ClPAHs were:industrial and combustion sources(41%)>photochemical reaction sources(18%)>two other sources(41%);the main sources of N/OPAHs are:coal and biomass combustion sources(46%)>secondary formation reaction sources(33%)>traffic emission sources(21%).The toxicity evaluation of PAHs and their derivatives was carried out based on toxicity equivalent quantities of the compounds.PAHs derivatives,especially BrPAHs and ClPAHs,exhibited high levels of toxicity even at lower concentrations.Overall,this study provides important data for understanding the different atmospheric behaviors and health risks of PAHs and their derivatives. |
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