| Polycyclic aromatic hydrocarbons(PAHs),nitropolycyclic aromatic hydrocarbons(NPAHs)and nitrated aromatic compounds(NACs)are three aromatic compounds(ACs)in the atmosphere.Due to their widespread presence in atmospheric particulate matter and their important effects on ambient air quality,climate change and human health,they have attracted a lot of attention.In order to study the pollution characteristics,sources,and health risks of these three ACs in atmospheric particulate matter under complex anthropogenic emissions and meteorological conditions,PM2.5 samples and graded particle size samples were collected in urban Beijing from 2017 to 2018.Sixteen PAHs,Sixteen NPAHs and nine NACs were determined by gas chromatography-mass spectrometry(GC-MS).Combined with the other air pollution components and meteorological parameters during the observation period,the pollution characteristics and sources were analyzed by diagnostic ratios,correlation analysis and positive matrix factorization(PMF).Moreover,the health risks of PAHs and NPAHs were evaluated by the equivalent toxicity method(TEQBap)and the incremental lifetime cancer risk(ILCR),and the effects of NO2 and relative humidity(RH)on secondary formation of NPAHs and NACs were discussed.The main research conclusions are as follows:(1)The concentrations and components of PAHs and NPAHs in atmospheric particulate matter in urban Beijing showed obvious seasonal and diurnal variations during 2017-2018.During the sampling period,the concentrations of PAHs and NPAHs were the highest in winter,which were 77.92 ± 54.62 ng m-3 and 960.50 ± 697.55 pg m-3,respectively,and the lowest in summer,which were 5.58± 1.76 ng m-3 and 76.04±31.52 pg m-3,respectively.Fluoranthene and pyrene were the most abundant PAHs in spring and summer,respectively,while benzo[b]fluoranthene was the richest in autumn and winter.9-nitroanthracene was the dominant NPAHs species in spring,summer and winter,while 2-nitropyrene was most abundant in autumn.Diurnal variation analysis showed that the concentrations of PAHs and NPAHs were 2-3 times higher at night than during the day.In addition,NPAHs were mainly distributed on fine particles(Dp<1.1 μm),showing unimodal and bimodal distribution patterns.(2)The concentration and composition of NACs in atmospheric particulates in urban Beijing during 2017-2018 also showed seasonal and diurnal differences.The mean concentration of NACs were almost equal in spring(8.68±6.73 ng m-3)and summer(8.80 ±7.08 ng m-3),while the values in autumn(32.29 ± 45.8 1ng m-3)and winter(46.65±38.60 ng m-3)were comparable.Among them,4-nitrophenol and 4-nitrocatechol were the main NACs species in spring,while the most abundant were 4-nitroguaiacol and 2,4-dinitrophenol in summer.In autumn and winter,the dominant species were 4-nitroguaiacol and 5-nitroguaiacol.Similarly,distinct diurnal variations of nocturnal levels higher than daytime levels were shown for NACs.(3)The results of health risk assessment showed that the average TEQBaP of PAHs and NPAHs in atmospheric particulate matter in Beijing during spring,autumn and winter in 20172018 exceeded the standard recommended by WHO(1 ng m-3),and the ILCR value in each season also exceeded the acceptable level recommended by the US Environmental Protection Agency(10E-6).indicating a potential health risk to residents,especially in winter.(4)Correlation analysis,ratio method and PMF analysis showed that during the 2017-2018 observation period in Beijing urban area,traffic sources contributed to the three types of ACs,while biomass combustion and coal burning were the most important sources in autumn and winter.Atmospheric secondary reaction is another source of NPAHs and NACs,especially in summer.The results of PMF model show that the contribution of other sources or secondary generation,coal burning,traffic and biomass burning to PAHs in the whole year were 7.9%,59.8%,19.2%and 13.1%,respectively,and the contribution to NPAHs was 40.6%,21.0%,9.3%and 29.1%.The contribution to NACs was 16.8%,16.9%,17.2%and 49.1%.(5)NO2 and RH could affect the secondary formation of NPAHs,NACs and NO3-.During the 2017-2018 observation period,When NO2<60 ppb and RH<60%,the heterogeneous reactions of NPAHs were significantly promoted.While NO2<60 ppb and RH<40%,it can significantly promote the heterogeneous reactions of NACs,especially the formation of nitrophenol and nitrocatechol.When the NO2>40 ppb and RH<60%,it may promote the conversion of the products mainly NO3-to NPAHs.However,when NO>30 ppb and RH<40%,it may promote the conversion of the products mainly NO3-to NACs.ACs are important components of organic aerosols.The accumulation of their concentration in the atmosphere is one of the important reasons for the occurrence of ambient air haze pollution,and it will bring potential health risks to human beings.Under the complex primary emissions and secondary formation sources,the pollution status is also different.In this paper,the pollution characteristics,sources and health risks of PAHs,NPAHs and NACs in atmospheric particulate matter in urban Beijing during 2017-2018 were preliminarily analyzed.The research results can provide basic data for understanding the atmospheric environmental behavior and health risks of ACs,and provide theoretical basis for the prevention and control of atmospheric ACs pollution. |
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