Characteristics Of Polycyclic Aromatic Hydrocarbons And Carbon Isotopes Emitted From Solid Fuel Combustion Sources In Guanzhong Plain

Parent polycyclic aromatic hydrocarbons（p PAHs）and their derivatives oxygenated polycyclic aromatic hydrocarbons（OPAHs）have received extensive attention due to their carcinogenicity,teratogenicity,and mutagenicity.p PAHs are mainly derived from incomplete combustion of anthropogenic or natural sources.Crop straw combustion and household coal combustion are the two major sources of combustion in our country.In order to formulate effective polycyclic aromatic hydrocarbons（PAHs）prevention and control strategies and reduce the potential toxic effects of fine particulate matter(PM_2.5),it becomes particularly important to determine the distribution characteristics and migration mechanisms of PAHs.It is an effective tool to identify the source of PAHs by measuring the stable carbon isotope(δ¹³C)value.Therefore,in this study,a large combustion chamber was used to simulate the combustion of crop straw and household coal in the Guanzhong Plain in our country,and the emitted particulate matter was collected to analyze the p PAHs and OPAHs components.Theδ¹³C value of p PAHs was measured,and theδ¹³C value of p PAHs produced from crop straw combustion sources and household coal combustion sources in Guanzhong Plain was obtained.At the same time,the same analysis was carried out on the environmental samples of Xi’an during the heating period,focusing on the pollution characteristics and health risk assessment of the environmental samples under different air quality.The results showed that among the solid fuel combustion sources,the emission factors of T-p PAHs and T-OPAHs produced by the combustion of corn straw were the highest,and the proportion of four-ring p PAHs was the largest.There was no significant difference in the emission factors of T-p PAHs and T-OPAHs between anthracite lump coal and anthracite briquette.However,the emission of anthracite lump coal is dominated by medium and low ring p PAHs（two-ring,three-ring,four-ring p PAHs）,while the anthracite briquette is dominated by medium and high ring p PAHs（three-ring,four-ring,five-ring p PAHs）.In the environmental samples of Xi’an during the heating period,most of the p PAHs had good correlation,indicating that these compounds came from the same source.Some OPAHs showed significant correlations with most p PAHs,suggesting that these compounds may come from the same source.Some high molecular weight p PAHs and OPAHs were significantly correlated with gaseous pollutants,indicating that secondary aging of p PAHs occurs even in winter.The source apportionment results of environmental samples in Xi’an during the heating period using the diagnostic ratios showed that biomass burning and coal combustion sources and vehicle exhaust emissions were the main sources of p PAHs in PM_2.5 during the sampling period.The mass concentration of individual p PAHs will increase with the increase of pollution level.Among OPAHs,there is also a feature that the concentration of medium and high molecular weight OPAHs increases significantly on polluted days,which should be related to the high concentration of p PAHs and gaseous pollutants on polluted days.The proportions of p PAHs in the fifth and sixth rings increased gradually with the aggravation of pollution,indicating that solid fuel combustion sources and vehicle exhaust emissions contributed more to the heavily polluted days.With the increase of pollution level,the proportion of low molecular weight OPAHs decreases,while the proportion of medium molecular weight OPAHs increases,because the proportion of p PAHs corresponding to low molecular weight OPAHs does not change even reduced with the increase of pollution level.The positive correlation between p PAHs,OPAHs and PM_2.5 also increased with the increase of pollution level within a certain range.In addition,p PAHs were significantly negatively correlated with temperature,air pressure,and wind speed during heavy pollution,while OPAHs were significantly positively correlated with relative humidity（RH）,because an increase in RH might lead to enhanced formation of secondary organic aerosols.Theδ¹³C values of individual p PAHs from solid fuel combustion sources are basically consistent with previous research results.The main emission sources analyzed by theδ¹³C value of the individual p PAHs in the samples were biomass burning,coal combustion,coal processing emissions,and a small amount of vehicle exhaust emissions.Overall,theδ¹³C values of low molecular weight p PAHs（2-3 rings）were more deficient than those of high molecular weight p PAHs（4 rings and above）.From the source analysis results using theδ¹³C value of individual p PAHs,it can be seen that with the increase of T-p PAHs concentration,the range ofδ¹³C value of individual p PAHs will be more deficient,and it is mainly manifested in the middle and high ring p PAHs.That is to say,with the increase of T-p PAHs concentration,the main source of middle and high ring p PAHs will change to the emission source with more deficientδ¹³C-p PAHs value.