Characteristics Of Polycyclic Aromatic Hydrocarbons?PAHs?and Their Derivatives?NPAHs,OPAHs?in PM_2.5Emitted From Motor Vehicles

Atmospheric particulate matter is an important pollutant that causes climate change and changes in air quality,and it is harmful to human health.Compared with coarse particles,fine particles(PM2.5)have a smaller particle size and a larger specific surface area.Therefore,PM2.5 can stay in the atmosphere for a longer time and are more likely to adsorb harmful substances in the atmosphere.Organic components are an important part of PM2.5,which contributes 20 to 90%of the PM2.5 mass concentration.Polycyclic aromatic hydrocarbons(PAHs)and their derivatives(NPAHs and OPAHs),as an important organic component in PM2.5,have attracted more and more attention due to their higher toxicity.In recent years,with the rapid growth of the number of motor vehicles,motor vehicle emissions have become one of the important sources of PAHs,NPAHs and OPAHs in PM2.5.The study of PM2.5 emissions from motor vehicles can make the air pollution data in a certain area more comprehensive,and provide scientific reference for prevention and control measures to reduce pollutants emitted by motor vehicles.However,there are few studies on PAHs.NPAHs and OPAHs in PM2.5 emitted from motor vehicles.Therefore,further studies on the pollution characteristics of PAHs,NPAHs and OPAHs in PM2.5 emitted by motor vehicles has great academic and application value.In this study,the vehicle drum(bench)experiment,tunnel experiment,and road experiment were used to collect PM2.5 emitted from motor vehicles,and the PAHs,NPAHs and OPAHs in PM2.5 were analyzed.The concentration level and molecular composition of aromatic hydrocarbons were analyzed.The emission factors of PAHs,NPAHs and OPAHs in PM2.5 emitted by motor vehicles were calculated,and their health risks were estimated.Based on the experimental data obtained from the vehicle drum experiment,this research systematically grasped the emission levels and change characteristics of PAHs and NPAHs in PM2.5 emitted by gasoline vehicles.Under the China I to China V emission standards,the average emission factors of PAHs and NPAHs in PM2.5 emitted by gasoline vehicles decrease with the increase of emission standards.The emission factors of NPAHs are 2-3 orders of magnitude lower than their corresponding PAHs.Under different emission standards,BghiP,DahA and BkF are the most abundant PAHs in PM2.5 emitted from gasoline vehicles,BaP and 6N-CHR are the dominant components in NPAHs;the sum of 4-rings,5-rings,and 6-rings PAHs contributed more than 95%of the total PAHs.The change in mileage of gasoline vehicles may have a greater impact on 4-ring PAHs.Under different emission standards and mileage,there was no significant difference in the proportion of NPAHs by number of rings.Based on the observation and analysis of PAHs and NPAHs in PM2.5 emitted by gasoline vehicles equipped with different types of engines,it was found that the emission factors of PAHs and NPAHs in PM2.5 emitted by the port injection(PFI)engines were larger than that in direct-injection(DI)engines under different cumulative mileage.The engine type has little effect on the distribution of PAHs and NPAHs in PM2.5 emited from gasoline vehicles.Compared with PFI gasoline vehicles,DI gasoline vehicles are more conducive to the accumulation of high-rings NPAHs in PM2.5.In addition,the study also found that the emission of PAHs and NPAHs in PM2.5 emitted from gasoline vehicles has a small correlation with CO emissions,and the total amount of PAHs has a strong positive correlation with HC emissions.However,the correlation between the total amount of PAHs and HC was weak,indicating that gasoline vehicle engines may have similar conversion efficiency to HC and PAHs;The correlation coefficients between individual NPAHs and their corresponding parent PAHs were significantly different.4-rings NPAHs(1N-PYR,2-PYR,7N-BaA and 6N-CHR)and their parent PAHs(PYR,BaA and CHR)had highly correlations,while 5-rings NPAH(6N-BaP)and its parent PAH(BaP)showed no correlation.By calculating the equivalent carcinogenic equivalent concentration(TEQ)of PAHs and NPAHs in PM2.5 emitted by gasoline vehicles,it was found that the TEQs of total PAHs and NPAHs from China 3,China 4 and China 5 vehicles were significantly reduced compared to that from China 1 and China 2 vehicles,which may be related to exhaust technology improvements.By carrying out observation experiments in the Yangkou Tunnel of Qingdao,this study obtained the concentration levels and molecular composition of PAHs,NPAHs and OPAHs in PM2.5 in the tunnel,and combined with the characteristic ratio the principal component analysis(PCA)to explore their main sources,and finally the emission factors of PAHs,NPAHs,and OPAHs in PM2.5 in the tunnel were quantitatively estimated.The results showed that FLT and PYR are the most abundant PAHs,1N-PYR and 2N-PYR are the dominant NPAHs,and 9-FO and 9,10-ANQ has the highest concentrations of OPAHs.The characteristic ratio and PCA analysis results showed that the PAHs and NPAHs in PM2.5 in the tunnel were mainly derived from exhaust emissions from gasoline and diesel vehicles,rather than exhaust emission sources(such as road dust,brake pipes,asphalt,tire wear,etc.)also contribute to the PAHs and NPAHs in PM2.5 in the tunnel.Therefore,it is also necessary to formulate appropriate regulations to regulate non-exhaust gas emissions and take appropriate control measures.The emission factors of total PAHs,total NPAHs and total OPAHs in PM2.5 in the tunnel were 60.98,9.02,and 8.47 ?g veh-1 km-1,respectively.The emission factor of PAHs with high ring numbers(4-6 rings)was significantly greater than that of PAHs with low ring numbers(2-3 rings).Among all the measured NPAHs,1N-PYR has the highest emission factor;9-FO and 9,10-ANQ were the two OPAHs with the highest emission factors.Using road experiments,this study explored the pollution characteristics of PAHs,NPAHs and OPAHs in PM2.5 emitted by motor vehicles in the actual atmosphere,and obtained the concentration levels and molecular composition of PAHs,NPAHs and OPAHs in urban and suburban roadside sites in Qingdao,and their sources were identified using characteristic ratios and PCA analysis.The life-cycle cancer risk increase(ILCR)was used to assess the risk of exposure to human health in different age groups of PAHs and NPAHs in PM2.5 in the urban and suburban roadsides of Qingdao.The results showed that compared with the heavily polluted inland regions,the pollution of PAHs and their derivatives in Qingdao was lighter.At urban roadside site,FLT and PHE were the dominant components of PAHs in PM2.5,while at suburban road roadside site,FLT and PYR were the most abundant components of PAHs,at urban and suburban roadside sites,9N-ANT and 2+3N-FLA were the most abundant NPAHs;9-FO,1-NALD and 9,10-ANQ were the three main components of the OPAHs.In urban and suburban roadside sites,4-rings PAHs were the dominant PAHs,and 4-rings NPAHs were the dominant components of the observed NPAHs.In urban areas,the morning and evening peaks were the two periods when PAHs and nitro polycyclic aromatic hydrocarbons have the highest concentration,which is consistent with the time period of heavy traffic in urban areas.In the suburbs,the highest PAHs and NPAHs appeared during the early peak hours,and the second highest values occurred at night.Unlike the daily variation trend of PAHs andNPAHs,there is no clear trend of the peak value of the concentration of OPAHs.However,in urban and suburban areas,the lowest values of PAHs appeared at noon.The characteristic ratio and PCA analysis results showed that the PAHs in the PM2.5 of the urban roadside site were mainly derived from coal and oil combustion and vehicle exhaust emissions,the PAHs in the PM2.5 of the suburban roadside site were mainly derived from coal and petroleum combustion sources,motor vehicle emissions sources,and biomass combustion sources.NPAHs and OPAHs in PM2.5 in urban areas mainly come from motor vehicle emissions and solid fuel emissions,NPAHs and OPAHs in PM2.5 in urban areas mainly come from vehicle emissions,solid fuel combustion,biomass combustion,and secondary production.In addition,this study also found that the toxicity of NPAHs in PM2.5 in urban and suburban roadside sites during heavy traffic periods was higher than that in idle periods,the emission of motor vehicles was conducive to increase in the toxicity of NPAHs in PM2.5.In this study,the concentration levels,molecular composition,emission factors and health risks of PAHs,NPAHs and OPAHs in PM2.5 emitted by motor vehicles were analyzed in depth.It provides data support for the study of motor vehicle emission pollution in China,and provides a theoretical basis for the development of motor vehicle emission pollution control measures in China.