| Air pollution poses a potential threat to the global ecological environment and public health.Polycyclic aromatic hydrocarbons(PAHs)are a class of persistent organic pollutants distributed in various environmental media,which are often concentrated in particulate matter and have been widely concerned and studied due to their teratogenic,carcinogenic and mutagenic hazards due to long-distance migration in the environment.In order to investigate the pollution characteristics and health risk of PAHs in the Western Fenwei Plain,PM2.5 samples were collected in Xi’an and a rural area of Baoji during heating period and non-heating period from December 2018 to April 2019,which are selected for comparation from the urban agglomeration of Fenwei Plain.GC-MS was used to determine the mass concentration of 16 kinds of priority controlled PAHs.Under different sampling period and different air quality based on the analysis of PAHs in the PM2.5 pollution characteristics,on the basis of using the characteristic ratio method,principal component analysis(PCA),and positive definite matrices factor analysis(PMF)sources of PAHs,and discusses the possible effect of meteorological conditions on the content of PAHs,finally using the BaP toxicity equivalent method and lifetime cancer risk model(ILCR)exposure to PAHs crowd health risk assessment.The main conclusions are as follows:(1)The average mass concentration of PM2.5 during heating period and non-heating period in western cities of FenWei plain are 140.17±70.57 μg/m3 and 63.65±26.44 μg/m3,respectively,and the average mass concentration of PM2.5 during rural heating period is 215.02±67.63 μg/m3.As a whole,the PM2.5 concentration in the same heating period is much higher than that in the non-heating period,while that in the same sampling period is much higher in the rural areas than in the urban areas.(2)The average mass concentration of PAHs in PM2.5 during heating period and non-heating period in western urban areas of FenWei plain was 111.14±76.77 ng/m3 and 60.81 ±9.35 ng/m3,respectively,and the average mass concentration of PAHs in rural heating period was 375.46±197.78 ng/m3.The spatial and temporal distribution characteristics were basically consistent with PM2.5.In different regions and different sampling periods,the proportion of LMW-PAHs was the lowest,the proportion of HMW-PAHs was the highest in urban heating period and non-heating period,accounting for 49.23%and 55.33%of E PAHs,respectively,and the proportion of MMW-PAHs was the highest in rural heating period,accounting for 65.98%of ∑PAHs.(3)The source analysis of PAHs in PM2.5 in the western cities and rural areas of the FenWei plain shows that coal and biomass fuel combustion and vehicle exhaust are the main emission sources during the heating period in urban areas,and the use of natural gas also contributes to PAHs in PM2.5.During non-heating period,the contribution rate of vehicle exhaust to PAHs was the highest,followed by that of coal and biomass combustion,and the proportion of petroleum was relatively low.In rural heating period,coal and biomass combustion accounted for the highest proportion of PAHs,while the contribution rate of vehicle exhaust was relatively small.(4)The correlation between meteorological factors and PAHs concentration in PM2.5 during the sampling period shows that the temperature has a significant negative correlation with PAHs concentration in heating period,while it has no significant correlation with non-heating period in cities.The correlation between relative humidity and PAHs concentration in non-heating period in urban areas was-0.428,and there was no significant correlation with PAHs content in heating period,while wind speed had no significant correlation with PAHs concentration in each sampling period.There was no significant correlation between air pressure and PAHs concentration in urban areas,but a significant positive correlation with PAHs concentration in rural heating period(R2=0.490).The results of partial correlation analysis show that among various meteorological factors,temperature has a relatively large influence on the concentration of PAHs in PM2.5 during urban heating period,while PAHs is significantly affected by relative humidity in PM2.5 during non-heating period.However,under the background of high emission,PAHs concentration in rural areas is subject to the comprehensive influence of various meteorological conditions,but is not significantly affected by a single meteorological factor.(5)The average mass concentration of PAHs in PM2.5 in urban area is 63.65±15.53 ng/m3,77.24±27.56 ng/m3,89.19±20.21 ng/m3,and 224.10±91.02 ng/m3,respectively,when the air quality is good,mildly polluted,moderately polluted and severely polluted.Under the four weather conditions,the average concentration of PAHs in rural area was 190.58±4.53 ng/m3,222.61 ±80.93 ng/m3,275.13±102.74 ng/m3 and 364.30± 139.04 ng/m3,respectively.Under the same air quality,the PAHs concentration in rural areas was much higher than that in urban areas.The source analysis results show that PAHs sources are different under different air quality in urban areas.PAHs sources are relatively complex when air quality is good,petroleum sources occupy a certain proportion,and liquid fossil fuel combustion sources dominate.In light pollution weather,coal and biomass combustion sources are the main emission sources,followed by transportation sources and a small amount of petroleum sources.In the case of moderate pollution and heavy pollution,the characteristics of pollution sources are similar.Coal,biomass combustion and traffic emission source are the main emission sources of PAHs,but there is no significant emission from petroleum sources.In rural areas,there was no significant difference in PAHs pollution sources in PM2.5 under different pollution conditions.The burning of fuels such as coal and biomass was the main source,and the proportion of vehicle exhaust emission sources was relatively low.(6)The results of health risk analysis showed that only children in the non-heating period in the city had no significant carcinogenic risk,while the risk values of PAHs exposure of different populations in the other sampling periods all exceeded the acceptable level,and there were potential carcinogenic risks.In addition,the carcinogenic risk of different age groups and gender showed the characteristics of the highest exposure risk of adult males,the second highest exposure risk of adult females and the lowest exposure risk of children.The results showed that the carcinogenic risk of PAHs in PM2.5 exposed to different air quality only in urban areas was acceptable when the air quality was good,mildly polluted and moderately polluted,while the carcinogenic risk of all urban and rural groups under the air quality level was higher than the risk threshold.With the same air quality,the risk of cancer among people in rural areas is higher than that in urban areas,and with the aggravation of air pollution,the risk of cancer caused by PAHs exposure of the same population to PM2.5 also increases. |
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