| As a class of organic pollutants with high carcinogenicity,PAHs is widely distributed in the environment and has attracted worldwide attention.Gaseous PAHs in atmospheric environment can enter the human circulation system through respiratory exposure and cause irreparable health damage to the body.The Bohai Sea region is characterized by high population density,rapid economic development and high PAHs emissions.The ecological environment along the Bohai Sea region is relatively sensitive,which makes the atmospheric PAHs pollution in the Bohai Sea region in a severe situation.A large number of studies have shown that coal combustion and motor vehicle exhaust are the main sources of atmospheric PAHs in the Bohai Sea region,as well as an important emission source of PM2.5,the primary atmospheric pollutant.In recent years,aiming at the serious air pollution problem,China has implemented a series of prevention and control measures mainly to control PM2.5 to effectively reduce the emission of air pollutants.Due to the homology of PAHs and PM2.5,air pollution control actions will have a synergistic control effect on PAHs emissions.It is of great significance to pay attention to the pollution status,sources and potential health risks of atmospheric PAHs in the Bohai Sea region under the background of air pollution control.Due to the impact of COVID-19 control in 2019,anthropogenic activities were greatly restricted,resulting in a significant decrease in the emissions of various pollutants.Therefore,it is of certain practical significance to study the response changes of atmospheric PAHs in Bohai Sea region during this period.In this study,twelve atmospheric monitoring stations were deployed around Bohai Sea,and long-term observations of atmospheric PAHs were made by using atmospheric passive samplers from June 2014 to August 2020.The 16 PAHs listed by US Environmental Protection Agency（USEPA）were detected by gas chromatography-mass spectrometry.Based on the analysis of atmospheric PAHs concentration levels and pollution characteristics,PCA and PMF models were used to analyze the sources of PAHs,and the temporal and spatial variation of PAHs concentration and the difference of source contribution under the background of air pollution control were discussed.The Increased Lifetime Cancer Risk（ILCR）and Population Attribution Fraction（PAF）were used to assess the health risks of atmospheric PAHs,and estimated the direct medical costs of lung cancer caused by respiratory exposure to PAHs.The changes of atmospheric PAHs in response to COVID-19 control around Bohai Sea in terms of concentration composition and health risk were analyzed using monitoring data of different periods,and the specific research results are as follows.（1）From June 2014 to May 2019（five cycle years）,the concentration of 15 PAHs（16 PAHs excluding naphthalene）ranged from 51.4 to 63.6 ng/m3,with an average concentration of 56.8±4.7 ng/m3.The low-ring（3-ring）PAHs contributed the most,and the range was 54.4 to 63.2%.Phe was the dominant species among 15 PAHs,and DahA had the lowest concentration.The concentration of PAHs showed a decreasing trend year by year,decreasing by 17.5%in five years,among which the concentration of the high-ring（5-ring and 6-ring）PAHs decreased by the most,74.8%.The seasonal concentration of PAHs was winter>autumn>spring>summer,the spatial distribution was high in the north and low in the south.（2）The study found that PM2.5 and PAHs concentration around Bohai Sea during the same period were significantly correlated,and the significant inter-annual difference of PAHs concentration was corresponding to the implementation process of air pollution prevention and control,that was,the control of different emission sources in different periods changed the emission of sub-ring PAHs.Air pollution control,mainly PM2.5 control,had a synergistic control effect on PAHs,and in Tianjin,where source emission control was stricter,the concentration of PAHs decreased the most,which is51.7%.（3）The analysis results showed that the sources of atmospheric PAHs around Bohai Sea were coal combustion emissions（49.6%）,biomass combustion（22.0%）,industrial processes（10.8%）,gasoline emissions（9.4%）and diesel emissions（8.2%）,and coal burning emissions was the main sources of annual PAHs in the Bohai Sea region.As two important sources,traffic emissions and coal emissions have obvious inter-annual variation differences in regions with different control intensity.In the whole Bohai Sea region,the contribution of motor vehicle emissions to PAHs decreased by 22.7%,and the contribution of coal burning increased by 6.7%,while in Tianjin,the contribution of motor vehicle emissions increased by 6.7%,and the contribution of coal burning decreased by 13.2%.（4）The health risk assessment of PAHs indicated that the ILCR due to exposure to atmospheric PAHs decreased by 74.3%in the Bohai Sea region between June 2014and May 2019.The estimated results of the direct medical cost of lung cancer showed that compared with the non-implementation of air pollution control,the direct medical cost of lung cancer caused by PAHs respiratory exposure in the Bohai Sea region after the actual implementation of air pollution control is reduced by approximately 64.4million yuan,which accounted for 0.1%of China’s estimated direct expenditure on lung cancer in 2017.The direct medical costs of lung cancer caused by PAHs exposure decreased by 45.8%in the Bohai Sea region and 52.9%in Tianjin.（5）The comparative analysis of atmospheric PAHs concentration and health risks in the Bohai Sea region before and after COVID-19 in 2019 showed that the reduction of human activities during the epidemic control period led to a 57.3%decrease in atmospheric PAHs concentration,which was mainly contributed by the decrease of low-ring PAHs.The health risk was reduced by 30.3%,mainly associated with a reduction in the concentration of high-ring PAHs. |
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