The Pollution Characteristics And Health Risk Assessment Of Atmospheric Carbonyl Compounds In The Beijing-Tianjin-Hebei Region

With the rapid development of China’s economy,the extensive use of fossil fuels has caused serious regional haze and ozone pollution.In recent years,the government has implemented a series of air pollution prevention and control measures,and the overall air quality has improved.However,Field measurement shows that the problem of haze pollution in winter has not been solved in Beijing-Tianjin-Hebei region,but the problem of ozone pollution in spring and summer is increasingly serious.Carbonyl compounds are the important components of volatile organic compounds in the atmosphere,important intermediate products in atmospheric photochemical reactions,and important precursors of active ROx radicals,photochemical oxidants ozone（O₃）and peroxyacetyl nitrate（PAN）in the atmosphere.To explore the influence of carbonyls on ozone pollution in Beijing-Tianjin-Hebei area,a multichannel automatic sampler for carbonyls in the atmosphere was developed.The silica gel column of 4-dinitrophenylhydrazine（DNPH）was used for high frequency derivatization sampling,and the separation and detection were carried out by high performance liquid chromatography.Carbonyls in typical urban area（Station of Research Center for Eco-Environmental Sciences in Beijing）and typical rural area（Station of Rural Environment in Hebei）in Beijing-Tianjin-Hebei region were simultaneously observed from winter 2018 to summer 2019.In this study,the species compositions,concentration levels and temporal and spatial variation characteristics of carbonyl compounds in the atmosphere of typical stations in Beijing-Tianjin-Hebei region were obtained,and the source characteristics,chemical reaction activities of carbonyls and their impacts on the regional atmospheric environment were explored.Experimental results were shown as following:1.Thirteen carbonyl compounds were detected in the atmosphere of Beijing and Hebei rural area,including formaldehyde,acetaldehyde,acetone,propionaldeh yde,acrolein,butyraldehyde,crotonaldehyde,valeraldehyde,isovaleraldehyde,benz aldehyde,methylbenzaldehyde,hexanal and dimethylbenzaldehyde.The concentrati ons of carbonyl compounds in Beijing were the highest in summer（（7.79±3.53）ppb）,followed in spring（（7.43±4.47）ppb）,and the lowest in winter（（5.02±3.07）ppb）.The concentrations of carbonyl compounds were the highest in su mmer（（10.78±4.06）ppb）,the second in winter and spring（（7.28±4.56）ppb and（6.20±3.86）ppb）,and the lowest in autumn（（5.41±3.78）ppb）.Formalde hyde,acetaldehyde and acetone were the main carbonyls in the atmosphere of B eijing and Hebei rural area,accounting for about 85%of the total carbonyl com pounds.During the observation period,carbonyls showed the characteristics of lo w concentration in the daytime and high concentration at night,especially in su mmer in Hebei rural area.Carbonyl compounds in Beijing might be mainly affec ted by local vehicle exhaust emissions and regional industrial sources.However,carbonyls in Hebei rural area was mainly affected by local coal combustion in w inter,while might be greatly affected by vehicle exhaust transported from other places in summer.2.The OH free radical consumption rates(L^OH)of formaldehyde,acetaldehyde,propionaldehyde and butyraldehyde in Beijing and Hebei rural area were more than 70%of the total OH free radical of carbonyl compounds.Taking Beijing summer as an example,the photodegradation rate and the formation rate of peroxyradicals of the carbonyls on the polluted days were significantly higher than those on the clean days,indicating that the photodegradation of carbonyls could provide more free radicals to the atmosphere on the polluted days,which could promote the conversion of NO to NO₂,and thus accelerate the production of ozone.Formaldehyde and acetaldehyde were the dominant species of ozone formation potential（OFP）in the atmosphere,contributing 50%～80%to OFP.L^OH and OFP of carbonyl compounds in Hebei rural area were higher than those in Beijing both in winter and in summer,which might be ascribed to higher concentrations of carbonyl compounds in Hebei rural than in Beijing.In addition,high frequency haze events with dramatically high concentrations of pollutants in Hebei rural area in winter might also be an important reason for higher OFP of carbonyl compounds than in Beijing.3.The carcinogenic risk and non-carcinogenic risk of formaldehyde in Hebei rural area were higher than those in Beijing,and the carcinogenic risk levels of formaldehyde in the two areas both exceeds the risk level given by US EPA,while the non-carcinogenic risk of formaldehyde in the two areas was still within the safe range.Formaldehyde in Hebei rural area and Beijing had the highest carcinogenic and non-carcinogenic risk in summer.