Observation-based Research On Atmospheric Carbonyl Compounds In Typical Areas Of Shandong Province

Carbonyl compounds are an important type of oxygenated volatile organic compounds（OVOCs）,which play an important role in atmospheric chemical processes,especially in the formation of ozone and secondary organic aerosols（SOA）,and influence human health as well.This article selected Shandong Province,which has a developed economy,a large population,and a large number of industries,to study atmospheric carbonyl compounds in its typical areas.Qingdao（coastal suburbs site）,Linyi（South of Shandong urban site）,Binzhou（Yellow River Delta urban site）,Tai’an（hilly city urban site）and Ji’nan（provincial capital city urban site）were selected as typical areas to conduct field observations respectively,and data analysis methods,such as multiple linear regression analysis,correlation analysis,backward trajectory analysis,and MCM box model were used to investigate the carbonyl compounds pollution characteristics,temporal and spatial variations and distributions,source and sink,environmental impacts and health risk assessments.In this study,field observations were conducted in spring,summer,autumn,and winter in Qingdao from December 2019 to November 2020.Field observations in other typical areas were all conducted in summer from June to August 2020.In total there were 8 observation periods of atmospheric carbonyl compounds.A total of 15 aldehydes and ketones were determined.Formaldehyde,acetone and acetaldehyde had the highest concentrations,and these three carbonyls accounted for 53.69%～84.93%of the total carbonyls.The atmospheric carbonyl concentrations in Qingdao site showed seasonal characteristics of spring（20.84μg/m³）>autumn（20.15μg/m³）>winter（17.58μg/m³）>summer（9.13μg/m³）;the daily variations of carbonyls in different season were characterized by a bimodal mode,with peaks appearing at 8:00-12:00 and 16:00-20:00,respectively,which were significantly affected by morning traffic peak and evening traffic peak.There were also afternoon peaks in summer and autumn;in different seasons,daytime concentrations of carbonyls were all higher than nighttime.The observations in Linyi and Binzhou sites showed obvious morning peaks,while there were large differences in daily variations of carbonyls at Tai’an and other sites,and there showed nighttime peaks,which may be affected by regional transport.Comparing the carbonyl concentrations at Binzhou site in 2018 and 2020,and at Tai’an site in 2019 and 2020,it was all found that there were no significant variations;the carbonyl concentrations decreased by42.27%to 78.32%during the rainfall process,which indicated that rainfall is an important sink for atmospheric carbonyls.The characteristics of carbonyl concentrations in typical areas of Shandong Province showed that the concentrations at Linyi and Tai’an sites in the south Shandong were higher than those at Jinan and Binzhou sites in the north Shandong,the concentrations at Qingdao coastal site were lower than that at inland site at the same latitude,and the concentrations in typical areas in Shandong were lower than that at cities in the south China.The value of formaldehyde to acetaldehyde ratio（C₁/C₂）in Qingdao was between 1-3,which indicated the combined influence of anthropogenic and natural sources;C₁/C₂ratios in Linyi,Tai’an,Jinan,and Binzhou were between 1-2,which showed the carbonyl characteristics of urban areas.The value of acetaldehyde to propionaldehyde ratio（C₂/C₃）in the observations was from 1.81 to 9.95,which consistent with the results of other domestic research sites.Formaldehyde,acetaldehyde,propionaldehyde and butyraldehyde in Qingdao in winter were contributed by primary sources such as vehicle exhaust emissions and fuel combustion,and the secondary photochemical sources of formaldehyde and acetaldehyde contributed the most in seasons with strong sunlight;the background sources in Tai’an contributed the most to carbonyls;In Linyi,Jinan and Binzhou,the primary source contributed the most,and the secondary source also contributed a certain proportion.In all observations,the acetone with weakest chemical reactivity mainly came from background sources.The correlations between carbonyl species in different seasons in Qingdao in winter were quite different,which showed the sources and sinks of carbonyl compounds in the four seasons were different and diverse;formaldehyde and acetaldehyde in four cities all had strong correlations,and the correlations between acetone,propionaldehyde,butyraldehyde and NO₂were very strong in Tai’an,however the correlations in other cities were relatively weak.Air mass trajectories in different seasons were different,leading to different transport sources in Qingdao,while regional transports in other cities in summer were affected by the summer monsoon mainly coming from the south.The production pathways of HCHO and CH₃CHO in Linyi and Qingdao were all controlled by the reaction of RO+O₂.The consumption pathway of HCHO was mainly photolysis and its reaction with OH radicals,while the consumption pathway of CH₃CHO was mainly its reaction with OH radicals.HCHO and CH₃CHO all showed as net production,which indicated in-situ photochemical processes could promote their formation.Among the contributions to OH radical loss rate(L_OH)and Ozone Formation Potential（OFP）,formaldehyde and acetaldehyde were dominant species,and propionaldehyde and butyraldehyde also had significant contributions.Among VOCs which were monitored simultaneously in certain periods,alkenes contributed the most to OFP,followed by aromatic hydrocarbons and alkanes.Among the contributions to SOA,benzaldehyde contributed the most to SOA,accounting for 59.00%to 95.11%,while other carbonyl species contribute less.In different seasons,the SOAp ranking is late spring>autumn>winter>summer,and Linyi site had the largest contribution to SOA among all observation sites.Human health risk assessment showed that among typical areas in Shandong,except for Qingdao in late spring and summer,there existed a certain risk of cancer in other seasons and in other cities.Comparing different cities,it was found that Qingdao had a much lower risk.In this study,we obtained the concentration levels,pollution characteristics,temporal and spatial variations of atmospheric carbonyl compounds in the four urban sites in four cities（Linyi,Tai’an,Jinan,and Binzhou）,and in the coastal suburb site in Qingdao,their sources,atmospheric photochemical activity and human health risks were investigated,which were of importance to understand the atmospheric carbonyl characteristics in Shandong Province.The results will help policy makers at government agencies of environmental protection to formulate relevant measures to reduce atmospheric photochemical pollution in specific areas in Shandong Province or in China.