Sources Apportionment Of Atmospheric Carbonyls And Evaluation Of Their Contribution To Ground-level Ozone

Promoting the synergistic control of fine particulate matter(PM2.5)and ozone(O3)is an important part of China’s 14th Five-Year Plan on constructing ecological civilization.Atmospheric carbonyls are an important part of oxygenated volatile organic compounds(OVOCs),which are key precursors and intermediates for the formation of PM2.5 and O3 in ambient air;some carbonyls with low molecular weight have direct negative impacts on human health,with potential hazards such as sensitization,carcinogenesis and mutagenesis.The sources of atmospheric carbonyls are complex,including primary emission and secondary formation;the accurate analysis of carbonyls sources is the current hot topic and difficulty in the research of VOCs source analysis.The study of pollution characteristics and potential sources of carbonyls can provide support for the synergistic control of PM2.5 and O3.This study integrates field experiments,laboratory analysis and model simulations to construct a quantitative analysis method for primary emissions and secondary formation of atmospheric carbonyls.The applications were carried out in the Beijing urban area,Yulin urban area and Mount Tai in China to compare and analyze the differences in pollution characteristics and sources of atmospheric carbonyls with different climatic conditions,energy structures and air pollution.Moreover,this study explores the contribution of carbonyls to O3 formation.This study established a sensitive simultaneous detection approach to determine 30 atmospheric mono-,di-,oxygen-containing and heterocyclic carbonyls by DNPHHPLC/APCI-MS based on commercial standard derivatives.The results showed that the detection limit of 30 carbonyls ranged from 4.77 to 49.32 ng/m3 with an ambient air sampling volume of 96 L.Compared with the traditional method,the number of species determined in this study increased nearly two times,while the linear ranges and limits of detection were both improved by an order of magnitude.In this study,different samplers and suitable sampling conditions were used to carry out carbonyls sampling experiments in ambient air and stationary pollution source,and the concentrations of atmospheric carbonyls were obtained by the DNPH-HPLC/APCI-MS method.Field observation experiments showed significant differences in the concentrations of carbonyls in various regions of China.The total concentrations of 30 carbonyls(Σ30OVOCs)for Beijing,Yulin and Mount Tai are in descending order,14.86±7.82 ppbv,11.97±8.03 ppbv and 8.93±3.61 ppbv,respectively.It is commonly accepted that formaldehyde,acetaldehyde and acetone are the dominant species in different areas,and their total concentrations account for 57-69%of Σ30OVOCs in Beijing,Yulin and Mount Tai.Comparing the historical monitoring data of the Beijing urban area and Mount Tai,this study found that the concentrations of formaldehyde(-0.61±0.15 ppbv/year,-7%),acetaldehyde(-0.43±0.11 ppbv/year,-10%),acetone(-0.40±0.05 ppbv/year,-6%)in Beijing and acetaldehyde(0.13±0.02 ppbv/year,-9%),acetone(-0.23±0.07 ppbv/year,-9%)at Mount Tai decreased significantly in the past 15 years,and the decreasing trends were more significant in the period of implementing clean air action in China(2013-2021).Comparing the concentrations of formaldehyde,acetaldehyde and acetone in different regions of China and the United States,it was found that the atmospheric formaldehyde and acetaldehyde concentrations in China are significantly higher than those in the United States.The concentrations of formaldehyde,acetaldehyde and acetone in the Sichuan Basin were the highest among the four key regions in China(Beijing-Tianjin-Hebei,Yangtze River Delta,Pearl River Delta and Sichuan Basin).The formaldehyde and acetaldehyde concentrations of Mountain site in the Beijing-Tianj in-Hebei region are significantly higher than those in the Pearl River Delta region.This study developed a source apportionment method(Observation-Based Model and Positive Matrix Factorization for Sources Apportionment of Atmospheric Carbonyls,OBMPMF/SAAC method)for typical atmospheric carbonyls based on observational data.First,the primary emission and secondary formation concentrations of carbonyls are distinguished;secondly,combined with VOCs data,the primary source of typical carbonyls is determined;third,the secondary formation and consumption pathways and sensitivity of carbonyls are identified,and the contribution of each source to secondary carbonyls is calculated.Finally,the contributions of different sources to the primary and secondary carbonyls were calculated comprehensively.The feasibility test results of the OBM-PMF/SAAC method show that this method could analyze the primary emission and secondary formation of typical carbonyls.The source analysis method solves the problem that the source of atmospheric carbonyls cannot be accurately identified.The carbonyl sources analyzed by the OBM-PMF/SAAC method showed significant differences in various regions of China.Formaldehyde,acetaldehyde and acetone have primary emission sources and secondary formation sources.The contribution of gasoline vehicle exhaust to formaldehyde is the most prominent(57%),and the contribution of industrial process sources to acetaldehyde and acetone is dominant(27%and 90%,respectively)in the Beijing urban area.Coal to olefins in the Yulin urban area contributed most prominently to formaldehyde and acetaldehyde,and chemical volatilization contributed most to acetone(30%,56%and 85%,respectively).The sources of carbonyls at Mount Tai are more complex,with chemical volatilization and vehicle exhaust contributing to the largest percentage of formaldehyde and acetaldehyde(52%and 26%),respectively.Glyoxal and methylglyoxal were dominated by secondary sources,with plant sources contributing significantly to glyoxal and methylglyoxal in Beijing,Yulin and Mount Tai.The sensitive precursors of different carbonyls have some commonality at the above three sites;secondary formation of formaldehyde and acetaldehyde are more sensitive to alkenes,while acetone is more sensitive to alkanes,and glyoxal and methylglyoxal are most sensitive to aromatics.Carbonyls in the urban area of Beijing and Yulin are dominated by local emission and in-situ formation,while regional transportation is dominated at Mount Tai.The above results indicate that different control actions should be taken for variable carbonyls and sites.O3 formation are in VOCs-limited,mixed-limited and NOx-limited in Beijing,Yulin and Mount Tai,respectively;O3 formation in Beijing is most sensitive to carbonyls and alkenes in anthropogenic VOCs,while Yulin and Mount Tai are alkenes in anthropogenic VOCs and NOx.Few studies concerned the impact of carbonyls on O3 formation sensitivity,while the impact was analyzed in this study.The results show that the maximum hourly O3 formation rate and 24-hour daily accumulation at the above three sites decreased by 12-34%and 12-37%,respectively,when there was no carbonyl chemistry in the model.This study also found that the effects of atmospheric carbonyls on O3 formation were significantly different with the photochemical regime;O3 formations in Beijing and Mount Tai in VOCs-regime and NOxregime,respectively.Thus,emission reduction of carbonyls could significantly decrease O3 concentration in Beijing urban area but slight decrease at Mount Tai,reflecting the difference in O3 pollution control in different O3 formation regimes.The research results can provide theoretical support for atmospheric carbonyl control and help to establish and improve the technical methods for VOCs source analysis;furthermore,the study could provide scientific support for the synergistic control of PM2.5 and O3 in China during the 14th Five-Year Plan period.