Observation Based Study Of VOCs And Their Influence Of On Ozone And Secondary Organic Aerosol Formation In The Western YRD Region,China

Volatile organic compounds(VOCs),acting as the 'fuel' of atmospheric oxidation processes,are key precursors for the production of ozone(O3)and secondary organic aerosol(SOA).Based on the measurement of trace gases,VOCs and highly oxygenated moleculers(HOMs),aerosol composition,aerosol lidar,tethered balloon measurements at SORPES(the Station for Observing Regional Processes of the Earth System)and numberical simulation such as LPDM(Lagrangian particle dispersion model),WRF-Chem and chemical box model,the characteristics of VOCs and their influence on O3 and SOA formation were studied in this paper.The two-year continuous observation of VOCs at the SORPES station showed that the sources of OVOCs in the suburban stations are complex,as both primary emission from anthropogenic sources and photochemical secondary production have significant effects on the concentrations of OVOCs.Methanol,formic acid and acetic acid were of the highest concentrations,with average concentrations of 8.48 ppb,2.81 ppb and 3.93 ppb,respectively.The variation characteristics of isoprene concentration showed obvious seasonal differences.The concentration of isoprene in summer was dominated by biogenic emissions,and the highest concentration in daytime was 6.73 ppb.In winter,the main source of isoprene was anthropogenic,with its variation well correlated with toluene and its concentration only one tenth of that in summer.Aromatic hydrocarbons,primary anthropogenic VOCs,were observed to have higher concentration during the night and showed less seasonal differences.Toluene was of the highest concentration,with an average annual concentration of 0.71 ppb.Isoprene oxidation contributed significantly to 03 formation during summer.The estimated contribution from isoprene first generation oxidation was about 10-12%of O3 concentration during the measurement period of 2018 summer.The observed formaldehyde showed a good correlation with MVK and MACR(main oxidation production of isoprene oxidation).Considering the contribution of formaldehyde and MVK and MACR oxidation,the contribution of isoprene oxidation to O3 in this region may exceed 20%in summer.The contribution of VOCs to O3 generation during National Day holidays was estimated by using the chemical box model based on a simplified MCM chemical mechanism.The results showed that the concentration of VOCs from transportation sources such as alkanes and alkenes increased dramatically and their contribution to O3 generation efficiency also increased synchronously.Meanwhile,transport processes are also an important factor affecting O3 concentration.In this study,the effects of vertical mixing of residual layer and long-distance transport of biomass burning air mass on O3 concentration were analyzed by integrating numerical models and comprehensive observations.The results showed that the contribution of the vertical mixing of residual layer to the 03 growth rate was 30 ppb/hr in the morning,while long-distance transport of biomass burning air masses can lead to an increase in O3 concentration by more than 40 ppb in the downstream areas..Due to the high atmospheric background concentration of nitrogen oxides and strong atmospheric oxidation capacity in China,multi-step oxidation and NO termination reactions dominate the atmospheric chemical reactions,leading to the formation of various highly functionalized organic nitrates.A large number of highly functionalized molecules with the different number of carbon atoms and with the same extend of saturation,same number of oxygen atoms and nitrogen atoms could be observed in the urban air.The PMF results further indicated that these molecules with their similar variation characteristics may be produced by different precursors through the same chemical pathway,reflecting the interaction of source complxity of the urban atmosphere and atmospheric chemical processes.In the Yangtze River Delta region where the interaction of biogenic and anthropogenic sources is strong,more than 85%of the highly functionalized molecules produced by isoprene oxidation in summer were functionalized organic nitrates.The volatility analysis of these molecules showed that more than 71.8%of the functionalized molecules were semi-volatile organic compounds,important precursors of SOA.These moleculers could contribute 7-17%of the organic aerosol mass concentration thorough gas/particle partitioning.