Chamber Simulation Study On Secondary Organic Aerosols Formation From Typical Oxygenated Volatile Organic Compounds In The Atmosphere

Oxygenated volatile organic compounds(OVOCs)are an important part of volatile organic compounds and play an important role in atmospheric chemical processes.These compounds that emit into the atmosphere can participate in a series of atmospheric chemical reactions.OVOCs in the atmosphere react with the main oxidants,such as,OH radicals,Cl atoms,NO3 radicals and O3,which will produce low-volatile products that can be distributed to the particles phase.Therefore,the reaction processes have an important impact on the formation of secondary organic aerosol(SOA).SOA can change the atmospheric radiation balance by absorbing and scattering solar radiation.SOA can also act as cloud condensation nuclei,which in turn affect climate change by changing the nature of clouds.In addition,the production of SOA in the atmosphere can be affected by environmental factors.With the widespread application of unsaturated acetates in industrial production,the emissions in the atmosphere have gradually increased.In addition,the oxidation of isoprene and methacrolein and methyl vinyl ketone,two oxidation intermediates of isoprene,will produce a lot of methylglyoxal.Therefore,in this study,the reaction rate constants of these typical OVOCs allyl acetate,isopropenyl acetate and 2-methyl-2-propenyl acetate with the four oxidants OH radicals,Cl atoms,NO3 radicals and O3 were measured by using relative rate method and absolute rate method in the Teflon reactor.The reaction mechanism was proposed according the detected products.Furthermore,the effects of several environmental factors on the SOA formation from oxidation of AA and methylglyoxal(MG)were also explored.The specific conclusions are as follows:(1)The rate constants of three types of unsaturated esters were measured using absolute and relative rate methods:allyl acetate,isopropenyl acetate and 2-methyl-2-propenyl acetate reaction rate constants with OH radicals,Cl atoms,NO3 radicals and O3.The atmosphere lifetime of the three substances were obtained from the rate constants.It was found that the reaction with OH radicals is the major loss process during the daytime,while the reaction with NO3 radicals is the main process at night.Based on the detected reaction products,the reaction mechanism were proposed,and the main reaction pathway was found to be the addition of oxidants to the C=C bond The main products obtained by the reaction are mult-functional substances,which contribute greatly to the formation of particle.(2)The effects of SO2 and NOx on the SOA formation in the reaction system of methylglyoxal and OH radicals was investigated in the Teflon chamber.The SOA yield,particle mass concentration,particle number concentration,and particle diameter increased with SO2 concentration increasing.Compared with the experiments without NOx and SO2,the SOA yield decreased under high NOx([VOC]0/[NOx]0<3.0),and the SOA yield increased with NOx concentration increasing under low NOx([VOC]0/[NOx]0>3.0)in the presence of SO2.Similarly,the particle number concentration and mass concentration also decrease under high NOx condition,and the particle diameter also decrease.While the change trend of particle mass concentration,particle number concentration,and particle diameter similar with the change trend of SOA yield under low NOx conidtion.The reaction mechanism was proposed according to the detected products,and it can be seen that the reaction pathways are the H atom ion and hydration.Sulfate and nitrate were formed in the present of NOx and SO2 from the infrared spectrum.Wherase,the position of the infrared absorption peaks was affected by the different experimental conditions.(3)The effects of different VOC/NOx ratios and relative humidity on the SOA formation of allyl acetate photooxidation were investigated using the Teflon chamber.Under low NOx conditions([VOC]0/[NOx]0>3.0),the SOA yield increased with increasing NOx concentration,while under high NOx conditions([VOC]0/[NOx]0<3.0),the SOA yield decreased with increasing NOx concentration.One-product model was used to simulate SOA yield dependence on aerosol mass concemtration and found suitable for reproducing the experimental data,which indicated that semi-volatile organic compounds were the major products in the particle phase.The concentration of O3 was different at different levels of NOx during the experiment.The concentration of O3 produced under low NOx conditions was higher than that under high NOx conditions,which indicates that high NOx concentration will suppresse the formation of O3.The change trend of particle number concentration depends on AA/NOx ratio,and the particle number concentration usually higher under low NOx conditions than under high NOx conditions.The change trend of particle mass concentration and particle diameter were similar with the change trends of particle number concentration,which are generally higher under low NOx conditions than under high NOx conditions.CH3COOCH2CH(O)CH2,CH3COOCH2COOH,CH3COOCHO and acetic acid were the main products of AA photooxidation.In addition,the effects of low relative humidity(14-16%),medium relative humidity(30-31%),and high relative humidity(68-70%)on the SOA formation from the oxidation of AA were investigated.The experimental results show that the particle mass concentration and the particle diameter decrease with the increase of relative humidity.The particle number concentration does not change significantly with the relative humidity.In addition,it can be seen from the infrared spectrum that the change of the relative humidity does not affect the functional group types in the particles.The oxidation process of oxygenated volatile organic compounds in the atmosphere can be better understood through the investigation of the gas phase kinetics of typical oxygenated volatile organic compounds and the influence of environmental factors on the formation of secondary organic aerosols of typical oxygenated volatile organic compounds.This study provides laboratory data support for the contribution of atmospheric chemistry of oxygenated volatile organic compounds to the formation of secondary organic aerosols,and reveals the contribution of atmospheric oxidation of oxygenated volatile organic compounds to the formation of atmospheric pollutants.Furthermore,it provides some theoretical guidance for air pollution control.