Effects Of Environmental Factors On C₄H₆O₂-NO₂ Photooxidation Formation SOA

Secondary organic aerosols（SOA）are mainly generated by the photochemical reactions between volatile organic compounds（VOCs）and nitrogen oxides（NO_x）,which can cause serious air pollution.SOA generation is affected by a variety of environmental factors,and analyzing the mechanism or regular pattern of such effects is a prerequisite for SOA prevention and control.In this study,vinyl acetate（C₄H₆O₂）and NO₂as the object to explore the effects of light,initial concentration of reactants,relative humidity,seed aerosols and other environmental factors on the formation of SOA,and preliminarily speculated the reaction mechanism of C₄H₆O₂-NO₂photooxidation to generate SOA,in order to provide a reference for experimental data for subsequent work.In this study,self-made smog chamber system as the experimental tool,and the experimental results showed good repeatability with little effects on background gas and wall loss.Studies have found that prolonged light time and increased light intensity under experimental conditions can promote SOA generation.High[C₄H₆O₂]₀increases the maximum SOA number concentration and reduces the potential for SOA generation.Increase[NO₂]₀will simultaneously reduce the maximum SOA number concentration and the SOA generation potential.[C₄H₆O₂]₀/[NO₂]₀and the SOA number the maximum concentration is linearly related.Relative humidity and SOA generation potential may conform to Gaussian distribution.The effect of three seed aerosols on the generation of SOA changed from promotion to hindrance over time,and the order of strength was:（NH₄）₂SO₄>NH₄NO₃>Ca Cl₂,and the increase of concentration would increase the hindrance effect.There was no necessary connection between NO₂and relative humidity on the process of SOA generation and the initial light conditions.Under different experimental conditions,the effects on free radicals are different.It was[NO₂]₀that restricts the potential of SOA generation by[C₄H₆O₂]₀/[NO₂]₀,and the effect of low concentration of NO₂on·OH concentration is more obvious.Relative humidity does not changed the concentration of NO₂,but the two can influence the changed of sulfate formation and·OH concentration.The order of the effect of the three environmental factors on the generation of SOA was:light intensity>initial concentration ratio of reactants>relative humidity.The humidity and p H of Ca Cl₂seed aerosol are important factor affect the generation of SOA.Excessive humidity,too low humidity,or acid-base overexposure and over-acid will significantly inhibit the generation of SOA.