Study On The Formation Mechanism And Removal Method Of The Secondary Organic Aerosol

Secondary organic aerosol?SOA?is an important component in atmospheric fine particles(PM_2.5),which has been an issue of enormous interest in recent years because of the possible impacts of SOA on the earth's radiative balance linked to climate change,visibility degradation,and health effects.Study on the formation mechanism and removal method of the SOA has important reference value for atmospheric pollution management.In this study,we investigate the formation mechanism of SOA,find out the dominant factor contributed to haze,in smog chamber,and then we study the removal capacity of the modified molecular sieve for the dominant factor.The main research contents of this article are as follows:?1?Seed particles with different acid-base properties were selected to investigate their influence on secondary aerosol?SA?formation in toluene photo-oxidation with different concentrations of SO₂ and NH₃.The study found that acidic seeds were the dominant factor contributed to haze,and the influence of seed particles on SA formation depended on their acid-base properties and the presented acid or alkaline gases.Due to the acid-catalyzing effect of the oxidation products of SO₂,SA formation increased linearly with SO₂ concentration under NH₃-poor condition.The presence of NH₃ could contribute to SA formation.Meanwhile NH₃ would also eliminate the acid-catalyzing by neutralizing the acid products.The enhancing effect of SO₂ became less obvious with high concentration of SO₂ under NH₃-rich condition.Meanwhile,the enhancing effect of acidic H₂SO₄ seeds on SA formation also became less important with the presence of SO₂/NH₃.Neutral Al₂?SO₄?₃ seeds had no obvious effect on SA formation.The enhancing effect of the oxidation products of SO₂ and the inhibiting effect of Al2O3 were antagonistic.Under NH₃-poor condition,the inhibition ratio of Al2O3 on SA formation decreased from 39%to 24%with SO₂,while under NH₃-rich condition this phenomenon was only observed in experiment with an excess of SO₂.?2?Effects of SO₂/NH₃/NO_x on the formation and hygroscopicity of SOA were further studied in different volatile organic compounds?VOCs?systems.SO₂ contributed to the formation of both inorganic salts and SOA in a-pinene or toluene photo-oxidation experiments.However,the role of NH₃ on aerosol formation depended on the type of VOCs.NH₃ had little effect on aerosol yield but slowed the aerosol formation process in a-pinene system,while it increased the amount of aerosols by about 200%in toluene system.The presence of SO₂ increased the hygroscopicity of SOA in both a-pinene system and toluene system,while NH₃ had little effect on the hygroscopicity.In a-pinene photo-oxidation,the high concentration NO_x reacted with organo-peroxy radicals and generated volatile organic products,and therefore,suppressed SOA formation.However,the high concentration NO_x increased SOA and sulfate formation in heterogeneous reactions due to the synergetic effect of mineral dust and NO_x.In toluene photo-oxidation,under NH₃-rich and winter-like?Low-temperature and High-RH?conditions,h:igh concentration NO_x enhanced secondary aerosol formation,especially ammonium nitrate.Thus,the effect of SO₂ on contribution to the formation of haze was stronger.?3?The removal capacity of the functionalized molecular sieves for aerosols was investigated.Experimental results showed that the removal capacity of modified MCM-41 was obviously larger than that of the unmodified MCM-41.The removal capacity for H₂SO₄ was larger than that for Al₂?SO₄?₃,which maybe result from the different surface properties of the two seeds.There was stronger removal capacity to acidic seeds by amino modified MCM-41.It could effectively inhibit the acid-catalyzing effect in atmospheric environment,further could inhibit the formation of SOA,thus reduced the generation of haze.