Numerical Simulation On Secondary Organic Aerosol In Typical Coastal City

Nowadays,combined air pollution characterized with highconcentrations of ozone (O3) and fine particles (PM2.5) have made adverseimpacts on environment and human health. As a megacity, Shanghai hasencountered frequent haze phenomenon in recent years, and PM2.5makes asignificant contribution to which. Organic carbon is an importantcomposition in PM2.5, in which secondary organic aerosol (SOA) is themost uncertain part due to its various precusors and complicated formationmechanisms that are not well understood yet. SOA can cause haze problemand affact human health due to its strong polarity, hygroscopicity andsolubility. The formation of SOA include the oxidation of volatile organiccompounds (VOCs) that produce condensable products and theirabsorbtion/partioning between gas and particles. Triditional oxidantsinclude hydroxylradicals(OH), nitrate radicals(NO3), and ozone (O3). Butlatest researches proved that chlorine (Cl) atoms has potential of VOCsoxidation, which is compatible to OH or even faster than OH in specificconditions. Therefore, it is meaningful and crucial to study Cl relatedchemical reactions and its impact on SOA formation in typical coastalcitiesthat has abundant sea-salt aerosols.The atmospehric chemical mechanism considering chlorine chemistry,CACM_CL, was developed based on CACM. The box models were builtbased on CB05CL and CACM_CL to simulate chlorine chmesitry intypical costal city of Shanghaiwith four scenarios imagined according tothe characteristics of season and site. The effects of meterological factors,other pollutants, and combined factors on chlorine matters were also testedrespectively. The simulation results by two mechanisms were compared. The results show that Cl2was not affected by meterological factors andother pollutants. Cl increased first, and then decreased, with relative highconcentrations at rural areas, which lead to the lower ClO, HOCl and HClat urban areas that that at rural areas. Cl was similarly simulated at urbanareas by two mechanisms, but CACM_CL predicted higher Cl at ruralareas due to its reactive OH radicals. Temperature could affect Cl, ClO,HOCl and HCl, especially for ClO and HOCl, while the effects of pressurewas negeligble. Relative humidty showed negligible effects on Cl, whileClO and HClO incresed with increased relative humidity. Other pollutantssuch as O3and NO could affect chlorines as well, especially for Cl inCACM_CL mechanism. ClO, HOCl incresed with increased O3and NOexcept for NO higher than0.01ppm in CACM_CL mechanism. Thecomplex effects of high temperature, high relative humidity and highconcentrations of O3and NO were obvious,which would increase ClO andHOCl concentrations and affect Cl concentrations simulated byCACM_CL. Based on the estimation, the SOA formation yields fromchlorine atoms at rural areas were higher than that at urban areas, andwhich at areas with low concentrations of biogenic VOCs were higher thanthat at areas with high concentrations of biogenic VOCs. According to thepreliminary boxmodel simulation, SOA formed through the oxidation ofisoprene by Cl could reach0.06-0.1%of organic carbon from the basesimulation, which might be affected by high temperature and high relativehumidity in the summer, the increased O3and NO, and the combinedfactors as well. And these estimations need further investigations andverifications through three dimensional simulations.