Physicochemical Characteristics Of Aerosol Components And Their Effects On Atmospheric Extinction In The Yangtze River Delta Of China

Recently,visibility in clear skies has been found to have decreased over land globally from 1980 to 2010.Atmospheric visibility degradation is an important environmental issue due to its demonstrated association with air pollution.The reduction in visibility is not only an aesthetic problem but also an important indicator of deteriorating ambient air quality in urban areas.Its direct inducement comes from a series of haze and other weather phenomena caused by high concentrations of particulates in the atmosphere,which has a great impact on people's lives.In addition to meteorological elements,visibility is mainly affected by the absorption and scattering of light by atmospheric aerosol components and gaseous pollutants.Therefore,it is of great significance to discuss the physicochemical characteristics and optical properties of atmospheric aerosol components through joint regional observations to understand the air quality conditions in the Yangtze River Delta and to assess the climate effects of atmospheric aerosols.Focusing on the Yangtze River Delta(YRD),the size distribution,chemical composition and relative humidity were measured in Nanjing,Suzhou and Lin'an from January 9 to 31,2015.To explore the physical and chemical characteristics of water-soluble ions,OC and EC in the PM2.5 in winter and potential sources of pollution contribution.Combining with the conditions of high humidity and heavy pollution during the observation period,the sources and formation mechanisms of secondary inorganic ions in mist and haze days were studied.Based on the joint observational data of the region,the contribution of particulate matter to atmospheric extinction coefficient in the Yangtze River Delta region was quantitatively evaluated.Also,The merits and weaknesses of three parameterization schemes and the optical properties of the aerosol under different mixing models of black carbon were calculated and discussed in this study.The results show that the fine particulate pollution in the Yangtze River Delta region is heavy,and it has intensified in recent years compared with previous researches.The order of main ion concentrations in Nanjing,Suzhou,and Lin'an Station is basically the same:NO3->SO42->NH4+>Cl->K+.The acidic ions were mainly existed as(NH4)2SO4 and NH4NO3.There were a good correlation between OC and EC(R2>0.7).The average OC/EC rates in Nanjing,Suzhou,and Lin'an stations were 4.0,5.1,and 4.3 respectively.Carbonaceous aerosol sources are motor vehicle exhaust and coal combustion.Potential sources of pollutants during the observation period were mainly concentrated in the Yangtze River Delta and its surrounding areas,including Shandong,Henan,Anhui,Jiangxi,and Zhejiang.The formation of high concentration of sulfate could be explained by heterogeneous reaction due to high correlation between relative humidity and SOR,which could be favored by higher LWC in mist days.The correlation of nitrate to the concentration of N4+ was relatively high,by liner fitting the excess NH4+ and NO3-we may come to the conclusion,which is based on the previous studies that the nitrate was most probably formed via the homogeneous gas-phase reaction between ammonia and nitric acid.The weaker acidity of the fog days may be more conducive to the occurrence of this reaction.The study found that the atmospheric extinction coefficients of Nanjing,Suzhou,and Lin'an stations were 621.81,763.38,and 744.91 M m-1,respectively.POM(organic matter),ammonium sulfate,and ammonium nitrate contributed the most to the extinction coefficient.Among three parameterization schemes,the ?-EC-Mie model objectively reflects the changes in the law of visibility,as the model considers both the chemical composition and size distribution of particles,and its predominant merit is derived from the fact that it is calculated without an empirical formula,which may eliminate the computational errors caused by the uncertainties of coefficients.The mixing method of black carbon has little effect on the extinction and scattering coefficient of aerosol particles,but it has a significant effect on the absorption coefficient.The increase of relative humidity in the environment is an important factor in changing the extinction coefficient of aerosols.The extinction coefficient and scattering coefficient will increase significantly,no matter what kind of mixing model is,their growth rate is roughly the same,but for the absorption coefficient,the growth rate is related to the mixing model.The growth rate of internal mixing is much greater than other hybrid methods.