Investigation On Aerosol Hygroscopicity During Winter And Summer Seasons In Guangzhou

Hygroscopic properties of aerosol particles are important for determining aerosol size distribution,and thus influence the scattering and absorption coefficients,the formation mechanism of cloud condensation nuclei,the atmospheric heterogeneous chemical process and human health.In this study,hygroscopic properties of aerosol particles at an urban site in Guangzhou,China,were measured using a Hygroscopic Tandem Differential Mobility Analyzer(H-TDMA)system during winter and summer.At relative humidity of 90%,particles of 40-200nm were observed,the distribution of particle hygroscopic growth factor(GF)was in three mode,which was mainly divided into non hygroscopic mode(GF<1.1,NH Mode),GFNH was about 1 during the observation.Less hygroscopic mode(1.11<GF<1.33,LH Mode),the average GF of LH group was about 1.23.And more hygroscopic mode(GF>1.34,MH Mode).For more hygroscopic mode particles,with particle size increased from 40 nm to 200 nm,GFMH increased from 1.44 to 1.57.Obvious diurnal variation characteristic was found in this work.GFLH increased significantly during the daytime,GFMH remain at a low value in the same time.Such phenomenon was closely related to the diurnal evolution of the mixing layer and the atmospheric photochemical reactions.Air mass origin cluster analysis shows that aerosol hygroscopicity was also influenced by air mass sources.The diurnal variation of NFNH shows that particles were at a low degree of external mixing or quasi internal mixing during the daytime,and external mixing at night.The particle mixing state was mainly affected by the development of mixing layer.Through the analysis of the effect of different weather conditions on aerosol hygroscopicity.Results show that during clean period and haze period,GF and NFMH characteristics,particle GF-PDF distribution,air mass sources and chemical composition have great differences.GF of clean period was higher than that of haze period.Mainly because that aerosol after long time transmission have more aging time,the generation,transformation and adsorption of hygroscopic material was more.On the basis of the whole aerosol hygroscopic characteristics,this work using aerosol hygroscopic growth factors and ISORRPIA ? models to calculate the liquid water content in the particles,and the results were analyzed with correlation analysis and diurnal variation.The correlation was good between the two methods,R2=0.86,which means the liquid water calculated through H-TDMA was reliable.