Physicochemical Properties And Mixing State Of Ambient Aerosols In Nanjing

Ambient aerosols are an essential constituent in the air and are closely related to global/regional climate,atmospheric visibility and public health.There are obvious differences in transportation,transformation and removal mechanisms of aerosols due to their distinct characteristics(such as size distributions and mixing states).Influenced by various factors,such as meteorological conditions and sources,the characteristics of particles(such as density,shape,hygroscopicity and refractive index)varied constantly.Various aerosols evolved in different ways in the atmosphere,hence,it is essential to discuss single aerosols with high time resolution in real time.Nanjing is an important city in the Yangtze River Delta(YRD),its major emission sources include industrial areas,residential areas,traffic and agricultures.In recent years,the particle matter level in Nanjing still is high,regional and complex pollutions appear frequently.Single-particle data during four seasons and a regional pollution episode were obtained by single particle aerosol mass spectrometer(SPAMS),with the help of meteorological data and PM2.5,the aerosol characteristics during each season,different pollution episodes and specific conditions were analyzed in detail.The major contents and results are showed as follows:(1)Chemical compositions of ambient aerosols in Nanjing exhibited obvious seasonal variations.The five top ranked particle classes during winter,spring and fall were EC-SN,OC.Biomass,NaK-SN and Fe-rich,accounting for 82.8%,92.5%and 88.1%of total particles in each season,respectively.However,EC-SN,NaK-SN,Fe-rich,Biomass and EC-S during summer were abundant,accounting for 88.8%.Seasonal size distributions of some particles were similar.Carbonaceous particles contributed to submicron particles,EC-S concentrated in the size range of 0.2-0.5?m,Fe-rich and MiscMetals particles were more important with increased sizes.ECOC,OC,Biomass and NaK-SN had clearly distinct seasonal size distributions.Ambient particles all mixed with significant secondary species.Enhanced ammonium/chloride/sulfate were found in ECOC and OC/Biomass,MiscMetals and Dust/OC particles in four seasons.Basically,the fractions of particles mixed with nitrate/sulfate changed following as spring>winter>summer>fall/winter>summer>spring>fall.(2)Regional pollution in the YRD were influenced by local sources(emissions within the YRD were included)and long-range transported sources(emissions are located outside the YRD).During different types of pollution,OC had obvious different size distributions,but ECOC exhibited similarly.And long-range transported pollution was more helpful for the growth of OC.Particles mixed with more chloride and nitrate/sulfate in local/long-range transported pollution.(3)Specific conditions could lead to variations in particles.The number fraction of OC in total particles decreased in fog and haze periods while EC-SN and NaK-EC showed the opposite trend,about 2 times larger than clean episodes.Most particles mixed with more nitrate in fog.The reduced rate of the total number fraction of carbonaceous particles changed following as clean>fog>haze,and that in fog was slower with increased sizes.Due to anthropogenic activities,stronger winds and solar radiation,significant variations in the particle counts and size ranges appeared when fog transformed to haze.Carbonaceous particles and Na-K mixed with enhanced secondary species during haze,and obviously were more acidic,especially for the ones with a size range of 0.6-1.2?m.Characteristics of precipitations,like durations and total rainfall amount,influenced particles obviously.When the sources were stable,longer/shorter duration of precipitation with intensities less than 1mm favored the adsorption of secondary inorganic/organic species on particles.Heavy torrential rain had stronger removal of EC than NaK-SN.Particles influenced by continental sources in short-term rainfalls mixed with more nitrate and oxidized organics,while particles influenced by marine sources mixed with more ammonium and sulfate in long-term rainfall.(4)Variations of relative humidity(RH)affected particles.During winter,with the increase of RH,the fractions of EC,ECOC,Ammonium and Fe-rich increased,but the fractions of OC,Biomass,NaK-SN and Dust decreased.Along with the increased RH,most particles mixed with more NH4+ and less C2H3O+,the latter one was consistent with the changes of OC.