Observational Study On Optical Properties Of Aerosol In Nanjing

The observation study on aerosol optical properties in Nanjing was carried out.First,the temporal and spatial variations of aerosol optical properties in Nanjing were discussed.The affecting factors of optical properties and the sources of PM2.5 extinction in Nanjing were analyzed.The absorption enhancement of black carbon(BC)and the contribution of brown carbon(BrC)to the absorption were assessed.And finally aerosol optical properties during the haze were studied.Aerosol optical properties showed significant seasonal and complex diurnal variation in northern suburb of Nanjing.The scattering and absorption coefficients(Bsca and Babs)were higher in fall and winter and lower in spring and summer.Haze happened frequently in winter with minimum average atmospheric visibility.The diurnal variation of Bsca and Babs showed obvious multimodal distribution.The single scatter albedo(?532)changed little in the four seasons with minimum values in the early morning and afternoon.In summer and fall,aerosol was dominated by fine particles.The particle size increased in winter with the largest value during the rush hour of afternoon.Fresh air masses were abundant in summer with minimum Angstrom absorption(Aabs).But,Aabs had no obvious diurnal variation.The characteristics of seasonal and diurnal variation might be affected by meteorological factors,boundary layer change and pollution source emission.In contrast to the Hebei Xianghe site,Babs?Bsca??532?Asca and Aabs with different diurnal variation were higher than that of northern suburb of Nanjing,which reflected the difference of aerosol optical properties between the Yangtze River Delta and Beijing Tianjin Hebei region.Comparing aerosol optical properties of 2013 and 2014 summer in Jiangxinzhou site,the Babs and Bsca in 2013 were lower than the values in 2014.In the summer of 2013,the contribution of absorption to the aerosol extinction increased,and aerosol was dominated by fine particles with higher atmospheric visibility and clean air.In the summer of 2014,aerosol loading increased with serious aged particles.During the Asian Youth Council,Babs and Bsca decreased,but increased during the Youth Olympic Game,which indicated the notable effect of atmospheric environment on aerosol optical properties.The aerosol optical properties in Nanjing were affected by various factors such as meteorological factors,chemical component,particle size distribution,refractive index and so on.In the northern suburb of Nanjing,aerosol from easterly winds had larger ?532 and Asca.The wind direction had little effect on aerosol optical parameters of Jiangxinzhou site of 2013.When the relative humidity was less than 70%,the atmospheric visibility was inversely proportional to aerosol dry scattering and extinction coefficient.The aerosol extinction hygroscopic growth factor(fext(RH))had obvious seasonal and regional differences.The results of summer in northern suburb of Nanjing showed:when the air mass come from the rural areas such as Henan and Anhui province,Babs?Bsca??532 and Asca increased and the contribution of sulfate to extinction increased by 58%with reduced visibility in the northern suburb of Nanjing.Air mass cluster analysis found that more than 70%of air masses in summer in the northern suburb of Nanjing come from ocean with clean air.In winter,almost all air masses were from the mainland with high aerosol loading.In 2014,Jiangxinzhou site was dominated by shorter propagation distance air masses which were slow to spread.The regional pollution had a greater impact.The correlation analysis showed that Babs and Bsca were significantly related to the secondary inorganic ions in the northern suburb of Nanjing.In fall and winter,the combustion source contributed greatly to atmospheric extinction.In spring and summer,the dust affected atmospheric extinction.Secondary aerosol,biomass combustion and motor vehicle emissions were the main contributors to the extinction of PM2.5 in Jiangxinzhou site.Chemical apportionment showed sulfate and organic matter were the main contributors to PM2.5 in the northern suburb of Nanjing,and the contribution of nitrate enhanced at Jiangxinzhou site.It was found that Babs and Bsca were linearly related to aerosol number concentration,surface area concentration and mass concentration with certain temporal and spatical variation by using full size distribution of PM2.5 in Nanjing.The effective refraction index of aerosol in the northern suburb of Nanjing was retrieved,and its diurnal variation and the correlation with the geometric mean diameter and ?532 were analyzed.Based on two methods,the absorption enhancement of black carbon in Nanjing area and the contribution of brown carbon to light absorption were studied.Based on the combination of TD-SPAMS-PASS,it was found that the mass fraction remaining(MFR)of volatile components in PM2.5 varied greatly with heating temperature,and most organic compounds and inorganic salts all evaporate at 250?.The contribution of volatile components to light absorption is about 34%.In the summer of 2014 at Jiangxinzhou site,the absorption enhancement factor of BC(Eabs-781-TD)was 1.53 + 0.03,which might be affected by pollutant sources.The contribution of BC,coatings and BrC to the absorption(405nm)was 62.7%,32%and 5.3%,respectively.The mass scattering efficiency of PM2.5 in winter is the highest and lowest in spring in the northern suburd of Nanjing.Based on the mass absorption cross section,the MAC of total aerosol and BrC in Nanjing area showed obvious seasonal variation,with the largest in winter and the smallest in summer.The absorption enhancement factor of BC(Eabs-781-MAC)was 1.66±0.16?1.51±0.10?1.28±0.10 and 2.29±0.16 with seasonal variation in spring,summer,autumn and winter.Eabs-781-MAC of summer in the northern suburb of Nanjing was close to the value in Jiangxinzhou site.The contribution of BC,coatings and BrC to the aerosol absorption in 405nm has obvious seasonal characteristics.In winter,the contribution of coatings was greater,while the contribution of coatings in spring and autumn decreased.The contribution of BrC was rising because of combustion and biomass burning.The contribution of BC,coatings and BrC to light absorption in summer is close to in NanjingDuring the haze period,the northern suburb of Nanjing was controlled by the air mass originating from the inland with short distance and slow speed which resulted in aerosol accumulation and Babs and Bsca increasing.During no haze period,the air masses come from marine areas which brought clean air in spring and summer;however,in fall and winter,air masses were originated from Xinjiang,the north of Inner Mongolia with cold air to south,the decrease of RH and increase of visibility.In addition to in summer,the haze process was ended by rain.In the summer,fall and winter haze days,the size of aerosol shift to larger size,but haze days 1 in spring,the smaller particle increased and resulted in Asca enlarge.In autumn and winter,the contribution of mobile source in haze days was greater,while in spring and summer,the contribution of stationary source increased.Photochemical transformation of gaseous precursors affected by relative humidity and high concentration pollutants.