Aerosol Optical Properties And Mixing State In The Northern Suburb Of Nanjing

Based on the data of scattering coefficient,black carbon mass concentration and atmospheric single particle measured at the northern suburb of Nanjing from 2015 to 2016,this paper discussed the aerosol scattering coefficient and its related parameters in this area.It quantitatively analyzes the variation characteristics of aerosol absorption characteristics in four seasons in this area.The source of pollution and the change characteristics of main parameters during the pollution process are discussed.Finally,the mixing state and sources of winter aerosols in this area are analyzed.The following conclusions are obtained:?1?During the observation period,the daily average aerosol scattering coefficient reached a maximum of 877.6 Mm^-1,which was about 18 times the lowest daily average(47 Mm^-1).In January 2015,the average value of scattering coefficient was?359.52±254.24?Mm^-1,and the high value was mainly due to the aggregation of sol particles in polluted weather,while in autumn and winter 2016,the average aerosol scattering coefficient was low,mainly due to the removal of precipitation.?2?During the observation period,the range of??450-700 nm?was 0.3?2.0,with an average value of?1.24±0.22?.The average of b?550 nm?during the observation period is?0.12±0.01?.The aerosol is mainly composed of fine particles with particle size less than 1.5?m.During the observation period,the influence of biomass combustion on aerosol particles is relatively small in spring,while the influence of biomass combustion on aerosols can not be ignored in summer.The influence of biomass combustion on aerosol particles is obvious in autumn,and there are some biomass combustion events.The frequency distribution of AAE in winter is only within the range of<1.6,which shows that there are almost no biomass combustion events in winter.?3?During the pollution process from January 22,2015 to January 30,2015,the changes in the aerosol scattering coefficient and absorption coefficient were consistent with the changes in the mass concentration of PM_2.5.The aerosol scattering plays a dominant role in atmospheric extinction.The average value of AAE?470-880 nm?during the pollution period is 1.32,indicating that the main pollution source is the combustion of fossil fuel.The main reason for the high PM_2.5mass concentration on January 22 and 30 is the emission of biomass combustion.From 5:00 to 14:00 on January 25,the moisture absorption growth of fine particles makes the PM_2.5mass concentration continuously decrease.?4?In December 2015,the main winter pollution source in the northern suburb of Nanjing was coal combustion,followed by vehicle exhaust emissions,with the contribution rate of47.5%respectively.Industrial process sources and secondary non-polar pollution sources account for 16%and 12.7%respectively.The contribution rate of other sources,biomass combustion sources and dust sources is less than 10%.In the process of heavy pollution in winter in December 2015,the proportion of coal combustion sources increased with the increase of PM_2.5concentration in each stage.From December 26 to 27 the PM_2.5decreased continuously,the contribution rate of coal-fired source decreased from 29.4%to 14.4%,and the contribution rate of motor vehicle exhaust emission source and other sources showed an upward trend.