Research On Aerosol Optical Properties In Beijing By Using Satellite And AERONET Observation Data

With the rapid development of economy and urbanization,the problem of air pollution in Beijing as well as its surrounding region Bohai,has serious impact on the living environment of human beings.Therefore,the long-term effective observation and study of aerosol optical properties under pollution environment in Beijing are essential to improve the air quality,assess the aerosol radiative forcing from regional to global and understand climate change.In this paper,combined with MODIS data,CALIPSO data and AERONET observation network data,using IDL(Interactive Data Language)data processing methods to study the optical properties of aerosols in Beijing.Firstly,SCA method according to532 nm wavelength attenuated backscatter coefficient?'532(Z)and dual-wavelength signal ratio ? ' was adopted to distinguish aerosol and cloud,and the CLIM method was used to further identify the dust aerosol of a typical dust weather in Beijing on March 8~11,2013,and got the dust recognition results.Then the HYSPLIT model and NAAPS Aerosol model were employed to simulate the dust sources and transmission process,and with the Two-wavelength inversion algorithm retrieved the aerosol optical thickness.Secondly,the direct solar radiation data of AERONET was used to invert dust aerosol optical properties,statistical analyzed the dust aerosol optical characteristics in Beijing from 2001 to 2013 under dusty weather conditions.Finally,with the aerosol optical thickness inverted by the direct solar radiation data of AERONET,and the aerosol single scattering albedo,the complex refractive index,the volume size distribution and other optical parameters inverted by sky diffuse radiation data,statistical analyzed the seasonal variation of aerosol optical properties in Beijing from 2002 to 2013.The results are as follows:(1)The spatial distribution and distribution height of aerosols and clouds can be drawn from the space distribution of the various optical parameters.Combination of SCA and CLIM method can distinguish aerosols and clouds better as well as identify dust aerosols.(2)Analyzed the dust weather on March 9 to 11,2013 illustrated as a typical example,the result showed that: Under the dust weather conditions in Beijing,the depolarization ratio of dust aerosol was between 0.1-0.4,the color ratio was usually greater than 0.3,and the distribution height of dust aerosol was generally below 4km.By using HYSPLIT and NAAPS aerosol model simulation found the dust originating from the south Xinjiang basin and the central and western regions of Inner Mongolia,in line with the westward path typeof the dust weather transmission path in our country.During the dust transmission process,the air quality was impacted by the dust weather significantly in Beijing,and the main pollutants translated from PM2.5 to PM10.The Two-wavelength inversion algorithm was used to retrieve the aerosol optical thickness in Beijing under dust weather situation on March 10 and 11,which were 0.334 and 0.621,respectively.(3)Analyzed the dust weather in Beijing from 2001 to 2013:Account of the dust particles impaction during the sandstorm in Beijing,the aerosol optical thickness value(AOD)is large,which decreases with the wavelength increasing,and the average value is about 1.2 at the wavelength of 440 nm.The 97.62% of aerosol Angstrom exponent gathered below 0.7,indicating that the particles are large during the sandstorm weather in Beijing;the single scattering albedo during the sandstorm increases with the wavelength increasing,and the average value is about 0.93;the real part of the complex refractive index at the wavelength of 675 nm is the most,and the average is about 1.55;and the largest imaginary part is at the wavelength of 440 nm,reaching 0.006;the total asymmetry factor average is about 0.72.The aerosol volume size distribution is a bimodal distribution type during the dust weather in Beijing,mainly concentrates in coarse particles,and the main peak value increases with the aerosol optical thickness increasing,the average radius of the peak is about 2.6?m;Dust weather mainly concentrated in spring and winter in Beijing,and the days of dust weather in Beijing showed a decreasing trend after taking a series of effective dust control means.(4)The seasonal variation of aerosol optical properties in Beijing: The aerosol optical thickness value in spring and winter were greater than that of summer and autumn;The Angstrom exponent in spring and winter were smaller in Beijing,the angstrom index average was minimum in spring(0.93),which mainly because spring and winter are dust-prone season which has plenty of dust particles in Beijing;and the anthropogenic polluting aerosol is the dominant aerosol in summer and autumn which consists of a large number of fine particles,so the Angstrom exponent is large,1.21 and 1.12 respectively.By analyzing the precipitation inverted from AERONET data found that smaller precipitation corresponding larger aerosol optical thickness in spring and winter,more precipitation in summer and autumn whose aerosol optical thickness was relatively smaller in Beijing,indicating that rainfall has cleaning effect on atmospheric aerosols.The aerosol volume size distribution showed significant seasonal change in Beijing,fine mode particles were dominant in summer,which were larger than that of other seasons;the coarse mode was evidently dominant in Spring due to the presence of dust particles with relative big sizeparticles,and the maximum volume concentration(0.13?m3?m-2)was in spring,which was about 2.5 times of fine-modal volume concentration.(5)The asymmetry factor of the climate and radiation models is 0.66 in Beijing at the wavelength of 440,675,870,1020nm;The seasonal mean single scattering albedos are0.90,0.92,0.88,0.86 respective at the four bands;the real part of the complex refractive index is1.52,and the imaginary part is 0.0118.