Research On The Influence Of Aerosols On Solar Radiation In Beijing In The Past Ten Years

The data of PM2.5 concentration and surface radiation(Rs)from Institute of Atmospheric Physics site of Beijing in 2005-2015 were used for studying the interaction of aerosol and radiation in Beijing.Using the SBDART(Santa Barbara DISORT Atmospheric Radiative Transter)radiation transmission model and aerosol optical properties obtained from the AERONET Beijing site,to calculated the attenuation of total radiation(Rs),ultraviolet radiation(UV)and photosynthetically active radiation(PAR)by aerosol.And then,We evaluated the radiation forcing by composite aerosol and black carbon aerosols(BC),and quantified the aerosol radiative forcing in UV and PAR zones.The results are as follow:1.The observation data of aerosol and radiation were used to reveal the long-term changes of aerosol particles(PM2.5),Rs and PAR in the Beijing area during the last ten years.The annual average value of PM2.5 mass concentration in Beijing area was 77.8+59.6?g/m~3in the last ten years.The mass concentration of PM2.5 showed a slight upward trend from 2005 to 2015,but the trend of PM2.5 concentration decreased obviously after 2013.The seasonal variation of PM2.5 concentration was as follows:low concentration in spring and summer,high concentration in autumn and winter.In recent ten years,the annual mean value of Rs in Beijing is 315.6w/m~2,showing an overall upward trend,especially after 2013.The seasonal variation of radiation was as follow:high values appear in spring and summer,low values appear in autumn and winter.When the PM2.5 mass concentration is less than 75?g/m~3,the normalized total surface radiation(Rsn)will decrease by 3.81w/m~2for every increase of PM2.5 mass concentration;when the full range of PM2.5 changes,both Shows a logarithmic relationship.2.The variation characteristics of aerosol optical properties in Beijing area were obtained by observation data from AERONET Beijing station.In recent years,the annual mean values of AOD were 0.61±0.56,0.38±0.35,0.29±0.26,and 0.25±0.22 at 440 nm,675 nm,870 nm,and 1020 nm bands,respectively.In the 440nm band,the seasonal variation law of AOD was follows:summer>spring>autumn>winter.The mean values of?ngstr?m exponent 1.09,the minimum was 0.97 appear in spring and maximum was 1.26 in summer.The average value of SSA in the four bands was above 0.85.Due to the influence of dust and gale weather process,the aerosol was dominated by coarse particles in spring of Beijing,so the concentration of aerosol volume in the peak of coarse mode was higher than that of other seasons,and the?ngstr?m exponent was low in spring.Elevated secondary aerosol concentration and hygroscopic growth of aerosol were found in summer due to the high temperature and humidity,which strengthens the scattering of aerosol and the monthly mean maximum values of SSA appear in August.And the aerosol volume concentration in the peak of fine mode was higher than that of other seasons.A large number of black carbon aerosols were emitted from biomass combustion and coal were found in autumn and winter,which resulting in an enhanced absorption of aerosols and low value of SSA.3.Based on the aerosol optical parameters obtained from AERONET Beijing station,the radiation forcing caused by the composite aerosol and BC during2005~2014 was simulated using SBDART radiative transfer model.Under clear-sky conditions,radiative forcing of composite aerosol at the top of the atmosphere,at the earth surface and in the atmosphere in the Rs,UV,and PAR bands was-24.91±19.80w/m~2,-65.52±.43.78w/m~2,40.61±28.62w/m~2(Rs);-1.09±1.24w/m~2,-6.09±4.37w/m~2,5.01±3.74w/m~2(UV);-14.46±10.96w/m~2,-36.43±24.39w/m~2,2.97±15.32w/m~2(PAR),respectively.The radiative forcing of aerosol was high in spring and summer,and low in winter.For the seasonal variation characteristics,the radiative forcings UV and PAR bands in TOA,BOA and ATM also was high in spring and summer,and was low in winter.The ratio of UV radiative forcing to composite aerosol radiative forcing was shown as:ATM>BOA>TOA;The ratio at top of the atmosphere in the summer was the highest,may be due to the higher SSA in the 440 nm band in summer,which increases the scattering of the ultraviolet band and causes more radiation to be returned to space.Under clear sky conditions,for the seasonal variation characteristics of BC radiative forcings in TOA,BOA and ATM also was high in spring and summer,and was low in winter.The ratio of BC radiative forcing to composite aerosol radiative forcing in the atmosphere remained at68%in June,July and August,indicating that the atmospheric heating effect of aerosols in summer mainly comes from BC aerosols.Especially when the value of SSA(440nm)is less than 0.8,the radiation force on the top of the atmosphere was positive radiation force at some days in the autumn and winter.