Study On Climate Effects Of Black Carbon Aerosol And Their Sensitivity To Size Distribution And Optical Parameters Over China

Black carbon aerosol(BC)comes from the incomplete combustion of fossil fuel and biomass containing carbon and it plays an important role in the climate system.BC can effectively absorb solar radiation at visible and infrared wavelengths and thus heat atmosphere,influencing both climate and air quality.BC can also influence the atmospheric circulation by changing cloud albedo when acting as cloud condensation nucleus.BC in China has caught pervasive attention internationally due to the large emission there.RIEMS2.0 is used here to study the climate effects of BC and their sensitivity to emission,size distribution and optical parameters over China.In this article,the RIEMS 2.0 model,source emission in 2006 and 2010 are used to simulate the distributions and climate effects of BC and total anthropogenic aerosols over China.The comparison between the results forced by source emissions in 2006 and 2010 also reveals the sensitivity of the climate effects to source emission.The results are shown as follows:(1)compared with those in 2006,the annual average surface concentrations of BC increase over central and eastern China with maximums of 10.90?g/m3;the annual aerosol optical depths(AOD)of BC increase over some areas of East China with extremes of 0.006.(2)For the regional average results in 2010,the Rs of BC and the total aerosols at the top of the atmosphere over central and eastern China are 0.29 and-1.1 W/m2,respectively.Compared with those in 2006,the radiative forcings(RFs)of BC in 2010 are both enhanced,while that of the total net RFs are weakened over East China mostly.(3)The warming effect of BC is enhanced over most of the areas in China and the maximum value comes to 0.3K.The net radiative effect of the four anthropogenic aerosols generated the annual average reduction and the maximum reduction are-0.096 and-0.285 K,respectively,for the surface temperature in 2006,while in 2010 they are-0.063 and-0.256 K,respectively.In summary,the change in source emission lower the cooling effect of anthropogenic aerosols,mainly because of the enhanced warming effect of BC and weakened cooling effect of scattering aerosols.A size-resolved scheme(0.15,0.41,0.96 and 5.4?m)of BC has been developed in a regional climate model,RIEMS2.0,based on observational data.This scheme has been proved to be better than the previous uniform size scheme in simulating BC concentrations in China.The differences between the uniform and the size-resolved schemes can be summarized by the study-domain means(ranges).The simulated direct surface radiative forcings(SRFs)using size-resolved scheme are weakened in ranges of 0.08-0.56 W/m2.The warming effect of BC becomes weaker by-0.04--0.16 K over some areas of North China and Southwest China.The difference in the BC-induced precipitation between the two schemes varies irregularly from region to region,ranging from-2.4 to 3.2 mm/d.The earlier uniform scheme usually overestimates BC concentrations,direct RFs,and warming in many regions due to its crude assumption on BC size.With the size-resolved scheme,the BC radiative properties and the climate effect are reassessed and the results are summarized as follows:BC aerosols mainly concentrate on the heavily industrialized North China,the YRD,and the Sichuan Basin.The surface concentrations of BC vary from 1 to 8?g/m3 over North China and East China.Some high BC values appear in the lower reaches of the Yellow River and Yangtze River,as well as the Sichuan Basin,where the maximum BC concentration is 13.07?g/m3.The direct climate effects are shown as follows:The regional mean all-sky and clear-sky column radiative forcings(CRFs)are 1.27 and 1.39 W/m2,respectively;The regional average values of all-sky and clear-sky SRFs are-0.84 and-1.00 W/m2,respectively;Over most areas in China,BC increases the temperature in the range of 0.04-0.24K;The precipitation decreases over South China with the value from-0.5 to-2.5 mm/d,while over the areas of the middle and lower reaches of Yangtze River,the precipitation increases with a maximum of 3.35 mm/d.When it comes to the direct and indirect climate effects of BC:The positive RFs can reach 6 W/m2;Over most areas of East China and North China,the warming effect of BC is evident,with a temperature increase of 0.04?0.20K.The precipitation increase by BC is obvious in South China and Northeast China with 0.08 and 0.13mm/d,respectively.The optical parameters of BC depend on its sizes and refractive index.By using Mie theory,the optical parameters of BC in each size of the size-resolved scheme are calculated.The new parameters are used in the model to simulate the concentration distribution,RFs and climate effects of BC.The comparison between the results forced by two optical parameters schemes also reveals the sensitivity of the climate effects to optical parameters.Compared with the previous optical parameter scheme,the simulations of the new scheme have changed.The concentrations of BC in the first mode increase obviously while those of the other three modes decrease.In the respective of statistics,the changes of column burdens of BC in four modes are 0.085,-0.095,-0.089,-0.054 mg/m2.The AOD of BC vary from-0.0004 to-0.0064 and the regional average variation is-0.0019.The clear-sky TRF of BC are weakened in the value of 0.03 W/m2 averaged over the domain while the all-sky TRF of BC are enhanced of 0.06 W/m2 in average.The warming effect of BC becomes weaker when using the new scheme by-0.04K to-0.24K.When using the new optical parameters scheme,the regional average surface concentrations of BC in four modes are 0.372,0.264,0.055 and 0.004?g/m3.The first mode and the second mode account for 53%and 38%,respectively.The surface concentration and column burden of total BC are 0.69p?g/m3 and 0.28 mg/m2.The regional average direct RFs of BC at the top of the atmosphere are 0.49 W/m2 under clear-sky and 0.36 W/m2 under all-sky averaged over the domain.Over most areas of Central China,North China and East China,BC may increase the temperature in a range of 0.05?0.15K;while over South China,BC shows cooling effect.In average,the precipitation variations cause by BC over East China,North China,South China,Northeast China and West arid/semi arid areas are-0.83,-0.05,-0.11,-0.13 and 0.01 mm/d.In winter,the warming effect of BC is evident especially over the areas between Yangtze and Huanghe River with the maximum of 0.42K.In summer,the precipitation increase caused by BC is obvious over some Southern areas of China;while over some areas near Yangtze River,the precipitation decreases.As a whole,the variations of circulation,pressure and temperature show a good correspondence.