| The Aerosol Single-scattering Albedo(SSA)is the ratio of the aerosol scattering coefficient to the total extinction coefficient,referring to the characterization of aerosol absorption,which determines the positive and negative aerosol radiative forcing and accurate assessment of aerosol radiative forcing in climate change is of great significance.In this paper,the Aerosol Robotic NETwork(AERONET),the Chinese Sun Hazemeter Network(CSHNET)and satellite OMI data were used to conduct systematic and comprehensive analyses of the changing characteristics of SSA,including annual,seasonal,and long-term trends analysis.And the SSA retrieved by the OMI compared with ground-based datas(AERONET and CSHNET).Due to SSA is based on inversion algorithms depodding on assumption,the level of agreement consistency can only regard as a measure of consistency in the measurement of the same physical parameter by fundamentally different remote sensing approaches Seasonal changes of Beijing and Xianghe were similar to the annual variations,but Xinglong and Lanzhou SSA all showed an increasing pattern from 440 nm to676nm and a decreasing parttern from a 676 nm to 1020 nm during the winter.Because of heating in winter,the type of absorbing aerosols had changed in Xinglong and Lanzhou.In addition,the annual and seasonal variaties of SSA exhelled that the SSA in Beijing and Xianghe had an increase year by year,while the changes in Xinglong and Lanzhou are relatively small,and SSA was lower in autumn and winter and was higher in spring and summer.This paper adopted AERONET SSA of 440 nm,676nm,870 nm and 1020 nm to analyze the relationship between SSA and wavelength in typical regions of northern China(Beijing,Xianghe,Xinglong and Lanzhou)from 2004 to 2016.The results have shown that the SSA value,in Beijing and Xianghe areas,first increases with the wavelength and then decreases,reaching a maximum at 676 nm.The SSA spectrum exhibited that aerosol composition in Beijing and its surrounding areas is more complex and contains large amounts of black carbon(BC)and brown carbon(BrC);Xinglong SSA did not change significantly with wavelength,indicating that the aerosol in Xinglong area contained less absorbing aerosol;Lanzhou SSA increased slowly with the wavelength,indicating that Lanzhou aerosol contained large particle size absorption aerosols(such as fine dust,sand,dust).However,seasonal variations of the four stations SSA with the change of wavelengths were different.Based on AERONET and OMI data from October 2004 to December 2016,the trend of aerosol SSA and comparison agreement with AERONET and OMI at the north of china(Beijing,Xianghe,Xinglong and Lanzhou)were analyzed.The SSA annual mean of four sites were: Beijing 0.89±0.04(AERONET)and 0.90±0.04(OMI);Xianghe 0.89±0.04(AERONET)and 0.91±0.04(OMI);Xinglong 0.92±0.04(AERONET)and 0.91±0.04(OMI);Lanzhou 0.91±0.04(AERONET)and 0.90±0.04(OMI).All four sites showed the same seasonal variations,with high values in summer and low values in winter.Due to the limited data,the monthly average can not simply use to analyze the annual trend,we need to screen the data and remove the seasonal variation.The result showed that ground-based network and satellite had different time scales at both Beijing and Xianghe,while the OMI at Xinglong and AERONET at Lanzhou were meet the data requirements for trend analysis.The SSA of all four sites had the significant increases,indicating that the absorption of aerosol in the norther China have weaken and scattering have been enhanced in recent years.In particular,the AERONET and OMI retrievals of SSA were found an upward trend in four seasons at Beijing,but the absorption in autumn and winter was enhanced at Xianghe.In addition,due to the slight difference between AERONET and OMI,the data of AERONET and OMI were compared to accuracy of the results.The data of Xianghe revealed much bigger gap between the two inversions,which 30% of data agree within the absolute difference of ±0.03,and 55% agree within the difference of ±0.05;and Beijing 46% agreement within ±0.03 and 68% agreement of ±0.05,Xinglong 50% agreement within ±0.03 and 78% agreement within ±0.05;the data of Lanzhou was much better consistent,which 51%(86%)of data made agreement within the difference of ±0.03(±0.05).In total,the data at sites which were more affected by human activities were consistently poor.The paper also used the 500 nm SSA of OMI and CSHNET at the 11 sites(Beijing,Xianghe,Shenyang,Fengqiu,Lanzhou,Shapotou,Jiaozhou Bay,Shanhai,Xishuangbanna,Taoyuan andYanting)from 2004 to 2011.An analysis of the colocated retrievals at the northwest and the sourthwest revealed that about 33%-50% and 48%-70% of OMI-CSHENT matchups agree within the absolute difference of ±0.03 and ±0.05,which was poor;at the northeast and the sourtheast showed that about 58%-65% and 84%-94% of matchups agree within ±0.03 and ±0.05,which was best match;and the remaining sites were 43%-58%(±0.03)and 78%-86%(±0.05).A total of 585 matchups were available at 11 sites,which 53% and 78% matchups agreed within ±0.03 and ±0.05.There are also research results showing that when UV-AI index retrieved by OMI was between 0.8 and 1.2,the absolute difference of ±0.03(±0.05)was smallest;and when the CSHNET measureed the AOD value higher,the OMI-CSHNET matchups agreed better and the absolute difference reduced from 0.05 to 0.03.In addition,this study shows that OMI has high accuracy in China.Therefore,the temporal and spatial distribution charateristics of SSA data from 2005 to 2017 at 500 nm and 388 nm retailed by OMI were studied.The result showed that: Northeast China,East China and South China were SSA high value areas,and SSA decreased year by year.The value of SSA was followed by Central China,and the trend of SSA varaged by year was also down.And North China,Northwest and Southwest China were located in the low value aera of SSA,but Sichuan and Chongqing in the southwest region had higher SSA value than the surrounding area because of ited geographical conditions. |
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