选取2011年中国东部地区428个测站的PM10质量浓度资料,用Terra和Aqua MODIS AOD产品的时间分布作为指示数据,检验日、月、季、年时间尺度下,卫星过境时刻地面PM数据(SATPM)对地面所有时刻数据平均值(ALLPM)的代表性。结果发现,在东部大部分地区,SATPM与ALLPM的相对误差在±20%以内,且Aqua-MODIS代表性更好。此外,结合两颗卫星的数据,经拟合订正获得了新的日、年时间尺度上PM10质量浓度数据,将其与ALLPM的相关系数从0.87和0.83提高到0.90。此检验结果对于检验卫星数据反演的PM2.5的代表性也有一定指导意义。
Two channels of the Cloud Aerosol Polarimetric Imager,onboard the TanSat-Chinese carbon dioxide observation satellite,are designed to detect the polarization state of radiation reflected by the earth-atmosphere system in a single-viewing angle.Aiming to understand how the earth and atmospheric parameters affect the polarization state of radiation,we conduct a sensitivity analysis of the polarized reflectance at the top of atmosphere(TOA)with respect to the aerosol microphysical parameters,atmospheric profiles,and surface polarization properties.It is found that(1)the TOA polarization reflectance at 0.66 lm is most sensitive to the real part of the aerosol complex refractive index,the mean radius of the fine mode aerosol particles,as well as atmospheric pressure and temperature profiles;(2)the TOA polarization reflectance at 1.64 lm is sensitive to the volume ratio between the coarse mode and fine mode particles as well,but it is not sensitive to atmospheric profiles;and(3)surface polarization properties have a relatively weak influence on the TOA polarization reflectance at both 0.66 and 1.64 lm.
The hygroscopic properties of mixed aerosol particles are crucial for the application of remote sensing products of aerosol optical parameters in the study of air quality and climate at multiple scales. In this study, the authors investigated aerosol optical properties as a func tion of relative humidity （RH） for two representative me tropolises： Beijing and Hong Kong. In addition to the RH data, mass concentrations of PM10 （particulate matter up to 10 utm in diameter） and aerosol scattering extinction coefficient （aext） data were used. The relationship between the mass scattering extinction efficiency （MEE, defined as O＇ext/PMl0） and RH can be expressed by regression func tions asf= 1.52x ＋ 0.29 （re= 0.77）,f= 1.42x ＋ 1.53 （re= 0.58）,f= 1.19x ＋ 0.65 （re= 0.59）, andf= 1.58x ＋ 1.30 （re = 0.61） for spring, summer, autumn, and winter, respec tively, in Beijing. Here, f represents MEE, x represents I/（1-RH）, and the coefficients of determination are pre sented in parentheses. Conversely, in Hong Kong, the corresponding functions are f= 1.98x- 1.40 （r^2= 0.55）,f = 1.32x - 0.36 （r^2 = 0.26）,f= 1.87x - 0.65 （r^2 = 0.64）, and f= 2.39x - 1.47 （r^2 = 0.72）, respectively. The MEE values for Hong Kong at high RHs （RH 〉 70%） are higher than those for Beijing, except in summer; this suggests that aerosols in Hong Kong are more hygroscopic than those in Beijing for the other three seasons, but the aerosol hy groscopicity is similarly high in summer over both cities. This study describes the effects of moisture on aerosol scattering extinction coefficients and provides a potential method of studying atmospheric visibility and ground level air quality using some of the optical remote sensing products of satellites.
LI Cheng-CaiHE XiuDENG Zhao-ZeAlexis Kai-Hon LAULI Ying
