利用FY-4A卫星光学数据对中国近地面PM2.5浓度的估算和检验分析

对FY-4A卫星的气溶胶光学厚度（AOD）产品进行检验，并根据卫星相关观测资料，通过改进后的PMRS方法，反演得到中国近地面PM_2.5质量浓度网格化分布。结果表明，FY-4A卫星反演不同站点AOD与地基观测网（AERONET）观测结果吻合较好，但存在一定的低估或高估现象，相关系数区间为0.54—0.87。将细粒子比（FMF）以0.4为界进行划分，FMF＞0.4时，拟合结果较FMF≤0.4时更接近于AERONET观测结果；但FMF≤0.4时，卫星反演的AOD稳定性优于FMF＞0.4时。通过引入AOD的大小，改进FMF＞0.4时对细粒子柱状体积消光比（VE_f）的估算算法，并通过改进后的PMRS方法对中国近地面PM_2.5浓度进行逐时反演，其反演结果和地面观测结果相关较好，其中，乌鲁木齐、石家庄和徐州观测点的相关系数均高于0.7，但数值上仍存在高估或低估，误差结果由多种因素决定。空间分布中，卫星反演的中国2019年近地面PM_2.5浓度月均值与近地面观测的结果有较好的对应关系，二者逐月演变趋势基本一致，基本可以反映出中国近地面大气细粒子的空间分布，特别是秋、冬季京津冀周边区域、汾渭平原等污染高值区均与地面观测对应较好。 

Estimates and verification of surface PM2.5 mass concentration in China based on FY-4A satellite optical products

In this study, the aerosol optical depth (AOD) products of the FY-4A satellite are evaluated base on the satellite data, gridded distribution of near surface PM_2.5 mass concentration in China is retrieved using the improved PMRS method. The results show that the FY-4A satellite retrieved AOD and AERONET observations agree well at various sites, although there exist certain underestimates or overestimates. The correlation ranges from 0.54 to 0.87. FMF is divided by the criterion of 0.4. When FMF＞0.4, the fitting results are closer to the observations of AERONET than that when FMF≤0.4; however, when FMF≤0.4, the AOD stability of satellite retrievals is better than that when FMF＞0.4. By introducing the size of AOD, the estimation algorithm for VE_f is improved when FMF＞0.4. Using the improved PMRS method, hourly retrievals of China near-surface PM_2.5 are better correlated with the surface observation. Among all the results, the correlations between retrievals and observations are higher than 0.7 at Urumqi, Shijiazhuang and Xuzhou. However, there are overestimates or underestimates in the retrievals and the errors are determined by various factors. Regarding the spatial distribution, the national average of near-surface PM_2.5 of satellite retrievals has a good correspondence with the results of near-surface observations in 2019. The monthly variation trends of the two are basically the same, which can basically reflect the spatial distribution of the near-surface PM_2.5 in China. Specifically, in autumn and winter, satellite retrievals over the areas around Beijing-Tianjin-Hebei, the Fen-Wei Plain and other high-pollution areas all correspond well with ground observations.