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Abstract. The retrieval of aerosol properties from satellite observationsprovides their spatial distribution over a wide area in cloud-freeconditions. As such, they complement ground-based measurements by providinginformation over sparsely instrumented areas, albeit that significantdifferences may exist in both the type of information obtained and thetemporal information from satellite and ground-based observations. In thispaper, information from different types of satellite-based instruments isused to provide a 3-D climatology of aerosol properties over mainland China,i.e., vertical profiles of extinction coefficients from the Cloud-AerosolLidar with Orthogonal Polarization (CALIOP), a lidar flyingaboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation(CALIPSO) satellite and the column-integrated extinction (aerosol optical depth – AOD)available from three radiometers: the European Space Agency (ESA)'s Along-TrackScanning Radiometer version 2 (ATSR-2), Advanced Along-Track Scanning Radiometer (AATSR) (together referred toas ATSR) and NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite, together spanning the period 1995–2015. AODdata are retrieved from ATSR using the ATSR dual view (ADV) v2.31 algorithm, while for MODISCollection 6 (C6) the AOD data set is used that was obtained from merging theAODs obtained from the dark target (DT) and deep blue (DB) algorithms, furtherreferred to as the DTDB merged AOD product. These data sets arevalidated and differences are compared using Aerosol Robotic Network (AERONET) version 2 L2.0 AOD dataas reference. The results show that, over China, ATSR slightly underestimatesthe AOD and MODIS slightly overestimates the AOD. Consequently, ATSR AOD isoverall lower than that from MODIS, and the difference increases withincreasing AOD. The comparison also shows that neither of the ATSR and MODIS AODdata sets is better than the other one everywhere. However, ATSR ADV haslimitations over bright surfaces which the MODIS DB was designed for. Toallow for comparison of MODIS C6 results with previous analyses where MODISCollection 5.1 (C5.1) data were used, also the difference between the C6 andC5.1 merged DTDB data sets from MODIS/Terra over China is briefly discussed. The AOD data sets show strong seasonal differences and the seasonal featuresvary with latitude and longitude across China. Two-decadal AOD time series,averaged over all of mainland China, are presented and briefly discussed.Using the 17  years of ATSR data as the basis and MODIS/Terra to followthe temporal evolution in recent years when the environmental satellite Envisat was lost requires acomparison of the data sets for the overlapping period to show theircomplementarity. ATSR precedes the MODIS time series between 1995 and 2000and shows a distinct increase in the AOD over this period. The two dataseries show similar variations during the overlapping period between 2000 and2011, with minima and maxima in the same years. MODIS extends this timeseries beyond the end of the Envisat period in 2012, showing decreasing AOD.

Two decades of satellite observations of AOD over mainland China using ATSR-2, AATSR and MODIS/Terra: data set evaluation and large-scale patterns