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Volume 18, issue 3 | Copyright
Atmos. Chem. Phys., 18, 1573-1592, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Feb 2018

Research article | 05 Feb 2018

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

Gerrit de Leeuw1, Larisa Sogacheva1, Edith Rodriguez1, Konstantinos Kourtidis2, Aristeidis K. Georgoulias2, Georgia Alexandri2, Vassilis Amiridis3, Emmanouil Proestakis3,4, Eleni Marinou3, Yong Xue5, and Ronald van der A6 Gerrit de Leeuw et al.
  • 1Finnish Meteorological Institute (FMI), Climate Research Unit, Helsinki, Finland
  • 2Laboratory of Atmospheric Pollution and Pollution Control Engineering of Atmospheric Pollutants, Department of Environmental Engineering, Democritus University of Thrace, Xanthi, Greece
  • 3National Observatory Athens (NOA), Athens, Greece
  • 4Laboratory of Atmospheric Physics, Department of Physics, University of Patras, Patras, Greece
  • 5Department of Electronics, Computing and Mathematics, College of Engineering and Technology, University of Derby, Derby, UK
  • 6Royal Netherlands Meteorological Institute (KNMI), De Bilt, the Netherlands

Abstract. The retrieval of aerosol properties from satellite observations provides their spatial distribution over a wide area in cloud-free conditions. As such, they complement ground-based measurements by providing information over sparsely instrumented areas, albeit that significant differences may exist in both the type of information obtained and the temporal information from satellite and ground-based observations. In this paper, information from different types of satellite-based instruments is used to provide a 3-D climatology of aerosol properties over mainland China, i.e., vertical profiles of extinction coefficients from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), a lidar flying aboard 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-Track Scanning Radiometer version 2 (ATSR-2), Advanced Along-Track Scanning Radiometer (AATSR) (together referred to as ATSR) and NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Terra satellite, together spanning the period 1995–2015. AOD data are retrieved from ATSR using the ATSR dual view (ADV) v2.31 algorithm, while for MODIS Collection 6 (C6) the AOD data set is used that was obtained from merging the AODs obtained from the dark target (DT) and deep blue (DB) algorithms, further referred to as the DTDB merged AOD product. These data sets are validated and differences are compared using Aerosol Robotic Network (AERONET) version 2 L2.0 AOD data as reference. The results show that, over China, ATSR slightly underestimates the AOD and MODIS slightly overestimates the AOD. Consequently, ATSR AOD is overall lower than that from MODIS, and the difference increases with increasing AOD. The comparison also shows that neither of the ATSR and MODIS AOD data sets is better than the other one everywhere. However, ATSR ADV has limitations over bright surfaces which the MODIS DB was designed for. To allow for comparison of MODIS C6 results with previous analyses where MODIS Collection 5.1 (C5.1) data were used, also the difference between the C6 and C5.1 merged DTDB data sets from MODIS/Terra over China is briefly discussed.

The AOD data sets show strong seasonal differences and the seasonal features vary 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 follow the temporal evolution in recent years when the environmental satellite Envisat was lost requires a comparison of the data sets for the overlapping period to show their complementarity. ATSR precedes the MODIS time series between 1995 and 2000 and shows a distinct increase in the AOD over this period. The two data series show similar variations during the overlapping period between 2000 and 2011, with minima and maxima in the same years. MODIS extends this time series beyond the end of the Envisat period in 2012, showing decreasing AOD.

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Short summary
The complementary use of two sensors, ATSR and MODIS, to provide aerosol information over two decades (1995–2015) is described. To this end, the AOD retrieved from both instruments had to be compared, showing that ATSR slightly underestimates and MODIS overestimates by a similar amount. Results show the increase of aerosols over the years, with an indication of the onset of a decrease in recent years. The AOD spatial distribution shows seasonal variations across China.
The complementary use of two sensors, ATSR and MODIS, to provide aerosol information over two...