NASA - National Aeronautics and Space Administration

We present a novel passive satellite remote sensing approach for observing the three-dimensional 22 distribution of aerosols emitted from wildfires. This method, called AEROS5P, retrieves vertical profiles of aer- 23 osol extinction from cloud-free measurements of the TROPOMI satellite sensor onboard the Sentinel 5 Precursor 24 mission. It uses a Tikhonov-Phillips regularization which iteratively fits near-infrared and visible selected re- 25 flectances to simultaneously adjust the vertical distribution and abundance of aerosols. The information on the 26 altitude of the aerosol layers is provided by TROPOMI measurements of the reflectance spectra at the oxygen 27 A-band near 760 nm. In the present paper, we use this new approach for observing the daily evolution of the 28 three-dimensional distribution of biomass burning aerosols emitted by Australian wildfires on 20-24 December 29 2019. Aerosol optical depths (AOD) derived by vertical integration of the aerosol extinction profiles retrieved 30 by AEROS5P are compared with MODIS, VIIRS and AERONET coincident observations. They show a good 31 agreement in the horizontal distribution of biomass burning aerosols, with a correlation coefficient of 0.87 and 32 a mean absolute error of 0.2 with respect to VIIRS. Moderately lower correlations (0.63) are found between AODs 33 from AEROS5P and MODIS, while the range of values for this comparison is less than half of that with respect 34 to VIIRS. A fair agreement is found between coincident transects of vertical profiles of biomass burning aerosols 35 derived from AEROS5P and from the CALIOP spaceborne lidar. The mean altitude of these aerosols derived 36 from these two measurements show a good agreement, with a small mean bias (185 m) and a correlation coeffi- 37 cient of 0.83. Moreover, AEROS5P observations reveal the height of injection of the biomass burning aerosols in 38 3D. The highest injection heights during the period of analysis are coincident with the largest fire radiative 39 power derived from MODIS. Consistency is also found with respect to the vertical stability of the atmosphere. 40 The AEROS5P approach provides retrievals for cloud-free scenes over several regions, although currently lim- 41 ited to situations with a dominating presence of smoke particles. Future developments will also aim at observing 42 other aerosol species. 43