Article mis en ligne le 15/02/2022

The absorption of aerosols, although being a key property in estimating their radiative impacts, is not sufficiently constrained in current climate models. The latter also have difficulty in correctly representing the load of aerosols transported above clouds.

This study, dedicated to biomass burning particles plumes transported above clouds over the southeast Atlantic region, made it possible for the first time to accurately model the loads and absorption properties of this type of aerosols. We combined the simulations of the WRF-Chem coupled meteorology-chemistry model with the innovative satellite aerosol retrievals provided by POLDER-3. This approach made it possible to better constrain aerosol properties, both in clear skies above their emission sources areas and during their transport above clouds.

As shown in Figure 1, this modeling exercise resulted in an average above-cloud aerosol optical depth (ACAOD) simulated by WRF-Chem in its optimized configuration for the month of July 2008 (0.48) in good agreement with the POLDER-3 satellite retrievals (AERO-AC algorithm, 0.46 ± 0.09) at 550 nm, indicating a correct representation of the biomass burning particles quantities transported above clouds over the southeast Atlantic Ocean. The absorption of this plume is also satisfyingly simulated by WRF-Chem, with an average value of above- cloud single scattering albedo (ACSSA) of 0.84, very close to that retrieved by POLDER-3 (0.85 ± 0.05) at 550 nm.

The obtained results also provide, thanks to the new constraints brought by the spectral retrievals of the aerosol absorption provided by POLDER-3, an estimate of the proportion of brown carbon (i.e., the absorbing fraction of organic compounds) of the order of 2 to 3 % in this biomass burning aerosol plume.

Article :
Siméon, A., Waquet, F., Péré, J.-C., Ducos, F., Thieuleux, F., Peers, F., Turquety, S., and Chiapello, I.: Combining POLDER-3 satellite observations and WRF-Chem numerical simulations to derive biomass burning aerosol properties over the southeast Atlantic region, Atmos. Chem. Phys., 21, 17775–17805, https://doi.org/10.5194/acp-21-17775-2021, 2021.

Figure 1: Comparison of monthly averaged above-cloud aerosol optical depth (ACAOD, a, b) and above-cloud single scattering albedo (ACSSA, d, e) at 550 nm retrieved by POLDER-3/AERO-AC (a, d) and simulated with the WRF- Chem optimized configuration (b, e) over the southeast Atlantic region for July 2008, with the associated histograms of differences between the model and the satellite observations over the whole domain (c, f). The black frames (0–15° E, 15–5° S) represent the area of study.