Threefold reduction of modeled uncertainty in direct radiative effects by constraining absorbing aerosols over biomass burning regions

Absorbing aerosols emitted from biomass burning play an essential role in affecting the radiation balance, cloudiness, and atmospheric circulation over tropical regions. Assessments of these impacts rely heavily on the modeled aerosol absorption from poorly constrained global models and thus exhibit large uncertainties. By combining the AeroCom global model ensemble with satellite and in situ observations, we provide new constraints on the aerosol absorption optical depth (AAOD) over the Amazon and Africa. Our approach enables identifying, for each model, error contributions from emission, lifetime, and MAC (mass absorption coefficient), with emission and MAC dominating the modeled AAOD errors. In addition to primary emissions, we quantify substantial formation of secondary organic aerosols over the Amazon but not over Africa, which potentially contributes to the modeled AAOD errors. Furthermore, we find that discrepancies in the direct aerosol radiative effects between models decrease by threefold after correcting for the identified errors. This demonstrates that our work can significantly reduce the uncertainty in aerosols, which are considered the most uncertain radiative forcing agent.