Black carbon (BC) and brown carbon (BrC) are light-absorbing aerosols with significant climate impacts, but their absorption properties and direct radiative effect (DRE) remain uncertain. We simulated BC and BrC absorption during the intense Canadian boreal wildfires in June 2023 using an enhanced version of CHIMERE model. The study focused on a domain extending from North America to Eastern Europe, including a significant portion of the Arctic up to 85°N.

The enhanced model includes an updated treatment for the BC absorption enhancement and a BrC ageing scheme accounting for both browning and blanching through oxidation. When compared to observations, the updated model accurately captured aerosol optical depth (AOD) at multiple wavelengths, both near the wildfires and during transoceanic transport to Europe. Improvements were observed in the simulation of absorbing aerosol optical depth (AAOD) compared to the control model.

The all-sky regional direct radiative effect (DRE) for June 2023 attributed to the intense Canadian wildfires, was reduced from -2.1 W/m² in the control model to -1.9 W/m² (-2.0/-1.8 W/m², ±5%), in the enhanced model, indicating an additional warming effect of +0.2 W/m² (about +10%) due to advanced schemes used for the BC and BrC absorption.

The results indicate the importance of an accurate simulation of aerosol absorption in regional climate predictions, especially during large-scale biomass burning events. They also suggest that traditional models could overestimate the cooling effect of boreal wildfires, highlighting the need for improvement of aerosol parameterization to better predict the DRE and develop effective mitigation strategies.