Simulating Regional‐Scale Aerosol Radiative Effects of Wildfire Smoke Using a High‐Resolution Coupled Meteorology‐Chemistry Model: HRRR‐Chem

Abstract Wildfires are increasing in frequency and intensity, strongly influencing both regional air quality and the Earth's radiation budget via their aerosol emissions. Relying on an unparalleled observational data set from the 2019 NOAA/NASA FIREX‐AQ campaign, this study quantifies the direct radiative effects of two wildfires using the HRRR‐Chem. Model predictions agree well with observed aerosol absorption, composition, and mass concentrations in fresh smoke (PM 2.5 > 1,500 μg m −3 ). Our results show pronounced regional direct radiative effects, including daily mean surface cooling exceeding −150 W m −2 and atmospheric warming up to +40 W m −2 in dense plumes. However, our analysis indicates that surface cooling is underestimated in the densest fresh smoke plumes due to aerosol scattering underpredictions. This scattering underestimation is linked to the grid‐scale dilution of dense fresh‐smoke gradients at the 3 km scale, as well as challenges in capturing complex fresh‐smoke particle size distributions using prescribed emission sizes within modal aerosol schemes, emphasizing the need for fire‐specific emission parameters in future biomass burning modeling studies. Furthermore, sensitivity analyses reveal that the volatility of primary organic aerosol is the dominant source of uncertainty in the direct radiative effect (up to 80%), while the optical properties of brown carbon and aerosol mixing state contribute 10%–20% and 5%–15% uncertainty, respectively.