Large eddy simulations of the Williams Flat Fire: Aqueous chemistry in pyrocumulous clouds

Wildfires are an increasing concern for climate change, air quality and recognized for their substantial impacts on atmospheric composition. In addition to significant emissions of carbon dioxide (CO₂) and particular matter (PM), biomass burning events are characterized by substantial non-CO₂ emissions, which encompass a wide range of species. These emissions significantly influence atmospheric chemistry at a regional to global scale. Particularly in regions with ample fuel sources and hot, dry, or windy meteorological conditions, surface fires can lead to high-intensity crown fires and frequent downwind spotting. In certain circumstances, the intense formation of crown fires triggers the development of pyrocumulonimbus (PyroCb) atop smoke columns, which ascend to the upper troposphere and lower stratosphere (UTLS) and thus promote the dispersion of the fire emissions within wide regions. On August 2, 2019, the Williams Flats Fire ignited due to lightning from early morning thunderstorms in eastern Washington, USA. The main fire activity occurred between August 2 and August 9. On August 8, the high intensity crown fires led to the formation of a PyroCb. This event was observed and probed by the joint NOAA and NASA FIREX-AQ field campaign, providing a unique observation dataset. In this study, we utilize the Weather Research and Forecasting Model (WRF) to assess the impact of the Williams Flats fires on the atmospheric composition. In particular, we couple the representation of detailed multi-phase chemistry (WRF-CHEM) with WRF’s fire spread model (WRF-FIRE), employing WRF’s Large Eddy Simulation capabilities to resolve turbulence at resolutions of 100 m. In this presentation, results from WRF-FIRE-CHEM simulations with and without aqueous-phase chemistry will be shown to isolate its effects on the long-range transport of trace gases and aerosols.