How a nocturnal cold front amplified wildfire impacts on near-surface air quality downwind of the second largest US wildfire Atmospheric Research

Ongoing global climate change has yielded a myriad of catastrophic weather hazards, including extreme heat, drought, and severe fire weather conditions across global dryland environments. A massive wildfire ignited across the Texas Panhandle between 27 and 28 Feb 2024 (i.e., Smokehouse Creek Fire, the second largest wildfire in the US history), which consumed over 1,000,000 ha of land and resulted in an overall loss of greater than >$1 billion. Understanding aerosol mixing processes and the associated kinematics near the surface and within the nocturnal boundary layer (NBL) during such wildfire events is crucial for various applications, including predicting and monitoring environmental air quality (AQ), weather forecasting and transport and dispersion modeling. This study provides, for the first time, an empirical evidence of how a nocturnal cold front amplified the wildfire impact on AQ at a site located 250 km downwind of the second largest US wildfire, yielding hazardous concentrations of fine particulate matter (PM2.5–250 μg m−3). Using a combination of lidar-derived aerosol backscatter, vertical velocity and horizontal wind profiles, 10 m-tower observations of meteorological parameters, radiosonde-derived thermodynamics, and near-surface PM2.5 measurements, our analyses revealed that narrow and intense updrafts (i.e., vertical velocity of up to 5–10 m s−1) along the leading edge of a nocturnal cold front triggered the entrainment of an elevated smoke plume (∼1500-2000 m above ground) down to the surface via broader and weaker downdrafts (−0.5 to −2.0 m s−1). This helped explain the transport and vertical mixing pathway of the wildfire plume near ground and aloft. Results reported enhance our understanding of NBL processes and provide critical insights for improving AQ forecasting and validating aerosol transport in dispersion models. Grant no. NA21OAR4590361