Changes in Ozone Formation Regime Due to Long-Distance Transport of Wildfire Smoke Across North America

In 2023, North America experienced an unprecedented fire season. This caused the widespread dispersal of wildfire pollutants, which could influence ozone formation along the smoke‘s trajectory. Tropospheric ozone (O₃) formation is a complex process influenced by various precursors, including volatile organic compounds (VOCs) and nitrogen oxides (NOₓ). The relationship between these precursors and ozone levels is not straightforward. While VOCs and NOx are key precursors to O₃ formation, their increased concentrations do not always result in higher O₃ levels due to the non-linear nature of O₃ formation. Wildfire smoke introduces a complex mix of VOCs and NOx into the atmosphere, which are carried downwind and can change O₃ formation in both urban and rural areas. The impacts vary depending on whether the region is VOCs-sensitive or NOₓ-sensitive. In this study, we investigate the transport of wildfire-induced O₃ precursors and analyze the complex O₃ sensitivity regimes to assess how wildfire-generated NOx and VOCs contribute to O₃ formation using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). We focus on the period from July 22nd to August 13th, 2023, characterized by numerous wildfires, predominantly originating from the western Canadian region. To validate the model results, we compare our simulation outputs with those generated by the HRRR-Smoke model and the observational data from the Atmospheric Emissions and Reactions Observed from Megacities to Marine Areas (AEROMMA) campaign. This study aims to improve our understanding of the long-range transport and impact of wildfire plumes on atmospheric chemical processes. Additionally, this study provides valuable insights for researchers, public health officials, and policy-makers in addressing the challenges connected to wildfire-induced air pollution.