Changes in wildfire season in Alaska and the consequences for ambient fine PM in recent decades

Recent studies highlight the role of climate change in creating conditions that are increasingly conducive to wildfire activity across large areas of North America. This trend raises significant concerns about the growing impacts of wildfires on regional air quality. In particular, Alaska is warming at an accelerated rate, making it critical to understand how its wildfire seasons are evolving and how these changes influence fire activity and air quality. Fire seasons mark the period each year when wildfires are most likely to occur, and their length and intensity have important implications for management and mitigation efforts aimed at protecting human health in this vulnerable region. By applying temperature thresholds, we find that Alaska's fire season has lengthened by approximately 13.8 days from the early 2000s to recent years, with an average annual increase of 0.81 days. Using fire emissions from the Global Fire Assimilation System (GFAS), we estimate an even greater increase in fire season length—up to 42.33 days—based on recorded fire start and end dates, though this may include non-natural fires. The extension of fire season, as derived from temperature thresholds, has led to an additional 2.09 × 10⁸ kg of PM_2.5 emissions, representing a 3.6% overall increase. To assess the air quality impacts of this lengthened fire season, we use the GEOS-Chem chemical transport model with GFAS fire emissions. Our results reveal that the Alaskan population has been experiencing prolonged exposure to elevated fire-driven PM_2.5 levels each year, with local peaks reaching extreme levels, such as 2036.14 μg/m³ in 2010. The peak fire-driven PM_2.5 concentrations during the extended fire season far exceed the U.S. Environmental Protection Agency (EPA)’s 24-h standard (35 μg/m³), underscoring the escalating air quality and public health risks in Alaska. With global implications for climate, air quality, and public health, this study provides a valuable reference for future wildfire research in fire-prone regions.