Quantifying variability in fire-driven PM2.5 concentrations within Alaska during years of low, moderate, and high fire activity

Wildfire is the dominant disturbance agent in Alaska's forests and tundra. During the years of the highest fire occurrence across the state (2004, 2015, and 2005) wildfires burned over 2.7, 2.1, and 1.9 million ha, respectively. Even within low fire activity seasons (e.g. 2006) fires impact over 100,000 ha of the State of Alaska. During a fire season, which generally lasts between May and September, these fires produce anywhere from 0.094 Mega tons of fine particulate matter (PM2.5) during a low activity fire season (e.g. 2006) to 0.55 Mega tons of PM2.5 during a moderate fire activity season (e.g. 2010) to 2.02 Mega tons of PM2.5 during a high fire activity season (e.g. 2005). While the emissions are spread out over 4-5 month period, in 2005 52% (over 1 Mega ton) of PM2.5 was emitted during a single month. Existing estimates of the impact of wildfire emissions on air quality and subsequent health of population in Alaska is generally limited to urban populations in Anchorage, Fairbanks and Mat-su where direct tower-based measurements of concentrations of PM2.5 are available. However, no estimates of state-wide landscape-scale exposure to fire-driven PM2.5 concentrations has been conducted. The extent, intensity, and longevity of many fire events in Alaska generally exceed those in the continental US thus allowing for repeated prolonged periods of PM2.5 exposure in different regions of the state with individual fire events lasting over 2 months and generating multiple smoke waves across the State as a whole. In this study we examine the patterns of season-long concentrations of PM2.5 emissions across the state during a low (2006), moderate (2010) and high (2005) fire activity seasons across Alaska to assess the variability of fire impacts on air quality both in space and time. Specifically, we quantify the number of days exceeding the 24-hour concentrations of PM2.5 of 35.5 μg/m³, identify regions of pooling PM2.5 concentrations based on prevailing atmospheric circulation patterns, and describe and quantify spatially explicit patterns of occurrence and longevity of smoke waves. We further compare the potential for exposure to unhealthy levels of air pollution resulting from fire emissions for urban, rural, and native communities of Alaska.