Wildfire influence on recent US pollution trends

Abstract

Steady improvements in ambient air quality in the US over the past several decades have led to large public health benefits. However, recent trends in PM2.5 concentrations, a key pollutant, have stagnated or begun to reverse throughout much of the US. We quantify the contribution of wildfire smoke to these trends and find that since 2016, wildfire smoke has significantly slowed or reversed previous improvements in average annual PM2.5 concentrations in two-thirds of US states, eroding 23% of previous gains on average in those states (equivalent to 3.6 years of air quality progress) and over 50% in multiple western states. Smoke influence on trends in extreme PM2.5 concentrations is detectable by 2010, but remains concentrated primarily in western states. Wildfire-driven increases in ambient PM2.5 concentrations are unregulated under current air pollution law, and, absent additional intervention, wildfire's contribution to regional and national air quality trends is likely to grow as the climate continues to warm.

Quantifying fire-specific smoke severity

“…We find that all counties in the Western US (414 counties) experienced an increase in the proportion of total PM 2.5 from out-of-county fire sources (Figure 4B). This finding aligns with recent literature suggesting a reversal of trends in overall air pollution due to wildfire smoke 7,27,28 and links these reversals to transboundary out-of-county fire sources. In the later period, we calculate that for 120 counties, over a quarter of the total PM 2.5 in that county was from trans-county smoke sources (there were no such counties in the early period) and in 3 counties, over half of total PM 2.5 was from trans-county sources.…”

“…48 As the climate continues to warm and wildfires increase across much of the Western US and beyond, 1,49 particulate matter air pollution from these events is trending upward and expected to worsen in the coming decades. [5][6][7]50 A growing literature finds that exposure to wildfire smoke results in a range of negative societal impacts, including impacts on respiratory-related morbidity and all-cause mortality, 44,51,52 interrupted learning, 10,53 and decreased labor productivity. 54 Our work provides a method to connect these smoke PM 2.5 impacts back to specific source fires, and can help clarify policy options that aim to better allocate resources to address this growing envi-ronmental challenge.…”

“…[1][2][3][4] While total PM 2.5 has been improving in the decades since the Clean Air Act, recent evidence suggests that wildfire smoke PM 2.5 has begun to reverse this trend, especially in the Western United States. [5][6][7] This reversal is concerning as recent research suggests that PM 2.5 from wildfire smoke could be more toxic than PM 2.5 from other sources, 4 and that existing air quality regulation is poorly equipped to regulate smoke from wildfires. 7 Smoke PM 2.5 concentrations have now been well measured at broad temporal and spatial scales in the US, 6 and increasing concentrations have been linked to an array of negative societal outcomes, including premature deaths, 8 preterm births, 9 and lower test performance in school-aged children, 10 underscoring the growing social costs of wildfire smoke PM 2.5 exposure.…”