Particulate Air Pollution from Wildfires in the Western US under Climate Change

Abstract

Wildfire can impose a direct impact on human health under climate change. While the potential impacts of climate change on wildfires and resulting air pollution have been studied, it is not known who will be most affected by the growing threat of wildfires. Identifying communities that will be most affected will inform development of fire management strategies and disaster preparedness programs. We estimate levels of fine particulate matter (PM_2.5) directly attributable to wildfires in 561 western US counties during fire seasons for the present-day (2004-2009) and future (2046-2051), using a fire prediction model and GEOS-Chem, a 3-D global chemical transport model. Future estimates are obtained under a scenario of moderately increasing greenhouse gases by mid-century. We create a new term "Smoke Wave," defined as ≥2 consecutive days with high wildfire-specific PM_2.5, to describe episodes of high air pollution from wildfires. We develop an interactive map to demonstrate the counties likely to suffer from future high wildfire pollution events. For 2004-2009, on days exceeding regulatory PM_2.5 standards, wildfires contributed an average of 71.3% of total PM_2.5. Under future climate change, we estimate that more than 82 million individuals will experience a 57% and 31% increase in the frequency and intensity, respectively, of Smoke Waves. Northern California, Western Oregon and the Great Plains are likely to suffer the highest exposure to widlfire smoke in the future. Results point to the potential health impacts of increasing wildfire activity on large numbers of people in a warming climate and the need to establish or modify US wildfire management and evacuation programs in high-risk regions. The study also adds to the growing literature arguing that extreme events in a changing climate could have significant consequences for human health.

Keywords: PM2.5; air pollution; climate change; wildfire.

Figure 1

Fraction of PM_2.5 attributable to wildfires by county during fire seasons (May-October) in the present day (2004-2009), on all days (left panel), and on the subset of days that had total PM_2.5 > 35μg/m³ (The National Ambient Air Quality Standards (NAAQS) threshold; right panel).

Figure 2

Difference in smoke wave characteristics in the future (2046-2051) under climate change and in the present day (2004-2009) during fire seasons (May-October). Positive changes (in warm colors) indicate increases under climate change, while negative changes (in cool colors) indicate decreases under climate change. Panels show (a) average intensity of smoke waves; (b) average length of smoke waves; (c) total number of smoke waves during a 6-year period; (d) total number of smoke wave days during the 6-year period; and (e) average length of the smoke wave season.

Figure 3

Fire Smoke Risk Index (FSRI) during fire seasons (May-October). Panel (a) is for present day (2004-2009) and panel (b) is for future (2046-2051) under climate change.

Figure 3

Fire Smoke Risk Index (FSRI) during fire seasons (May-October). Panel (a) is for present day (2004-2009) and panel (b) is for future (2046-2051) under climate change.