e. In eastern Montana, particulate matter is expected to increase as summer drought increases dust emissions in agricultural areas where land gets tilled for crops (Gage et al. 2016) and tillage is employed as a common summer fallow practice (Cook et al. 2014; Dawson et al. 2014). Wildfires also contribute significantly to high levels of particulate matter, as we discuss in the next subsection.
Separately, but related to air quality concerns, pollen counts in the United States are increasing with projections for doubling by 2040 (Zhang et al. 2015) due to warming temperatures with longer growing seasons (Ziska et al. 2019), and higher atmospheric carbon dioxide levels (Ziska and Caulfield 2000). In addition to worsening seasonal allergies, this increase in pollen poses risks of triggering exacerbations of asthma, which affects 9.1% and 6.8% of Montana adults and children, respectively (MTDPHHS 2013).
Wildfires and wildfire smoke
Between 1997 and 2006, 339,000 human deaths per year globally were attributed to smoke from landscape fires, which includes forest fires, peat fires, grass fires, prescribed burns, agricultural burns, and tropical deforestation burning (Johnston et al. 2012). Deaths and injuries occur to people caught in fast-moving fires, as well as to firefighters, emergency response personnel, and others assisting with fire management. Wildfires can result in large-scale, temporary evacuations, or permanent displacement following the destruction of homes or even entire towns (Insurance Information Institute undated). The 2019/2020 fires in Australia, for example, killed 33 people across the country; in New South Wales alone over 2000 homes were destroyed (BBC News 2020). Closer to home, the November 2018 Paradise Fire in California killed 85 people, displaced hundreds, and destroyed over 18,000 buildings (Vox 2019). Large fires with adverse impacts on communities throughout the western US, including Montana, are increasing as measured in numbers of acres burned (Figure 3-6) because a) climate warming produces longer, drier fire seasons and extensive burning; and b) patterns of human development are increasing human exposure to wildfires (Abotzoglou and Williams 2016; Radeloff et al. 2018).
In Montana, increased fire activity in recent decades has impacted people through an increase in hazardous air quality from wildfire smoke, originating locally or from distant sources (see, for example, Figure 3-6). For the western US, including Montana, warmer and drier conditions during summer have contributed to longer fire seasons and more area burned by wildfires, producing more and longer smoke events (Dennison et al. 2014; Westerling 2016; Dalton et al. 2017). Smoke events in the western US from 2004–2009 were associated with a 7.2% increase in respiratory hospital admissions among adults over 65 yr of age (Liu et al. 2017).
Human response data connecting heat and smoke to human health are limited for Montana. In nearby Boise, Idaho, however, seven of the last ten years have included smoke levels considered “unhealthy for sensitive groups” for at least a week during the fire season (IDDEQ 2013), causing cancellation of some school-related sports activities (Nolte et al. 2018). In 2020, large fast-moving fires in California, Colorado, Oregon, and Wyoming resulted in days with the air quality index rated “hazardous” in locations across the western US.
Air quality hazards from wildfire
Wildfire smoke worsens local air quality (Navarro et al. 2016), with substantial public health impacts in regions with large populations near heavily forested areas (Liu et al. 2015; Reid et al. 2016a; Fann et al. 2018). Smoke decreases visibility causing hazardous conditions (Yue et al. 2013), and can be transported hundreds of miles downwind (Dreessen et al. 2016; Kollanus et al. 2016).
Wildfire smoke contains many components that are hazardous to human health, including particulate matter (more below), polyaromatic hydrocarbons, carbon monoxide, nitrous oxide, aldehydes, benzene, among other components (Reisen et al. 2015; Adetona et al