Adaptation in Real Time: Wildfire Smoke Exposure and Respiratory Health

Wildfires are increasing in frequency, intensity, and area burned worldwide, fueled in part by human-caused climate change(1,2). Wildfire smoke (WFS) plumes, containing a complex mixture of airborne particulates, carbon monoxide and dioxide, nitrogen oxides, volatile organic compounds, and other products of combustion, can travel thousands of miles(3) and pose a threat to human health far from the site of the responsible fire (Figure 1). Fine particulate matter (PM_2.5), a product of combustion processes more generally and present at high concentrations in WFS, is closely linked to health effects. WFS-attributed PM_2.5 concentration is a commonly reported metric of WFS exposure, and in WFS-affected areas frequently exceeds recommended World Health Organization targets by more than 20-fold(4). Indeed, in some areas the rise in airborne particulates attributed to WFS has negated up to 50% of western US policy-related improvements in air quality over the last two decades(5).

Figure 1.

Wildfire in Kelowna, BC, Canada on August 17, 2023 (view from Sutherland Park looking onto the fires that burned along Westside Road in West Kelowna). Photo by Dr Madden Brewster, PhD and post-doctoral fellow at University of British Columbia, Okanagan, BC, Canada. As part of a collaboration with the BC Wildfire Service, Dr Brewster’s postdoctoral research focuses on the cardiorespiratory effects of wildfire smoke in wildland fire fighters.

The short-term, negative health impacts of WFS are widely recognized. There is consistent evidence of association between WFS exposure and acute respiratory health outcomes, including respiratory infections, exacerbations of pre-existing asthma and chronic obstructive pulmonary disease, and related healthcare use(6). WFS exposure is also linked to all-cause mortality, and there is growing evidence for cardiovascular(7) and other health effects(8). Effects are amplified in susceptible populations, including infants and children, pregnant people, the elderly, and those with pre-existing cardiac or respiratory conditions. Evidence is limited regarding the impact of long-term or repeated WFS exposure, potential delayed health effects, and the role of WFS exposure in the pathogenesis of diseases such as asthma or COPD. Urgent investigation of these questions is warranted, as chronic exposure to PM_2.5 from non-WFS pollutant sources has been causally linked to new-onset respiratory and cardiovascular disease, cancer, as well as increased mortality(9).

Some evidence suggests that WFS-attributed PM_2.5 may have exaggerated health impacts compared to other forms of PM_2.5(10,11)_. WFS is enriched with fine particles which have a high relative surface area to adsorb toxicants and chemicals(12). These particles can penetrate deep into the lung during respiration and translocate across the alveolar-capillary barrier, carrying adsorbed products directly into the bloodstream. Current data from in vitro, animal, and human models suggest that PM_2.5 exposure activates inflammation and oxidative stress pathways within the lung and systemically(13); whether and how mechanistic pathways may differ by pollutant source, composition, and co-pollutants is an area of active investigation.

To address health impacts, there is critical need for drastic reduction in global fossil fuel emissions and parallel optimization of forest management. While these objectives are pursued, health interventions aim to limit WFS exposure. Individuals are encouraged to check and respond to their local air quality, primarily via air quality indices released by national public health or environmental agencies and incorporating PM_2.5 data from government monitors (such as the US Air Quality Index and Canadian Air Quality Health Index). When air quality is poor based on these indices, remaining indoors is generally recommended, along with decreasing the indoor infiltration of outdoor air, using high efficiency particle air (HEPA) filtration, and limiting indoor particle-producing activities (such as burning candles). If individuals are unable to make their own environment safe, or if there are other risks to safety (e.g. from co-exposure to extreme heat) they should relocate either to publicly available spaces with cleaner air or to the home of a relative or friend with access to mitigation measures. During travel, individuals should use vehicle air filtration or N-95 respirators to reduce exposure. Aside from exposure mitigation measures such as these, there are no known interventions to prevent or alleviate the biologic impacts of WFS; development of such interventions represents an urgent need.

Effective communication and operationalization of personal exposure reduction strategies is therefore critical. As with any public health measure, education on WFS mitigation requires coordinated effort at multiple levels, balancing consistency of messaging with unique individual needs and community context. Evidence supports a diverse messaging strategy using multiple communication streams and formats to relay consistent, evidence-informed guidance(14). Considerations include point of access (internet, social media, radio, television), content (language, complexity, graphics, resources), and frequency of release and updates. In addition, clinicians and health professionals are trusted sources of information and may provide individualized guidance where possible, and community organizations may also be empowered to complement this role. Individually-tailored strategies may be particularly important for those with higher susceptibility, lower educational attainment, or lack of resources, who would benefit from assistance overcoming barriers to implementing public health recommendations(15).

Indeed, deployment of messaging and resources for optimized health during wildfire smoke events provides an opportunity to directly address health equity. Certain groups are at higher risk of exposure to WFS (vulnerable), including those with occupational exposures (e.g. wildland firefighters, other outdoor workers), individuals living near wildfire-prone regions, and those unable to modify their personal environment to mitigate exposure (e.g. due to housing, resource, or social constraints). Prioritizing engagement with these individuals and communities at higher risk, along with dedication of resources, can help to reduce environmental health disparities. For example, air quality monitors are disproportionately concentrated in urban areas. Efforts to increase the density of air quality monitoring stations in rural and/or underserved regions, many disproportionately impacted by WFS, may improve the ability of communities to check and respond to conditions.

Implementing these actions requires an equitable and nimble approach, with iterative adaptation of efforts to community context, values, preferences, and emerging evidence. Coordinated messaging that makes use of diverse strategies at the individual, community, and population level is needed in parallel to support for ongoing discovery and translation efforts. Success in these endeavors necessitates a cooperative effort among academic, government, industry, and community leaders, with effective communication and knowledge-sharing across sectors. Fortifying resources among the most susceptible and/or vulnerable presents a pathway to environmental health equity and the highest level of health for all.

Key Points.

• Wildfire smoke exposure is a growing threat to global human health.

• The negative, acute respiratory health effects of wildfire smoke exposure are established; potential chronic effects are an area of active investigation.

• Susceptible and/or vulnerable populations must be prioritized for intervention to achieve health equity.

• In addition to addressing the root causes of climate change and optimizing forest management, effective interventions to mitigate personal exposure to wildfire smoke require coordinated efforts and sufficient resource allocation, responsive to individual needs and community context.