Wildfire Smoke and COVID-19

A key pollutant in any discussion of wildfire smoke is particulate matter of less than 2.5 microns in thickness, or PM 2.5. It's important to understand this particulate matter in order to understand the effects of wildfire smoke.

Wildfires are unique compared to other sources of air pollution because they burn over an extremely wide area and an extremely wide range of materials, from grasses and foliage to housing. As a result of this, wildfire smoke is a heterogeneous mixture of all sorts of pollutants, including volatile organic compounds, nitrogen oxides, Carbon Monoxide, and particulate matter (PM) of varying sizes. The exact chemical makeup of smoke from a given event can vary dramatically based on a variety of conditions, but PM is almost always present in high concentrations (Kondo et al. 2019).

PM is itself a broad class of pollutants that come from many sources, but the PM in wildfire smoke is usually a product of organic carbon interacting with other chemicals in the atmosphere (Stephens et al. 2009). Particulate matter that is extremely small is an especially concerning class of pollutants that is very common in wildfire smoke. The documented respiratory health effects of particulate matter that is less than 2.5 microns thick (PM 2.5) include decreased immune response, decreased lung function, asthma and respiratory inflammation (Xing et al. 2016).

PM 2.5 is common in wildfire smoke and other forms of pollution such as vehicle emissions, but there is reason to suspect that exposure to wildfire smoke can be more damaging than exposure to sources that contain only or mostly PM 2.5. Research has estimated a 6% increase in asthma-related hospital admissions for each 10 micrograms per cubic meter increase in PM 2.5 from smoke on smoky days. This effect is higher than estimates for increases in typical PM 2.5 mixtures (Henderson 2020).

The question is, does exposure to wildfire smoke amplify coronavirus? Currently, scientists have mixed evidence on whether or not wildfire smoke increases susceptibility to respiratory infections. However, researchers studying the effects of PM 2.5 have pointed out how exposure to the pollutant suppresses the immune system and reduces the capacity of macrophages in the body to deactivate pathogens, leading some to hypothesize that air pollution would be a significant factor amidst the pandemic. With respect to coronavirus, this has been borne out so far, with researchers showing varying levels of increase in relative risk of mortality for increases in total breathable particulate matter, and short term exposure possibly making infections more likely. Studies increasingly indicate that PM 2.5 is bad for coronavirus, likely due to its ability to compromise the immune system (Mehmood et al. 2020).

The effect of wildfire smoke on coronavirus morbidity has not been specifically studied yet, but given that smoke blanketed many parts of the West coast for an extended period during the pandemic it is reasonable to hypothesize that the increased ambient concentrations of PM 2.5 which resulted from the season's wildfires played some role in the severity of the pandemic.

Climate change is the other major factor increasing the frequency and intensity of wildfires (Mueller et al. 2020). As with forest management, the solutions to limiting warming are very well established, but they have yet to be acted upon sufficiently. A recent report by the World Resources Institute highlights that global greenhouse gas emissions would need to be cut in half globally by 2030 and reduced to net zero by 2050 in order to limit global warming to 1.5 degrees Celsius. The report warns that the intense wildfire seasons experienced so far are a result of just 1 degree Celsius of warming, and that with the commitments most nations currently have in place, we are on track for a 3 degrees Celsius increase in global average temperatures (Lebling et al. 2020).

As with forest management, there are clear steps to be taken by governments to address climate change. To list them all would be extremely challenging, but briefly political science academics, activists and some politicians have coalesced around a consensus that involves bundling policies to address climate change with social policy and economic investments to offset the negative side effects of transitioning to a sustainable economy (Bergquist et al. 2020).

The common thread of both of these contributing factors is that the clear solutions are not currently being acted upon. Without a significant shift in public policy, it is likely that exposure to wildfire smoke and its associated health impacts will become increasingly prevalent in the future. In particular, exposure to PM 2.5 in wildfire smoke as a share of total PM 2.5 exposure is likely to increase as industrial sources like power generation and vehicle emissions transition to renewable energy (DeBell 2006). If there is another widespread outbreak of a respiratory virus in the future, whatever outcomes related to wildfire exposure we are currently experiencing may be even more severe.