Overview
Wildland fires pose a growing threat to air quality and human health. Fire is a natural part of many landscapes; however, climate change is increasing the extent of area burned and the severity of fires in the United States and many other parts of the world (Jia et al., 2019; Nolte et al., 2018). At the same time, humans have been expanding the “wildland-urban interface” by moving into previously uninhabited areas that may be prone to fire, and forest management has increased fuel loads in many areas. These changes heighten the risk of exposure to fire itself more broadly to fire emissions, which can travel thousands of miles and affect millions of people, creating local, regional, and national air quality and health concerns.
In September 2020, the Board on Atmospheric Sciences and Climate, in collaboration with the Board on Chemical Sciences and Technology, convened a workshop to bring together atmospheric chemistry and health research communities, natural resource managers, and decision makers to discuss current knowledge and needs surrounding how wildland fire emissions affect air quality and human health. Participants also explored opportunities to better bridge these communities to advance the science and improve the production and exchange of information. Definitions of a few key terms used during the workshop are provided in Box 1.
Wildland fire emissions are a complex mixture of chemicals that include particulate matter (PM) and trace gases emitted directly by the fire and those that form later from chemical reactions that occur within the fire plume. There is clear evidence that wildland fire smoke has negative acute health impacts (e.g., Reid et al., 2016; Xi et al., 2020). When PM concentrations are high as a result of smoke, increased mortality is observed. Links to asthma, diabetic outcomes, birth outcomes, and chronic obstructive pulmonary disease (COPD) are established or emerging, and other effects are being explored. Wildland fire smoke disproportionately affects the health of vulnerable populations including children whose lungs are still developing, the elderly, individuals with preexisting conditions, those with occupations that require close proximity to fire and extended time outdoors (e.g., agricultural workers and firefighters), and unhoused populations who may not be able to go indoors to avoid smoke. Currently, much less is known about the chronic effects and repeat exposures to smoke. Many speakers commented on the need to conduct long-term studies to expand knowledge beyond acute health effects.
With more fires occurring within a season and across multiple seasons, the relative amount of exposure to PM ≤ 2.5 micrometers in size (PM2.5) coming from wildland fire smoke is increasing. Exposure periods are also getting longer for individual fire events, heightening the importance of conducting more studies that can capture the types of exposure people are facing. These studies will be difficult and expensive to undertake but will provide much needed information, presenters said.
Throughout the workshop, numerous speakers highlighted the need to answer the following questions: (1) When will smoke arrive? and (2) When will smoke go away? Answers to these questions rely on atmospheric science research and are important for providing actionable information to decision makers and communicating public health risks to communities downwind of wildland fire smoke.
There are a range of tools used to forecast smoke and measure chemicals originating from wildland fire that were discussed at the workshop. At the largest scales, satellite remote sensing, often in combination with modeling, provides information on smoke location and transport used in forecasting. Measurements from aircraft provide important information about the chemical composition of pollutants near fire sources and as smoke travels away, and can also be used with satellite data to better constrain models. Many speakers noted that the complexity of constituents in the smoke, plume dynamics (e.g., vertical plume rise and boundary layer dynamics), smoke movement across complex terrain, and reconciling information across scales are key challenges for which greater understanding could lead to advancements in smoke and air quality forecasting.
Ground-based monitoring networks also serve as important information sources for determining air quality. Numerous workshop speakers commented that the existing monitoring network is useful but too sparse to adequately document wildland fire smoke exposure for many communities. To address this challenge, available low-cost sensors could be distributed more broadly to fill in the gaps. Use of these sensors indoors can also inform actions to mitigate smoke exposure by allowing individuals to directly monitor the air quality where they live and take steps to improve conditions (e.g., keep windows closed or use low-cost box fans with a minimum efficiency reporting value [MERV]-13 filter).
Communicating the risks of wildland fire smoke and how to mitigate those risks requires actionable scientific information, many speakers noted. The public needs answers to questions like “Can children play outside at recess?” “Is it safe to hold an outdoor sporting event?” and “When will smoke be at its worst?” to plan their daily lives while also reducing their exposure. Tools such as the Air Quality Index (AQI) serve as a useful metric for communicating about air quality because it is simple and straightforward, but it may not provide enough information for vulnerable populations and, because of the sparse monitoring network, may not represent the conditions for all who seek guidance on how to react to smoky conditions.
Looking to the future, many speakers noted their expectations that wildland fires will have an increasingly large impact on society. Preparation and continued improvements in the science and communication of risks will likely be essential for reducing exposure and subsequent health impacts. Speakers pointed to research, political will, multidisciplinary collaborations, and robust and sustained funding to support advancement in these areas. There is progress in many aspects of this challenge. For instance, speakers discussed new collaborations that have been developed among federal, state, and local agencies and other
groups to manage lands and develop and disseminate daily information about fire risks. Managers are taking advantage of available tools and information to improve forecasting, and researchers are analyzing data from recent field campaigns. New and soon-to-be-available satellite data are anticipated to provide further insights into the complexity of wildland fires, while also balancing immediate forecasting information needs.
Land management, including prescribed burning often combined with biomass thinning, can reduce the likelihood of catastrophic wildfire risk and associated air quality impacts. While it may be counterintuitive to intentionally set fires to reduce smoke exposure, multiple workshop speakers showed that prescribed burning creates substantially less smoke than wildland fires. Over time, prescribed burns and thinning conducted at regular intervals can keep fuel loads down and help to reduce the occurrence of large wildland fires. A variety of factors make this mitigation strategy challenging. For instance, public acceptance for prescribed burning and the associated smoke exposure can be difficult to obtain, although some speakers noted that this is changing as the public is experiencing longer episodes of wildland fire smoke exposure in recent years and communication about smoke and the value of prescribed fire is improving. More frequent prescribed fires also increase exposure risk to the firefighters assigned to control these burns and additional protections are needed, speakers said. Challenges associated with overcoming political barriers, building necessary partnerships among various groups at local and state levels, and securing the necessary funds for long-term mitigation have slowed implementation of prescribed burns in many areas. California was discussed by some speakers as a state that is prioritizing prescribed burning as a mitigation strategy and addressing the large fuel loads that have resulted from fire suppression over the past century.
While questions remain in both the atmospheric science and health research communities around wildland fire pollutants and health effects, speakers stressed that there is enough information available now to inform actions that will better protect people. Through continued research advancement, collaboration, and expanded communication of risks, the actions needed to lessen wildland fire smoke exposure and impacts on human health may be improved.
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