Understanding the Health and Environmental Impacts of Wildfires

Wildland fires are increasingly prevalent events around the world, affecting millions of people through personal displacement and domestic infrastructure destruction; poor air quality with short- and long-term health consequences; and lasting environmental impacts on water supply contamination, food production, and habitat destruction. This increasing frequency and global severity of wildfires is due to changing local and global climate conditions, and human activities related to land use change and wildfire events will continue to cause significant global disruption in the future.

To shine a spotlight on current trends within this crucial topic area, ACS Publications is pleased to share two curated collections of cutting-edge developments published across our Environmental Science journal portfolio. In addition to the open access articles featured in these collections, all articles will be free to read for the next three months in light of this important topic.

Wildland Fires: Emissions, Chemistry, Contamination, Climate, and Human Health

This recently published Special Issue highlights the latest discoveries on the environmental and health impacts of wildland fires. This ongoing rolling collection will continue to update as additional papers complete the peer review process, and we encourage you to periodically revisit the Special Issue page for the latest studies.

Emissions, Chemistry, and the Environmental Impacts of Wildland Fire

This retrospective Collection includes articles from 2019-2024 published in ACS ES&T Air, ACS ES&T Water, Environmental Science & Technology, and Environmental Science & Technology Letters. This Collection showcases the breadth and complexity of wildland fire research, covering wildland fire emissions, impacts on the wildland/urban interface, brown carbon production, the atmospheric evolution of wildland fire smoke, source apportionment studies, impacts on human health and ecosystems, and advances in smoke modeling.

Article Spotlight: The Effects of Wildfire Smoke on Residents of Unburned Homes

Devastating wildfires continue to increase in frequency and intensity around the world, and climate change projections indicate that they will only continue to grow.¹ Globally, 3.9×10⁶ square kilometers of land burned in the 2023–2024 season, generating fire carbon emissions 16% above average.² The ongoing Greater Los Angeles wildfires exemplify this growing crisis, having already burned over 40,000 acres, destroyed more than 12,300 structures, and prompted evacuation orders for nearly 200,000 residents as of January 2025.³ The Palisades Fire and the Eaton Fire, two of the largest blazes, have caused significant destruction and loss of life.

As we look to rebuild, it is necessary to take stock not just of the physical losses, but the potential long-term health effects of wildfire smoke damage, even for residents whose homes have remained standing. Even fighting the fires can come at an environmental cost, and smoke damage can have economic impacts for local businesses.

A December 2024 study published in ACS ES&T Air by Colleen E. Reid and colleagues documents how physical health symptoms and perceptions of air quality have been impacted among residents of smoke-damaged homes.⁴ The data comes from the Marshall Fire, a wildland urban interface fire that destroyed more than 1,000 structures in two Colorado communities in December 2021. Due to high winds, smoke and ash were carried some distance, affecting an unknown number of unburnt buildings. The researchers wanted to gain a better understanding of whether this smoke or ash damage was associated with health impacts for people living in and around the fire zone. Their results suggest an increase in headaches and strange tastes, with rates significantly associated with proximity (within 250 meters of the home) to destroyed buildings.

A sister paper from the team focuses on measurements of volatile organic compounds (VOCs) inside homes impacted by smoke from the Marshall Fire.⁵ These VOCs can be toxic, and they may undergo reactions that form ozone and secondary organic aerosols downwind. In addition to the reported health effects, the authors revealed increased VOC levels in unburnt homes after the fire. These decreased slowly, falling on average to around 20% of the initial post-fire value after five weeks. The composition of these VOCs was described by a combination of biomass burning emissions and indoor air composition.

More research conducted after the Marshall Fire by Jech et al⁶, published earlier in 2024, has demonstrated that fire-affected homes had elevated concentrations of heavy metals, including chromium, copper, lead, and zinc; however, they noted the concentrations were below thresholds of concern, and there was no corresponding increase in concentrations of polycyclic aromatic hydrocarbons⁶—a contaminant released on burning of carbon-based materials that is considered very harmful to human health, and has been linked to reduced lung function, exacerbation of asthma, and increased rates of lung and cardiovascular diseases.⁷

Understanding the spatial and temporal patterns of such exposure and its population impacts is crucial and will require the right tools. Other work, again coming out of Colorado, has looked at two distinct methods to identify trends in summer smoke, nonsmoke, and total PM2.5 (particulate matter with diameters smaller than 2.5 μm) across the US from 2006 to 2016.⁸ Other teams working in this field have developed machine learning models of daily wildfire-driven PM2.5 concentrations using a combination of ground, satellite, and reanalysis data sources⁹—which could ultimately help us to understand the drivers and societal impacts of wildfire smoke.

These detailed follow-ups from wildfires are important, emphasizing that smoke from wildfires is and will continue to be a health risk. Current studies have helped with short-term exposure, but we need more research on longer, repeated exposures to improve public health responses. A January 2025 Perspective article,¹⁰ co-authored by Reid, revisits recent studies and reiterates the need for future research that looks at both longer-term effects and different exposure patterns to better protect public health.

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References

1. Liu, Y. et al. Projection of Future Wildfire Emissions in Western USA under Climate Change: Contributions from Changes in Wildfire, Fuel Loading and Fuel Moisture. Int. J. Wildland Fire 2022, 31 (1), 1–13.
2. Jones, M. W. et al. State of Wildfires 2023–2024. Earth Syst. Sci. Data 2024, 16, 3601–3685.
3. Missions, L. Greater Los Angeles Wildfires - January 2025. U.S. Geological Survey, U.S. Department of the Interior.
4. Reid, C. E. et al. Physical Health Symptoms and Perceptions of Air Quality among Residents of Smoke-Damaged Homes from a Wildland Urban Interface Fire. ACS EST Air 2025, 2, 1, 13–23.
5. Dresser, W. D. et al. Volatile Organic Compounds Inside Homes Impacted by Smoke from the Marshall Fire. ACS EST Air 2025, 2, 1, 4–12.
6. Jech, S. et al. Determination of Soil Contamination at the Wildland-Urban Interface after the 2021 Marshall Fire in Colorado, USA. Environ. Sci. Technol. 2024, 58, 9, 4326–4333.
7. Human health effects of polycyclic aromatic hydrocarbons as ambient air pollutants - Report of the Working Group on Polycyclic Aromatic Hydrocarbons of the Joint Task Force on the Health Aspects of Air Pollution. World Health Organization, 30 November 2021.
8. O’Dell K, et al. Contribution of Wildland-Fire Smoke to US PM2.5 and Its Influence on Recent TrendsClick to copy article link. Environ. Sci. Technol. 2019, 53, 4, 1797–1804.
9. Childs. M. L. et al. Daily Local-Level Estimates of Ambient Wildfire Smoke PM2.5 for the Contiguous US. Environ. Sci. Technol. 2022, 56, 19, 13607–13621.
10. Sacks, J. D. et al. Shifting the Conversation on Wildland Fire Smoke Exposures: More Smoke within and across Years Requires a New Approach to Inform Public Health Action. ACS ES&T Air 2025.