Wildfire smoke is usually discussed as an airborne pollutant and a threat to human health. But when smoke and rain coincide, nutrients released by burned landscapes rain back down.
A new study finds that smoke-rain events can deliver large bursts of nitrogen, phosphorus and potassium—three nutrients essential to life—across ecosystems in the United States. As wildfires become more frequent, these nutrient pulses could become an increasingly important, and largely overlooked, ecological consequence of fire.
“It’s important to remember that what goes up must come down,” said lead author Alexandra Ponette-González , urban ecologist at the University of Utah (U) and Natural History Museum of Utah. “There’s so much focus on what goes up and how that affects human health. We’re interested in everything that falls out of the atmosphere and lands on ecosystems, and what that means for our environment.”
Led by researchers at the U, Utah State University (USU) and the Cary Institute of Ecosystem Studies (Cary Institute), the study is the first large-scale analysis to examine how particles in wildfire smoke are delivered to ecosystems through rainfall across hundreds of U.S. sites over multiple years.
Using satellite-derived smoke observations and national network rainfall data, the researchers quantified how often smoke and rain coincided and how much of several nutrients were deposited during those events. Their analysis covered 250 sites across 16 climate regions in 2014, 2020 and 2022.
The results showed many more smoke-rain days in 2022 than in 2014, while regional hotspots shifted from year to year. Although the events were relatively infrequent, they delivered a disproportionately large share of nitrogen, phosphorus and potassium to the study sites.
“Nutrient delivery from air to ecosystems as a result of fossil fuel burning or agriculture can be significant, but the impact of wildfire on rain chemistry has been largely overlooked,” noted coauthor Kathleen Weathers , ecosystem scientist at the Cary Institute.
The study was published on Aug. 25, 2026, in the journal Global Change Biology.
Smoke and rain connect atmosphere to ecosystems
As wildfires burn through landscapes, they consume vegetation and other materials, sending a mix of particles and gases into the atmosphere. Some of that material ends up in rain. When rain falls through the smoke, it washes the particles to the ground in a process known as wet deposition. Once dissolved in water, nutrients from the smoke become immediately available to plants and other organisms.
“You can see the remnants of material that are left behind when the water evaporates,” Ponette-González said. “When rain hits an ecosystem, the nutrients are bioavailable—organisms, whether in lake or on land, can immediately access them because they’re dissolved in water.”
The researchers used data from the National Atmospheric Deposition Program, which began monitoring the chemical composition of rainwater in the 1970s to track acid rain.
Smoke-rain events are becoming more frequent
In 2014, monitoring sites averaged about four days per year when smoke and rain happened at the same time. In 2020, the average was six days. In 2022, the average had increased to about 22 days per year.
The regions experiencing the most smoke-rain events changed from year to year along with the distribution of wildfire smoke across regions of the continental U.S. The Upper Midwest was the top hotspot across all three years, but the regions with the second greatest number of events were the Northern Rockies in 2014, the Southwest in 2020 and the Ohio Valley in 2022.
The variability reflects the interaction between wildfire smoke and precipitation: Smoke can be widespread, but without rain, much of the material will not be deposited through rainfall.
“Smoke plumes are a large source of gases and particles in the atmosphere,” said coauthor Heather Holmes , a chemical engineer at the U. “Understanding the complex interactions between smoke, atmospheric dynamics and precipitation is critical to gain insight on nutrient transport and deposition.”
The researchers also found that smoke-rain events accounted for a disproportionately large share of nutrient deposition over the year. In a high-smoke year such as 2022, smoke-rain days occurred on only about 5% of days but delivered about 20-30% of annual rain-deposited nitrogen, phosphorus and potassium.
More nutrients don’t always mean healthier ecosystems
The authors emphasized that this study did not show that wildfire smoke “fertilizes” ecosystems in a way that necessarily benefits growth or productivity. Rather, it demonstrates that wildfire emissions can be an important source of material deposited into ecosystems. The deposition’s effects depend on the ecosystem receiving it; an added pulse of nitrogen or phosphorus could have different consequences in a nutrient-poor mountain area than in one already receiving abundant nutrients from agriculture or other sources.
In lakes, for example, additional nutrients can increase production and shift community composition. In forests, past research has found that smoke deposition can have both environmentally positive and negative effects in forests, including stimulating tree growth while potentially decreasing survival.
“In general, the atmospheric deposition of nutrients like phosphorus is underappreciated over shorter time scales. Whether that input has a meaningful ecological effect depends on the nutrient status and characteristics of the ecosystem receiving it—we can’t characterize atmospheric deposition as simply ‘good’ or ‘bad,’” said coauthor Janice Brahney , watershed scientist at USU. “With more wildfire and more smoky days, it is increasingly important to understand how much material is being transported in smoke and deposited across the landscape, and what that means for ecosystems.”
First step towards tracing deposits back to individual fires
The authors identified locations where smoke and rain occurred at the same time. Their next step is to trace smoke plumes back to their source and determine how fire characteristics influence the chemistry of depositions. Understanding the connection could help researchers determine if different types of fires—such as forest fires or agricultural burning—contribute different nutrients to different regions.
As wildfire activity and smoke exposure increase, the authors say it is important to expand the conversation beyond what wildfire smoke does while it is in the atmosphere.
“We rely on these ecosystems for food, water, timber and so much more,” Ponette-González said. “This study puts a number on how much wildfire can contribute to nutrient delivery and raises important questions for what that means for ecosystem health.”
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The study’s authors are Alexandra Ponette-González, professor in the Department of City and Metropolitan Planning, University of Utah and curator of urban ecology at the Natural History Museum of Utah; Janice Brahney, associate professor in the Department of Watershed Sciences at Utah State University; Heather Holmes, associate professor in the U’s Department of Chemical Engineering; Bryn Spielvogel, research associate in the U’s Department of Parks, Recreation at Tourism; and Kathleen Weathers, ecosystem scientist at the Cary Institute of Ecosystem Studies.
This work was funded by the U.S. National Science Foundation (DEB 2320976, CBET 2048423, DEB 2213625); the University of Utah Vice President for Research Faculty Small Grant Program; and the Utah Agriculture Experiment Station (UTA01669.)
The study:
Ponette-González, e t. al . Smoke-affected rain fertilizes terrestrial and aquatic ecosystems. Global Change Biology . Aug. 25, 2026. DOI: 10.1111/gcb.71050.
Global Change Biology
Observational study
Not applicable
Smoke-affected rain fertilizes terrestrial and aquatic ecosystems. Global Change Biology
25-Aug-2026