This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: As wildfire smoke plumes travel thousands of miles, sunlight and atmospheric chemistry bleach their color, strip away their campfire aroma and add them to the mix of urban smog. Smoky skies plagued the East Coast and Midwest again in summer 2026, as wildfires hundreds of miles away forced people to cancel sports practices and run air conditioners around the clock.
Living in the western U.S., I am no stranger to this scene. Wildfires and the thick smoke they produce have become a fixture of summer life here. I also study wildfire smoke as an atmospheric chemist, in particular how the smoke evolves as it moves downwind from the flames to the communities where people breathe it.
To understand what's in the smoke you might be breathing, you have to look at where it's been. When a forest burns, the wildfire emits large amounts of fine particulate matter, or PM2.5, along with nitrogen oxides and volatile organic compounds, or VOCs. The compounds and particles emitted by wildfires can harm human health, including the lungs, heart and organs, and include known carcinogens.
How this potent mix of pollutants transforms over time and distance is a complex puzzle. At the NOAA Chemical Sciences Laboratory, our team tracks this behavior, from studying controlled fuel burns in the lab to flying research aircraft through wildfire smoke plumes. Understanding how wildfire smoke ages is essential for predicting its impacts on human health.
The story of smoke begins with how the wildfire burns. High-temperature wildfires behave very differently from cool, smoldering wildfires. Hot, intense flames produce nitrogen oxides, which can harm a person's respiratory system and contribute to the formation of secondary pollutants and reactive carbon compounds like aromatic hydrocarbons, which can increase the risk of certain cancers with long-term exposure.
They also emit smaller amounts of nitrous acid, hydrogen cyanide and isocyanic acid, all of which can be toxic to humans. In contrast, lower-temperature smoldering wildfires release a different mix of compounds, but it is still enriched with toxic aromatic oxygenates and ammonia, which can irritate the respiratory system. This isn't to say that these wildfire emissions are safer for human health, but rather that burning conditions dictate the chemical makeup of the smoke and its subsequent chemical fate.
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