Wildfire smoke is not a single, stable substance but a shifting chemical mixture, according to a new review in Reviews of Geophysics. The lead author describes fire plumes as rising columns of hot air, gases, and particles whose composition evolves from the moment of emission. Near the flames, newly released compounds react quickly; farther downwind, they mix with background air and form secondary pollutants such as ozone and secondary organic aerosols. This process, often called plume aging, means that the smoke reaching a community can be chemically different from what left the fire.
The review stresses that plume chemistry depends on multiple factors: what is burning, how intensely it burns, and the atmospheric conditions it encounters. A dense plume injected high into the atmosphere behaves differently from one lingering near the ground. Because these factors interact, even two fires of similar size can produce chemically distinct smoke.
Scientists study plume chemistry using a combination of ground stations, research aircraft, lab combustion experiments, satellites, and atmospheric models. Each method captures a different piece of the evolving system, from real-time gas and particle measurements to offline filter analysis. The authors argue that this integrated understanding is essential for improving air-quality forecasts, assessing health and climate impacts, and informing fire management decisions.