Wildfire smoke causes more air pollution than current atmospheric models can predict. A new study published in the journal Science Advances has revealed the hidden chemistry that explains why.
The study, conducted by researchers at King Abdullah University of Science and Technology (KAUST) and the Chinese Academy of Sciences, found that under sunlight, wildfire smoke particles act as tiny chemical factories, producing harmful oxidants such as peroxides, a group of highly reactive pollutants that contribute to smog and haze.
According to a press release issued by the KAUST, the findings help explain why field measurements consistently detect elevated peroxide levels during wildfire events, even in cities where the normal gas-phase chemical routes that create them should be blocked by other pollutants such as nitric oxide, a common gas produced by burning fuel.
Dean of the Physical Science and Engineering Division at KAUST Professor Chak Chan said the study shows how smoke particles can bypass traditional suppression by nitrogen oxides in polluted environments by generating oxidants internally under sunlight. “This particle-driven pathway is surprisingly efficient and faster than what classical pathways can supply,” he said.
He emphasized the importance of updating atmospheric models, which is essential for communities, including Saudi Arabia, to better anticipate the health risks and environmental impacts of global warming.
The release added that the research team discovered that colored organic molecules in biomass-burning aerosols act as photosensitizers. When they absorb sunlight, they enter excited states that trigger rapid chains of reactions, producing peroxy radicals and then peroxides inside the particles.
Peroxides are not greenhouse gases, but they influence atmospheric chemistry in ways that drive haze, secondary particle formation, and respiratory risks. By acting as radical reservoirs, they also affect broader climate and air-quality dynamics.
The findings reveal how wildfire smoke can drive the formation of secondary particulate matter in addition to being a direct source of particulate matter—a major component of urban air pollution.
Wildfires have quadrupled in size in parts of the western United States since the 1980s, while Mediterranean burn areas have more than doubled in the past two decades. As fires become more frequent and intense worldwide, their smoke is emerging as a hidden source of air pollution on a global scale.
