How Humidity Alters Nighttime Smoke Chemistry: New Findings from University of Kentucky

New research from Md. Sohel Rana and Marcelo I. Guzman at the University of Kentucky reveals that relative humidity plays a decisive role in how smoke particles from biomass burning transform after dark. The study focuses on catechol, a phenolic compound commonly released during wildfires and agricultural burning. After sunset, catechol undergoes oxidation, but the chemical pathways it follows depend on the amount of water vapor in the air. Under low humidity, certain reactions dominate, while higher humidity redirects the process toward different products. This matters because nighttime chemistry can change the toxicity, lifetime, and climate impact of smoke aerosols. Communities downwind of fires may face different air quality risks depending on local humidity levels. The findings could improve models that predict smoke behavior and public health guidance. As wildfire seasons intensify, understanding these subtle environmental controls becomes critical for forecasting air pollution and protecting vulnerable populations.