Wildfire Smoke: Physical and Chemical Evolution and Impacts

Overview 
Wildfires release vast amounts of smoke that affect air quality, climate, and human health. Our group studies how wildfire aerosols form and change in the atmosphere, focusing on properties like reactivity, viscosity, optical absorption, and their ability to form clouds. We also investigate how sunlight and chemical aging transform these properties over time. 

In the troposphere, we study how smoke influences air quality and climate forcing. In the stratosphere, we examine how major fires, such as those in British Columbia (2017) and Australia (2020), inject smoke that can linger for months and alter ozone chemistry and polar stratospheric clouds. We also investigate tarballs—spherical, high-viscosity, light-absorbing particles formed in wildfires—and determine how they form and influence sunlight absorption. 

Why It Matters 
Wildfire smoke is increasing in frequency and intensity with climate change, yet its properties and evolution remain uncertain. Our research provides data needed to improve models of air quality, climate, and ozone recovery, helping inform health and environmental policy. 

Key Questions or Goals 

• How do wildfire aerosols change as they age in the atmosphere?
• How do these changes affect their impact on air quality and climate?
• What chemical reactions occur on wildfire aerosol in the stratosphere?
• How do tarballs form and influence light absorption? 

Approach / Methods 

• Laboratory studies using oxidative flow reactors and environmental chambers.
• Particle characterization with mass spectrometry, spectroscopy, and electron microscopy.
• Viscosity and phase-state measurements using poke-flow, bead mobility, and FRAP assays.
• Modeling collaborations connecting experimental data to climate and ozone predictions. 

Selected Publications 

• Mahrt, F., et al. (2025). Surprising Crystallinity of Biomass Burning Secondary Organic Aerosol from Catechol and Nitrate Radical Reactions: Evidence and Possible Implications. Environmental Science and Technology, 59(32), 16923–16932.
• Gerrebos, N. G. A., et al. (2025). Two-phase morphology and drastic viscosity changes in biomass burning organic aerosol after hydroxyl radical aging. Environmental Science Atmospheres, 5(12).
• Nikkho, S., et al. (2024). Secondary Organic Aerosol from Biomass Burning Phenolic Compounds and Nitrate Radicals can be Highly Viscous over a Wide Relative Humidity Range. Environmental Science and Technology, 58(49), 21702–21715.
• Gerrebos, N. G. A., et al. (2024). High Viscosity and Two Phases Observed over a Range of Relative Humidities in Biomass Burning Organic Aerosol from Canadian Wildfires. Environmental Science and Technology, 58(49), 21716–21728.
• Schnitzler, E. G., et al. (2022). Rate of atmospheric brown carbon whitening governed by environmental conditions. Proceedings of the National Academy of Sciences of the United States of America, 119(38), e2205610119.

Collaborators / Partners 

• Alex Laskin, Purdue University
• Gregory Vandergrift, Pacific Northwest National Laboratory
• Jay Chang, Pacific Northwest National Laboratory
• Sergey Nizkorodov, University of California, Irvine
• Steve Rogak, University of British Columbia
• Swarup China, Pacific Northwest National Laboratory