Wildfire as a Source of Environmentally Persistent Free Radicals and Reactive Oxygen Species
Ting Fang, Brian Hwang, SUKRITI KAPUR, Katherine Hopstock, Jinlai Wei, Sergey Nizkorodov, Manabu Shiraiwa,
University of California, Irvine Abstract Number: 112
Working Group: Biomass Combustion: Outdoor/Indoor Transport and Indoor Air Quality
AbstractIncrease in wildfires in recent years due to climate change has put human population at growing risk as wildfire emits particulate matter (PM) that can cause reactive oxygen species (ROS) generation and oxidative stress. We collected size-segregated PM samples in California during two wildfire events and at highway and urban sites without wildfires. Environmentally persistent free radicals (EPFRs) are present predominantly on submicron particles (PM
1, aerodynamic diameter ≤ 1 µm) with a minor fraction in PM
1-10, likely semiquinone radicals absorbed on fine-mode soot particles or stabilized by coarse-mode tire/brake transition metals. In water, highway/urban PM form mainly hydroxyl (OH·, 84-88%) and carbon-centered (R·, 12-16%) radicals, whereas R· accounts for a major fraction (~50%) with contributions from superoxide/ hydroperoxyl (·O
2-/·HO
2) and oxygen-centered (OR·) radicals in wildfire PM. Total dithiothreitol activities (OP-DTT) were found to be high in wildfire PM
1, consistent with submicron organics emission from biomass burning. Interestingly, OP-DTT of highway/urban samples are correlated with ROS generation (Hwang et al., ACSESC 2021), while no correlation is observed in wildfire samples, suggesting that OP-DTT might not be a good metric for ROS generation and toxicity in biomass burning aerosols. Combustion condition plays an important role that flaming generates more radicals and higher OP-DTT than smoldering or pyrolysis.