Photolytic radical persistence due to anoxia in viscous aerosol particles

In viscous, organic-rich aerosol particles containing iron, sunlight may induce anoxic conditions that stabilize reactive oxygen species (ROS) and carbon-centered radicals (CCRs). In laboratory experiments, we show mass loss, iron oxidation and radical formation and release from photoactive organic particles containing iron. Our results reveal a range of temperature and relative humidity, including ambient conditions, that control ROS build up and CCR persistence in photochemically active, viscous organic particles. We find that radicals can attain high concentrations, altering aerosol chemistry and exacerbating health hazards of aerosol exposure. Our physicochemical kinetic model confirmed these results, implying that oxygen does not penetrate such particles due to the combined effects of fast reaction and slow diffusion near the particle surface, allowing photochemically-produced radicals to be effectively trapped in an anoxic organic matrix. Sunlight can change the composition of atmospheric aerosol particles, but the mechanisms through which this happens are not well known. Here, the authors show that fast radical reaction and slow diffusion near viscous organic particle surfaces can cause oxygen depletion, radical trapping and humidity dependent oxidation.

Automated summary

Research shows that sunlight can induce stable reactive oxygen species and carbon-centered radicals in organic aerosol particles containing iron. Laboratory experiments demonstrate radical formation, release, as well as iron oxidation and mass loss in photoactive organic particles. The study suggests that fast radical reaction and slow diffusion near viscous organic particle surfaces can lead to oxygen depletion, radical trapping, and humidity-dependent oxidation.