AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Formation of Reactive Oxygen Species by Secondary Organic Aerosols in Water
MANABU SHIRAIWA, Haijie Tong, Andrea Arangio, Thomas Berkemeier, William Brune, Pascale Lakey, Ulrich Poeschl, Joanna Socorro, MPIC
Abstract Number: 183 Working Group: Aerosol Chemistry
Abstract Reactive oxygen species (ROS) exist widely in the atmospheric environment. They play multifunctional roles in atmospheric chemistry, influencing formation and chemical aging of organic aerosols and adverse health effects of particulate matter in air pollution. However, little is known on abundance of ROS within atmospheric aerosol particles.
We detect and quantify ROS and related free radicals in ambient particles and laboratory-generated secondary organic aerosols (SOA). Ambient particles have been sampled with a 24 h time resolution using a rotatory multi-stage cascade impactor in Mainz, Germany. SOA were formed by oxidation of monoterpenes, isoprene, and naphthalene in a 2 m long quartz flow tube reactor and the Potential Aerosol Mass (PAM) chamber. The collected particles were analyzed using a continuous wave Electron Paramagnetic Resonance (CW-EPR) spectrometer. We found that ambient particles with diameter of 100 - 300 nm contain substantial amount of organic radicals with concentrations on the order of 1e10 - 1e12 spin/μg of particles. We show that ambient and laboratory-generated SOA form substantial amounts of ROS including H2O2, OH, superoxide, and other organic radicals upon interaction with liquid water. Formation of OH radicals can be explained by the decomposition of organic hydroperoxides. The molar OH yield from SOA is enhanced in the presence of Fe2+ ions due to Fenton-like reactions. Our findings imply that the chemical reactivity and aging of SOA particles is strongly enhanced upon interaction with water and iron. In cloud droplets under dark conditions, SOA decomposition can compete with the classical H2O2 Fenton reaction as the source of OH radicals. Also in the human respiratory tract, the inhalation and deposition of SOA particles may lead to a substantial release of ROS, which may contribute to oxidative stress and play an important role in the adverse health effects of atmospheric aerosols.