Issue Date: February 21, 2011
Long-Lived Oxygen Species Are Key To Ozone Reactions
Atmospheric ozone reacts with polycyclic aromatic hydrocarbons in aerosol particles through a multistep mechanism involving intermediate reactive oxygen species, proposes an international group led by Ulrich Pöschl of Germany’s Max Planck Institute for Chemistry (Nat. Chem., DOI: 10.1038/nchem.988). Researchers have puzzled over O3’s behavior in such reactions, which are of central importance to air quality. Experimental data show surface O3 lifetimes of 0.01 to 10 seconds, but computational studies predict lifetimes of nanoseconds. To reconcile the two, Pöschl and colleagues have devised a new kinetic model in which O3 is first physically adsorbed at a particle surface. From the physically adsorbed state, O3 can desorb back to the gas state, with a desorption lifetime of nanoseconds. Alternatively, O3 can dissociate into O2 and a chemically adsorbed reactive oxygen intermediate with a lifetime of about 100 seconds. The intermediate could be an oxygen atom bound to delocalized π electrons or an alkoxy radical species. The researchers also propose that similar reactive oxygen intermediates play a role in ozone reactions with pollen proteins and with other organic and inorganic material on airborne particles, as well as in the nucleation and growth of new atmospheric aerosols.
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