(136b) Formation of Secondary Organic Aerosol From the Direct Photolytic Generation of Organic Radicals

The immense chemical complexity of organic aerosol, which inhibits predictions of the explicit kinetic behavior of the formation and destruction of these aerosols, is caused primarily by the nearly uncountable number of reactive pathways by which constituent molecules can be oxidized. In this talk, we present a novel method for generating secondary organic aerosol (SOA) by using a photolabile precursor to generate important radical intermediate species directly, for example by photolyzing an iodoalkane to produce alkylperoxy radicals. These radical species, which are the same as those that participate in atmospheric oxidation, react further to form lower-volatility products that subsequently condense onto particles. This method presents two main advantages over standard oxidant-initiated studies: first that subsequent oxidative steps are suppressed in the absence of a gas-phase oxidant, and second that by tailoring the precursor species to have a specified structure, we can examine the effect that the location of the radical site within a molecule has on its ability to form new SOA.  Measurements of yields and chemical composition (by aerosol mass spectrometry with either electron impact or vacuum ultraviolet ionization) allow for the comparison of the aerosol generated using this technique with those from chamber experiments, wherein oxidation is initiated by the hydroxyl radical.