Controlled OH radical production via ozone-alkene reactions for use in aerosol aging studies.

We present a novel method for continuous, stable OH radical production for use in smog chamber studies, especially those focused on organic aerosol aging. Our source produces OH radicals from the reaction of 2,3-dimethyl-2-butene and ozone and is unique as a method that requires neither NOx nor UV photolysis of a radical precursor. Typical radical concentrations are in the range of (4-8) x 10(6) molec cm(-3) and are easily sustainable over experimental time scales of several hours. We discuss design considerations, radical production capability under different operating conditions, and the core source chemistry. As a proof of concept we present preliminary results from oxidation of n-hexacosane aerosol observed with an Aerodyne Aerosol Mass Spectrometer. The extent of hexacosane oxidation is sufficient to significantly change the organic aerosol mass spectrum by virtue of fast heterogeneous uptake of OH radicals at the particle surface, with a calculated uptake coefficient gamma = 1.04 +/-0.21.