HO2 OH AND RO(2)/HO2 RATIOS DURING THE TROPOSPHERIC OH PHOTOCHEMISTRYEXPERIMENT - MEASUREMENT AND THEORY/

Ambient concentrations of the hydroxyl (OH), hydroperoxyl (HO2), and t otal peroxy (Sigma RO(2)) radicals were measured as part of the Tropos pheric OH Photochemistry Experiment at Idaho Hill, Colorado, during Au gust and September of 1993. OH radicals were measured using ion-assist ed mass spectroscopy and low-pressure laser-induced fluorescence (LIF) detection techniques. HO2 was measured using; chemical conversion and LIF detection of OH. Sigma RO(2) radicals were measured using a chemi cal amplifier technique, The simultaneous measurements of these key sp ecies provide an opportunity to test our present understanding of the fast photochemistry of the troposphere, Measured HO2/OH ratios were ty pically between 15 and 80, and agreed well with predictions under cond itions where NO mixing ratios were greater than 100 pptv, However, und er clean conditions the measured ratio was a factor of 3-4 lower than predicted. The RO(2)/HO2 ratio was typically a factor of 4-15 larger t han predicted by present theories of tropospheric chemistry, A steady state model was used in an attempt to analyze the discrepancies betwee n the measured HO2/OH and RO(2)/HO2 ratios with present theories of hy drocarbon oxidation in the troposphere.