PEROXY RADICAL CONCENTRATIONS MEASURED AND CALCULATED FROM TRACE GAS MEASUREMENTS IN THE MAUNA-LOA-OBSERVATORY PHOTOCHEMISTRY EXPERIMENT 2

Measurements of peroxy radical concentrations ([HO2] + [RO(2)]) were m ade by the ''chemical amplifier'' technique during the four intensives of the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) a t the Mauna Loa Observatory in 1991-1992. In this study these data are compared with the theoretical values of the peroxy radical concentrat ions obtained from steady state analysis of the complete suite of trac e gas measurements and other relevant parameters also measured during the experiment. The data from 33 days of the study contain time overla p of the concentration and physical data which allow a meaningful theo retical treatment. The experimental results for [HO2] + [RO(2)] agree well with theory for many of the days, but are significantly suppresse d from the theoretical expectations on other days. Two hypotheses are presented and tested to explain the observed suppression. The first in volves the reaction of the peroxy radicals at aerosol surfaces. The se cond proposes the loss of [OH] through its reaction with unknown and u ndetected species to develop peroxy radicals subsequently to which the ''chemical amplifier'' is insensitive. Evidence at hand does not allo w a clear choice between these or possible alternative explanations, T he data suggest that the net rate of O-3 generation in the free tropos phere is about -1.5 parts per billion by volume per day (ppbv d(-1); 2 4-hour average).