RELATIONSHIPS BETWEEN OZONE PHOTOLYSIS RATES AND PEROXY RADICAL CONCENTRATIONS IN CLEAN MARINE AIR OVER THE SOUTHERN-OCEAN

Measurements of the sum of inorganic and organic peroxy radicals (RO2) and photolysis rate coefficients J(NO2) and J((OD)-D-1) have been mad e at Cape Grim, Tasmania in the course of a comprehensive experiment w hich studied photochemistry in the unpolluted marine boundary layer. T he SOAPEX (Southern Ocean Atmospheric Photochemistry Experiment) campa ign included measurements of ozone, peroxides, nitrogen oxides, water vapor, and many other parameters. This first full length paper concern ed with the experiment focuses on the types of relationships observed between peroxy radicals and J(NO2), J((OD)-D-1) and root[J((OD)-D-1)] in different air masses in which ozone is either produced or destroyed by photochemistry. It was found that in baseline air with ozone loss, RO2 was proportional to root[J((OD)-D-1)], whereas in more polluted a ir RO2 was proportional to J((OD)-D-1). Simple algorithms were derived to explain these relationships and also to calculate the concentratio ns of OH radicals in baseline air from the instantaneous RO2 concentra tions. The signal to noise ratio of the peroxy radical measurements wa s up to 10 for 1-min values and much higher than in other previous dep loyments of the instrument in the northern hemisphere, leading to the confident determination of the relationships between RO2 and J((OD)-D- 1) in different conditions. The absolute concentration of RO2 determin ed in these experiments is in some doubt, but this does not affect our conclusions concerned either with the behavior of peroxy radicals wit h changing light levels or with the concentrations of OH calculated fr om RO2. The results provide confidence that the level of understanding of the photochemistry of ozone leading to the production of peroxide via recombination of peroxy radicals in clean air environments is well advanced.