OZONE IN THE MARINE BOUNDARY-LAYER AT CAPE-GRIM - MODEL SIMULATION

A photochemical box model has been used to simulate the mixing ratio o f ozone under conditions reflecting those encountered in the marine bo undary layer at Cape Grim, Tasmania, where a decade-long record of ozo ne mixing ratio is available. The model is based on the proposition th at ozone loss by photolysis, atmospheric reaction with hydroperoxy and hydroxyl radicals, and surface deposition is balanced by ozone gain v ia entrainment from the lower free troposphere with a small additional source in summer from photolysis of nitrogen dioxide. This model simu lates very well the observed ozone records, reproducing both the small diurnal cycle in ozone mixing ratio observed during the summer months , and the factor of two seasonal ozone cycle showing a distinct winter maximum and summer minimum. The model result confirms that under the low-NO, conditions of the clean marine boundary layer net photochemica l loss of ozone occurs at all times of year.