Ozone in the marine boundary layer at Cape Grim: Model simulation

Abstract

A photochemical box model has been used to simulate the mixing ratio of ozone under conditions reflecting those encountered in the marine boundary layer at Cape Grim, Tasmania, where a decade-long record of ozone mixing ratio is available. The model is based on the proposition that ozone loss by photolysis, atmospheric reaction with hydroperoxy and hydroxyl radicals, and surface deposition is balanced by ozone gain via entrainment from the lower free troposphere with a small additional source in summer from photolysis of nitrogen dioxide. This model simulates 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(x) conditions of the clean marine boundary layer net photochemical loss of ozone occurs at all times of year.