Ozone in the Marine Boundary Layer at Cape Grim: Model Simulation

A photochemical box model has been used to simulate the mixing ratio ofozone under conditions reflecting those encountered in the marine boundarylayer at Cape Grim, Tasmania, where a decade-long record of ozone mixingratio is available. The model is based on the proposition that ozone loss byphotolysis, atmospheric reaction with hydroperoxy and hydroxyl radicals, andsurface deposition is balanced by ozone gain via entrainment from the lowerfree troposphere with a small additional source in summer from photolysis ofnitrogen dioxide. This model simulates very well the observed ozone records,reproducing both the small diurnal cycle in ozone mixing ratio observedduring the summer months, and the factor of two seasonal ozone cycle showinga distinct winter maximum and summer minimum. The model result confirms thatunder the low-NO_x conditions of the clean marine boundarylayer net photochemical loss of ozone occurs at all times of year.