Mechanisms for surface ozone depletion and recovery during polar sunrise

As part of the Polar Sunrise Experiment (PSE 94) in April 1994, vertical profiles of ozone concentration, temperature and wind speed above an Arctic Ocean icefloe were obtained to investigate boundary layer ozone depletion. They show sustained periods of depleted surface ozone (<1 ppbv) in a layer 300 to 400 m deep. A one-dimensional model was applied to the data in an attempt to determine the magnitude of chemical destruction rates. The rate of change of ozone corresponding to the combined result of horizontal advection and a volume or a surface sink was calculated to be in the range of -0.001-0.001 ppbv s ^-1 while the surface deposition velocity was estimated, for most cases, to be in the range of 0.006-0.016 cm s ^-1. Generally, at this fixed observational point, air mass changes and associated horizontal advection were dominant factors in controlling ozone change. If weak chemical sink rates are to be separated from strong advection changes, future studies will have to take special care to define the horizontal gradient of ozone.