Thermodynamic attributes of Arctic boundary layer ozone depletion

During spring 2000, a major ozone depletion episode was observed in the boundary layer at Alert, Nunavut, Canada. The ozone in the atmospheric layer extending from the surface to 1500 m was completely removed. This event lasted more than 9 days and was associated with an abrupt transition to an air mass that emanated from the Arctic Ocean. This source region provides the substrates that participate in the chemical reactions leading to ozone removal from the lower atmosphere. After the onset of the ozone depletion episode, the ozone-depleted air mass remained stagnant over the Alert region. In this study, thermodynamic and atmospheric dynamic characteristics of the lower troposphere are examined before, during and after the ozone depletion episode. With these analyses, we evaluate the research hypothesis that extended and regional ozone depletion events require air masses to travel over extensive regions rich in halogens that chemically remove ozone from the lower atmosphere. We establish the links between the atmospheric dynamic and thermodynamic attributes of ozone depletion episodes, chemically active air mass source regions, and locally measured chemistry. Evidence is also provided to show that the principal mechanism to replenish the atmospheric boundary layer with ozone is vertical transport of ozone from aloft down to the lower atmosphere. This transport mechanism is supported by strong wind shear regimes observed aloft.