BOUNDARY-LAYER OZONE DEPLETION AS SEEN IN THE NORWEGIAN ARCTIC IN SPRING

Several years of measurements of ozone, hydrocarbons, sulphate and met eorological parameters from Spitsbergen in the Norwegian Arctic are pr esented. Most of the measurements were taken on the Zeppelin Mountain at an altitude of 474 m a.s.l. The focus is the episodes of ozone depl etion in the lower troposphere in spring, which are studied in a clima tological way. Episodes of very low ozone concentrations are a common feature on the Zeppelin Mountain in spring. The low ozone episodes wer e observed from late March to the beginning of June. When the effect o f transport direction was subtracted, the frequenty of the low ozone e pisodes was found to peak in the beginning of May, possibly reflecting the seasonal cycle in the actual depletion process. Analyses based on trajectory calculations show that most of the episodes occurred when the air masses were transported from W-N. Ozone soundings show that th e ozone depletion may extend from the surface and up to 3-4 km altitud e. The episodes were associated with a cold boundary layer beneath a t hermally stable layer, suppressing mixing with the free troposphere. T he concentration of several individual hydrocarbons was much lower dur ing episodes of low ozone than for the average conditions. The change in concentration ratio between the hydrocarbons was in qualitative agr eement with oxidation of hydrocarbons by Br and Cl atoms rather than b y OH radicals.