Observation of widespread depletion of ozone in the springtime boundary layer of the central Arctic linked to mesoscale synoptic conditions

Recurrent and episodic depletions of ozone (O-3) in the atmospheric boundary layer have been observed at arctic coastal sites during springtime for the past 25 years. Additional measurements from the central Arctic Ocean in April 2003 and 2007 confirm previous observations in 1994 indicating that low (<5 nmol mol(-1)) O-3 levels most likely represent the normal state of the boundary layer of the Arctic Ocean in springtime. Ozone mixing ratios increase sporadically to typical remote background values only during the approach of lows moving northward into the central Arctic from midlatitudes, bringing O-3-rich air into the Arctic basin. During a vast majority of the observed O-3 transitions related to the influence of lows, O-3 mixing ratios are strongly negatively correlated to atmospheric pressure. This negative correlation is generally stronger than the correlation between O-3 mixing ratios and air temperature. The observations indicate that the stable boundary layer, which is a large-scale feature of the Arctic Ocean in springtime, may regularly be void of O-3 implying a shift to halogen radicals as the major oxidizing agent on the same spatial scale. The removal of O-3 in the boundary layer on such a large scale may contribute to a reduction of the warming caused by tropospheric O-3 in the Arctic, although the overall impact on the radiation budget is currently unknown.