Springtime boundary layer ozone depletion at Barrow, Alaska: Meteorological influence, year-to-year variation, and long-term change

[1] In April 2008 and March–April 2009 near daily ozonesonde measurements were made over a several week period to study springtime Arctic boundary layer ozone loss in the vicinity of Barrow, Alaska. A detailed picture of the vertical structure of the depletion events from the soundings was obtained showing that the depletion was confined to approximately the lowest 1000 m with an average height of the top of the layer at ∼500 m. The two years were strongly contrasting in the frequency of ozone depletion events providing an opportunity for investigating the differing conditions under which these events develop. Short-term variability of the ozone depletion events is closely tied to the frequency of airflow that is primarily Arctic Ocean in origin (more depletion) or originates at lower latitudes (less depletion). The ubiquitous depletion events are interrupted by periodic mixing of ozone rich air into the boundary layer with the onset of synoptic scale weather changes that interrupt flow from off the Arctic Ocean. A 38-year record of surface ozone measurements at Barrow provides a unique time series that reveals the strong year-to-year variability of ozone depletion event occurrence. During March, but not April or May, there has been a significant increase in the frequency of ozone depletion events. This long-term increase in March depletion events appears to follow the decline in multiyear sea ice in the Arctic Ocean and its replacement by first-year ice. This significant change in the occurrence of boundary layer ozone events in March may signal a change in the oxidative chemistry in the Arctic that is related to climate change in this sensitive region.