Cooperative Institute for Research in Environmental Sciences

Long term variations in springtime Arctic boundary layer ozone depletion events at Barrow, Alaska (1973-2012)

Samuel J. Oltmans (1,2), Joyce M. Harris (2), Laura C. Patrick (1,2), Bryan J. Johnson(2)

(1)CIRES, University of Colorado, Boulder, Colorado (2)NOAA/ESRL, Global Monitoring Division, Boulder, Colorado

Since the discovery in the early 1980s of strong boundary layer ozone depletion in the spring in the Arctic, and its association with the activation of bromine emitted from the ocean, there has been extensive research and modeling aimed at understanding this phenomena. At Barrow, Alaska at the NOAA Observatory where this depletion was first noted there is now a forty year record of surface ozone measurements. Depletion events (hourly ozone mixing ratios <10 ppb) that may last several hours or days are associated with air flow off the Arctic Ocean to the site at Barrow, which is just a few kilometers from the coast. The long term surface ozone measurements at Barrow reveal that in March there has been a dramatic increase in the frequency of the depletion events (numbers of hours with ozone <10 ppb). This change is most pronounced in the second half of the record beginning in the early 1990s. Although April is the month with the greatest frequency of depletion events a similar change has not occurred during April. The likely cause of the increase in March is the changing character of Arctic sea ice. Although overall ice extent has diminished somewhat in March, the dramatic change has been the large reduction in multi-year ice and its replacement with annual (first year) ice. It has been shown that first year ice conditions are more advantageous for producing ozone depletion because of a greater number and extent of fissures in the ice that allow for the accumulation of brine on the ice surface and the subsequent activation of bromine. This significant change in the occurrence of boundary layer ozone events in March may signal a change in atmospheric chemistry in the Arctic that is related to climate change in this sensitive region.