Ozone depletion in the interstitial air of the seasonal snowpack in northern Japan

To examine the behaviour of ozone (O₃) in the seasonal snowpack, measurements were taken of O₃ and CO₂ in the interstitial air on Rishiri Island, which is located in northern Japan, during the 2010/11 winter season. Exhibiting variation on timescales ranging from several minutes to several days, the atmospheric O₃ in the surface air generally increased from December (38 ppb) to April (52 ppb). The ozone mixing ratio sharply decreased below the snow surface. Whereas the CO₂ data in the interstitial air indicated that a rapid exchange between the snow and the atmosphere occurred intermittently, the O₃ mixing ratio remained low and constant (<5 ppb) in the snowpack interior. The vertical profile of the O₃ mixing ratio indicates that the e-folding lifetime of the O₃ loss reaction was 5.0±2.3 minutes during the day and 10.0±6.3 minutes at night, suggesting photochemical O₃ depletion occurred during the daytime. Kinetic experiments using ambient (maritime) air and snow indicate that the photochemical O₃ loss is proportional to the solar radiation and that the O₃ loss rate decreases as dawn approaches during the night. The result of the kinetic experiments using artificial O₃ in the pure air and snow suggests the important role of gaseous species in the ambient air towards O₃ depletion.