Ozone destruction and production rates between spring and autumn in the Arctic stratosphere

In situ measurements of radical and long-lived species were made in the low er Arctic stratosphere (18 to 20 km) between spring and early autumn in 199 7. The measurements include O-3, ClO, OH, HO2, NO, NO2, N2O, CO, and overhe ad O-3 A photochemical box model constrained by these and other observation s is used to compute the diurnally averaged destruction and production rate s of O-3 in this region. The rates show a strong dependence on solar exposu re and ambient O-3. Total destruction rates, which reach 19%/month in summe r, reveal the predominant role of NOx and HOx catalytic cycles throughout t he period. Production of O-3 is significant only in midsummer air parcels. A comparison of observed O-3 changes with destruction rates and transport e ffects indicates the predominant role of destruction in spring and an incre ased role of transport by early autumn.