NOx‐catalyzed ozone destruction and NOx activation at midlatitudes to high latitudes as the main cause of the spring to fall ozone decline in the northern hemisphere

Recent redeterminations of the rate coefficients for the reaction O + NO 2 → NO + O 2 , the rate‐limiting step in the NO x catalytic ozone destruction cycle, and two rate constants dominating the NO x /NO y ratio, OH + NO 2 (+M) → HNO 3 (+M) and OH + HNO 3 → H 2 O + NO 3 , have the consequence that the decline of total ozone between spring and fall, at midlatitudes to high latitudes, is even more determined by NO x ‐catalyzed ozone destruction than previously calculated. Their use also leads to consistent new conclusions regarding the ozone budget of the stratosphere (and ozone transport to the troposphere). Using UARS Halogen Occultation Experiment satellite data as constraints, we derive model estimates of the ozone budget of the Northern Hemisphere lower stratosphere between spring and fall. Although net chemical ozone production occurs in the latitude region between the subtropical barrier (25°–30°N) and 50°N, total ozone declines in this region because of transport to higher latitudes and to the troposphere. North of 50°N, strong chemical ozone loss leads to total ozone loss as well. The tropical region appears not to play a significant role in seasonal total ozone variation.