The role of anthropogenic emissions of NOx on tropospheric ozone over the North Atlantic Ocean: A three-dimensional, global model study

A three-dimensional, global tropospheric model is used to simulate the concentration of ozone over the North Atlantic Ocean over an annual cycle. Two scenarios, a baseline and one in which North American fossil fuel NOx emissions are reduced 50% are simulated. The largest decreases in O3 are found in the summer months closest to the east coast of North America, presumably because of strong photochemical production and transport from the southwest due to the Bermuda High. Ozone decreases are also predicted for other North Atlantic Ocean sites and occur throughout the year, but tend to be smaller than those off North America. The total tropospheric mass of O3 over a region from (2.2S, 82.5W) to (68.8N, 0) decreases by 1.8 Tg O3 from 41.3 to 39.5 Tg O3 when North American NOx fossil fuel emissions are reduced, or roughly 4.4%. Given recent estimates of the export of North American O3 to the global atmosphere, the 50% fossil fuel NOx reduction corresponds to a 30% reduction in the total mass of tropospheric O3 exported from North America to the North Atlantic Ocean. Nonlinearities may be due to the fact that ozone production potential per unit NOx increases as NOx concentrations decrease.