Meridional distributions of NOx, NOy, and other species in the lower stratosphere and upper troposphere during AASE II

The meridional distribution of NO x in the lower stratosphere and upper troposphere is inferred from 10 flights of the NASA DC‐8 in the northern winter of 1992, along with like distributions of NO y , NO x /NO y , CO, and C 2 Cl 4 . In the lowest few km of the stratosphere there is little vertical gradient in NO x over the range of latitudes measured (40°–90°N). There is a substantial latitudinal gradient, with 50 pptv above the pole and 120 pptv near 40°N. In the uppermost few km of the troposphere, background values range from 30 pptv over the pole to 90 pptv near 40°N. On two occasions higher values, up to 140 pptv in the mean, were seen 2–3 km below the tropopause in association with frontal systems. The meridional distributions of CO and C 2 Cl 4 show the same feature, suggesting that the source of the elevated NO x is near the earth's surface.