UC Irvine

The meridional distribution of NOx 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 NOy, NOx/NOy, CO, and C2Cl4. In the lowest few km of the stratosphere there is little vertical gradient in NOx 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 C2Cl4 show the same feature, suggesting that the source of the elevated NOx is near the earth's surface. Copyright 1994 by the American Geophysical Union.