Vertical profiles of NO were measured during the TROPOZ II aircraft campaign in January 1991. Altogether, 30 flights were made along the coastlines of western Europe, eastern North America, South America, and western Africa, covering latitudes between 67 ¿N and 56 ¿S and altitudes between 0 and 11 km. As a result of the general wind pattern, westerly winds at all northern and southern midlatitudes, the NO data show large-scale outflow of NO-polluted air along the east coasts of the North and South American continents and inflow of clean maritime air over the west coasts of South America, North Africa, and Europe. The NO concentrations in the free tropospheric air flowing out from the (winter) North American continent lie between 100 and 300 parts per trillion by volume (pptv) with a weakly C-shaped vertical profile. The air coming off the (summer) South American continent has a factor of 3 lower NO concentrations, between 40 and 100 pptv, but a more pronounced C-shaped vertical profile with NO mixing ratios of up to 200 pptv in the upper troposphere of the tropics. The salient features in the NO distribution are discussed with the help of 3 day back trajectories. ¿ 1997 American Geophysical Union