Aircraft measurements of peroxyacetyl nitrate (PAN) and other important reactive nitrogen species (NO, NO2, HNO3, and NOy) were performed over the continental United States and the eastern Pacific during August-September 1986 at all altitudes between 0 and 6 km as part of CITE 2. PAN measurements were conducted by two independent groups, allowing both intercomparisons and greater confidence in its observed atmospheric structure. PAN was found to be a dominant reactive nitrogen species in the troposphere with 98% of the mixing ratios falling in a range of 5--400 ppt. Typically, the highest mixing ratios (100--300) ppt were observed aloft (4--6 km) with extremely low values (5--20 ppt) in the marine boundary layer. In the lower troposphere. Continental air contained siginficantly more PAN than marine air. The vertical structure of PAN was largely dictated by its thermal destruction rate and equilibrium with available NO2. PAN mixing ratios showed a high degree of variability in both continental and marine atmospheres. Westerly marine air trajectories did not guarantee well-mixed air of uniform composition. Mixing ratios of O3, NOy, NOx, HNO3, C2H6, CO, and CFCl3 were strongly correlated with those of PAN, indicating the important role played by transport processes. High PAN to NOx ratios in the mid-troposphere further support the importance of long-range transport from continental sources. Frequently, descending air masses from the upper troposphere suggested that PAN mixing ratios probably continued to increase above the 6-km ceiling altitude. Air masses with O3<20 ppb, CO<60 ppb, and C2H6<500 ppt contained only miniscule amounts of PAN and are expected to be of tropical origin. Reasons for the observed PAN variability, are discussed. ¿ American Geophysical Union 1990