The first simultaneous measurements of ammonia and nitric acid in the troposphere have been made from an aircraft using a tungsten oxide denuder system. Vertical profiles of NH3 and HNO3 taken over coastal Virginia and Maryland in March and September, 1983, at altitudes from 150 m to 3000 m, show mixing ratios that decrease with altitude. Ammonia profiles show substantial seasonal variation, while nitric acid profiles do not. Using the measured profiles, we calculate, with a one-dimensional photochemical model, lifetimes due to heterogeneous loss of 1 day for HNO3 and 10 days for NH3. In contrast, NH3 profiles up to 5300 m over the North Atlantic ocean during August, 1982 show mixing ratios that increase slightly with altitude. These data represent the first ammonia profiles measured over the ocean. We suggest that the increase in NH3 with altitude is a result of an ammonia-rich continental air mass advected over the ocean followed by the dissolution of NH3 in the marine boundary layer on water-covered sea salt particles.