Vertical profiles are reported for sulfate, for strong acid-to-sulfate molar ratios, and for related species. Data were obtained in the northeastern United States by airborne filter-pack sampling at multiple altitudes with some concurrent ground measurements and by impactor measurements on the ground and aloft, using semiquantitative FTIR spetroscopic analyses. Filter-pack and impactor approaches were compared during one experimental period. Vertical profile data demonstrate that acid-to-sulfate ratios in ambient aerosols usually increase with altitute (Z) in the lower troposphere, occasionally remain constant with Z, and almost never decrease with Z. The sum of nitrate and nitric acid decreases with Z, but the fraction as nitric acid increases with Z, consistent with the aerosol acidity data. Urban effects on the acid-to-sulfate ratios in aerosols are demonstrated. The results strongly suggests that reequilibration of the aerosol nitric acid-ammonia system must be occurring rapidly and that strong acids (in aerosols and gases) may be available for long-distance transport in the lower troposphere.