Infrared emission spectra were measured in the stratosphere at various altitudes and from various zenith angles by means of a balloon-borne Czerny-Turner spectrometer. The equation of radiative transfer was applied to the radiances measured at 11.2μ to yield a concentration profile of HNO3 vapor. The resulting HNO3 concentration profile was characterized by a negligible concentration below 14 km, a maximum concentration of ∼(1.5±0.5)×1010 molecules cm−3 at ∼(19±5) km, and a diminishing concentration above these altitudes. Abstract Infrared emission spectra were measured in the stratosphere at various altitudes and from various zenith angles by means of a balloon-borne Czerny-Turner spectrometer. The equation of radiative transfer was applied to the radiances measured at 11.2μ to yield a concentration profile of HNO3 vapor. The resulting HNO3 concentration profile was characterized by a negligible concentration below 14 km, a maximum concentration of ∼(1.5±0.5)×1010 molecules cm−3 at ∼(19±5) km, and a diminishing concentration above these altitudes.