A Knudsen cell flow reactor is used to study the uptake of nitric acid by sulfuric acid solutions representative of stratospheric particulate. Henry's law solubility constants are determined using the time dependence of the measured nitric acid uptake efficiencies. Solubilities are reported for sulfuric acid solutions ranging from 58 to 87 weight percent sulfuric acid over a temperature range from 188 to 240 K. In general, the solubility of nitric acid increases with decreasing sulfuric acid concentration and decreasing temperature. Over the reported temperature range the solubilities are cast in the form H*=A exp(B/T), where A=7.47¿10-8 M/atm, B=7.16¿103 K for 58% H2SO4; A=0.202 M/atm, B=3.19¿103 K for 66% H2SO4; A=8.54¿10-3 M/atm, B=3.55¿103 K for 74% H2SO4; and A=3.56¿10-3 M/atm, B=3.32¿103 K for 87% H2SO4. The measured solubilities indicate that nitric acid in the global stratosphere will be found predominantly in the gas phase. The ratio of condensed to gas phase nitric acid is less than 10-4 even under conditions of highly elevated sulfuric acid loading. ¿ American Geophysical Union 1990