The solubility of acetone in low-temperature sulfuric acid solutions was studied in a low-pressure Knudsen cell reactor. The time dependence of the uptake coefficient was analyzed to give effective Henry's law coefficients for acetone in 48--68 wt% sulfuric acid solutions between 210 and 240 K. The measured solubilities suggest that very little acetone will be partitioned into sulfate aerosol particles in the upper troposphere. Addition of ammonium sulfate to the sulfuric acid reduced the solubility slightly. No evidence was observed for reaction of dissolved acetone with itself or with nitric acid under the conditions of these experiments. ¿ 1999 American Geophysical Union