Refractive indices of aqueous solutions of ammonium sulfate were measured over a wavelength range of 240 to 400 nanometers (nm) at a temperature of 292 K. The solutions examined cover a broad range from the saturation concentration of ammonium sulfate in water at 292 K down to low concentrations. Solutions studied were: 42.5, 30.4, 23.6, 16.3, 8.5 weight per cent ammonium sulfate. Optical field measurements of these aerosols require knowing the necessary optical constants, and these constants in the ultraviolet (UV) are given here. Our results were found to be in agreement with literature values at longer wavelengths. Additionally, a Lorentz-Lorenz analysis is presented to extend our results to other wavelengths and temperatures. ¿ 1998 American Geophysical Union