A supernova within a distance of about 100 pc from the Earth would increase the cosmic ray flux and thereby the atmospheric ionization. We study the impact of high ion concentrations on aerosol nucleation through experiments. The measurements show that nucleation increases by up to an order of magnitude when the ionization increases from background to supernova levels under fixed concentrations of the nucleating gas. This suggests that a supernova could influence the atmospheric microphysics.