Supercooled sulfuric acid solution droplets are a major constituent of the stratospheric background aerosol. We report the rate of homogeneous freezing and the crystallization dynamics of single levitated sulfuric acid solution droplets with 0 to 57.6 wt.% H₂SO₄. The energy of formation of the critical nucleus and the self-diffusion activation energy are deduced from the experiments as a function of temperature and concentration. The results are compared to both theoretical and experimental work of other groups.