We present parametrized equations for calculation of sulfuric acid/water critical nucleus compositions and homogeneous nucleation rates. The parameterizations are in agreement with the thermodynamically consistent version of classical binary homogeneous nucleation theory <Wilemski, 1984> incorporating the hydration effect. The new parameterizations produce nucleation rates that differ by several orders of magnitude from the rates predicted by other parameterizations available in the literature. Model simulations of atmospheric aerosol formation show that the use of the new parameterizations may in some cases result in simulated nucleation mode particle number densities that are by a factor of 1000 lower than those obtained using the old parameterizations. ¿ 1998 American Geophysical Union