Knowledge of the behavior of nitric acid on the surface of ice is important to predicting nitrate loads from snowpacks and determining paleoclimates from ice cores. Our experiments have shown that HNO3 will diffuse across the ice driven by concentration gradients. A diffusion constant, D, for this process was determined from Fick's first law to be 3.5(¿1.0)¿10-7 cm2/sec between -20¿ and -25 ¿C. ¿ 1999 American Geophysical Union