In the United States some spent nuclear fuel is stored in dry cask storage systems. Most dry storage systems use canisters fabricated from austenitic stainless steel. Canisters are exposed to the ambient atmosphere and literature data indicate that near regions of industrial commercial or agricultural activities abundant airborne particulates may include sulfate nitrate and ammonium as well as a smaller amount of chloride. This study evaluated the stress corrosion cracking (SCC) susceptibility of as-received and sensitized Type 304 stainless steel exposed to ammonium nitrate mixed with sodium chloride salts. SCC tests were conducted at 45 °C-44% relative humidity using U-bend specimens coated with salt mixtures of ammonium nitrate and sodium chloride with mole ratios of 3 and 6. After a period of exposure of 1.5 months examination of specimens showed that severe SCC occurred. The SCC severity is higher at the higher chloride concentration. No SCC was observed on specimens exposed only to ammonium nitrate. The results indicate that chloride has a large effect on SCC initiation and nitrate did not inhibit SCC at the tested nitrate to chloride concentration ratios.