Unique inorganic surface nitrate species are known to be formed by the reactions of alkali halides such as solid NaCl with gaseous NO2, HNO3, and N2O5. We report here that these surface nitrate species do not give nitrite ions upon UV photolysis, unlike stable crystalline inorganic nitrates such as NaNO3. No infrared active products are detected in the salt while the surface nitrate photodecomposes, demonstrating that the surface nitrate species has a unique photochemistry that is distinct from that of crystalline NaNO3. On the other hand, if the surface nitrate is transformed into microcrystallites of NaNO3 through a water-induced surface reorganization, the formation of nitrite is observed upon photolysis, as expected for the stable crystalline salt. A possible mechanism for the decomposition of the surface nitrate involves production of NO2 : NO3surf- + hv --> NO2 + O-surf(-) (8) rather than NO2- + O or ONOO- as observed in earlier studies. The atmospheric implications of these observations are discussed.