The aim of this work is to report the results of a study on plain steel exposed for four weeks to acidic fogs. These included two levels of NO - 3 , both alone and in combination with SO 2 - 4 , at 35°C and 90% RH. Gravimetric analysis, XRD, FTIR and polarized light microscopical examinations were used to follow the corrosion effects and the rust trasformations. As a major conclusion, it was found that atmospheric NO x deposited by fogs had no important effect.