Various weather factors are assessed in relation to corrosion of metals. Published data are discussed and new results presented to show that time-of-wetness is a very important factor and that reasonable values may be obtained from analysis of meteorological records. These are applicable for predicting long-range corrosion effects. For short-term corrosion, data must be collected for the particular exposure conditions. Results are presented to show the effect of orientation on time-of wetness, and recommendations are made for increasing this type of study. A summary of data on pollution by SO2 in major cities of Canada is presented and the distribution in Metro Toronto given. It indicates that pollution by SO2 has been decreasing in many areas of the world. The effects on corrosion of chlorides, corrosion products, and temperature are also discussed.