5.1 Atmospheric corrosion of metallic materials is a function of many weather and atmospheric variables. The effect of specific corrodants, such as sulfur dioxide, can accelerate the atmospheric corrosion of metals significantly. It is important to have information available for the level of atmospheric SO₂ when many metals are exposed to the atmosphere in order to determine their susceptibility to corrosion damage during their life time in the atmosphere.

5.2 Volumetric analysis of atmospheric SO₂ concentration carried out on a continuous basis is considered by some investigators as the most reliable method of estimating the effects caused by this gas. However, these methods require sophisticated monitoring devices together with power supplies and other equipment that make them unsuitable for many exposure sites. These methods are beyond the scope of this practice.

5.3 The sulfation plate method provides a simple technique to independently monitor the level of SO₂ in the atmosphere to yield a weighted average result. The lead peroxide cylinder is similar technique that produces comparable results, and the results are more sensitive to low levels of SO₂.

5.4 Sulfation plate or lead peroxide cylinder results may be used to characterize atmospheric corrosion test sites regarding the effective average level of SO₂ in the atmosphere at these locations.

5.5 Either sulfation plate or lead peroxide cylinder testing is useful in determining microclimate, seasonal, and long term variations in the effective average level of SO₂.

5.6 The results of these sulfur dioxide deposition rate tests may be used in correlations of atmospheric corrosion rates with atmospheric data to determine the sensitivity of the corrosion rate to SO₂ level.

5.7 The sulfur dioxide monitoring methods may also be used with other methods, such as Practice G84 for measuring time of wetness and Test Method G140 for atmospheric chloride deposition, to characterize the atmosphere at sites where buildings or other construction is planned in order to determine the extent of protective measures required for metallic materials.