Project at a Glance
Title: Investigation of the effects of atmospheric acidity upon economically significant materials
Principal Investigator / Author(s): Mansfeld, F.
Contractor: University of Southern California
Contract Number: A932-113
Research Program Area: Economic Analysis
Topic Areas: Impacts
A number of materials of economic significance have been exposed at three sites in Southern California (Burbank, Long Beach and Upland) and at a background site in Central California (Salinas) during the time between March 1986 and August 1990. These materials were galvanized steel, nickel, aluminum, two types of flat latex exterior house paint, nylon fabric, polyethylene and concrete. Due to experimental problems with the concrete blocks and difficulties in determining corrosion damage for polyethylene, no experimental corrosion data are available for these two materials. Corrosion damage was determined by weight loss for galvanized steel, nickel, aluminum and the two paints. For the nylon fabric the loss of breaking strength was used as a measure of corrosion damage. Atmospheric data were provided by the California Air Resources Board's air monitoring network at the test sites. Relative humidity data were obtained from local airports.
Corrosion rates were very low at all four locations. For galvanized steel the average corrosion rate was less than 1 mm/year. Such low values are usually observed only for clean, rural areas. Another interesting result is the time dependence of corrosion rates. For galvanized steel, nickel, and aluminum, corrosion rates were higher in the summer than in the winter, which is opposite to the time dependence observed at most other locations worldwide. It is very likely that the time dependence observed in Southern California is due to photochemical produced acids, particularly nitric acid (HNO3), for which concentrations peak during the summer months. However, this conjecture could not be proven because reliable, long-term HNO3 monitoring data were not available for the four test sites during the study.
A multivariate regression analysis of the experimental corrosion and aerometric data showed that the observed corrosion damage could be explained satisfactorily for galvanized steel, nickel, and aluminum using variables related to °3 concentrations and relative humidity. 03 itself is not corrosive, but it is a good indicator of photochemical produced HN03 and perhaps other components of smog that are direct causes of corrosion. Based on the regression equations estimates can be made concerning the reduction of corrosion damage due to the reduction of acidic deposition in California. However, because the relationship of °3 to the underlying, direct agents of corrosion is site specific, the results are valid only for the monitoring sites included in this study and cannot be applied to estimate the cost of materials damage in the South Coast Air Basin or statewide.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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