ATMOSPHERIC CORROSION EFFECTS OF SO2 AND NO2 - A COMPARISON OF LABORATORY AND FIELD-EXPOSED COPPER

Laboratory exposures of copper have been performed at exposure conditi ons comparable to those in the UN ECE exposure program with respect to air flow conditions, relative humidity, and concentration of the gase ous pollutants sulfur dioxide and nitrogen dioxide. Extrapolation of t he weight increases in the laboratory experiments match well those obt ained at the test sites with high sulfur dioxide and nitrogen dioxide pollution levels. At these sites, sulfate and nitrate were the dominat ing surface constituents, as in the laboratory exposures. Additional c onstituents, detected in the laboratory, but not in the field, were su lfite and nitrite. At test sites with low pollution levels of sulfur d ioxide and nitrogen dioxide, weight increases were much higher than in the laboratory exposures. At these sites, sulfate and nitrate were de tected, but the relative amount of nitrate was much lower compared to the sites with high levels of sulfur dioxide and nitrogen dioxide. How ever, the amount of sulfate was practically the same. In addition, Cu2 O was identified as an important compound at some sites. Characteristi c of all sites with low pollution levels of nitrogen dioxide are the h igh levels of ozone. Ozone was not included in the laboratory experime nts which could explain the discrepancy in weight increase. Laboratory experiments, investigating the combined effects of sulfur dioxide and ozone are presented in another publication. Both chloride and ammonia were detected as surface constituents on all field samples,confirming that salts and/or gaseous pollutants, other than sulfur dioxide, nitr ogen dioxide and ozone, also are important for the understanding of at mospheric copper corrosion. However, the present investigation does no t focus on these pollutants.