Evaluation of factors which increase corrosion around a mountain summit

Five types of thin films were exposed to the atmosphere at a mountain summit (at an elevation of about 920 m) and on a plain. Short duration exposure tests are more appropriate to measure the impact of deposition of atmospheric pollutants on surfaces than are long duration exposure tests. Short duration exposure tests using thin copper films revealed that corrosion was more intense on a mountain summit than on a nearby plain. The corrosion was mainly caused not by the deposition of particulate SO42−, but rather by the deposition of NO3− ion; SO42− hardly affected the corrosion at all. The concentrations of acidic gases and ion components of aerosols at the mountain summit were found to be less than those at the foot of the mountain. The concentrations of NH3 at the summit were substantially lower than those on the plain. The observations of micro-corrosion morphology on the copper films, the reaction pattern on the reagent films, and the fact that NH3 concentrations at the mountain summit were less than those on the plain suggest that part of the NO3− component deposited at the mountain summit exists as more stable acidic NO3− particles containing less salt particles than those deposited on the plain. In contrast, particulate NO3− deposited on the plain was considered to be neutralized to particles such as NH4NO3 and/or NaNO3.