The initial atmospheric corrosion of copper was investigated by means of a quantitative in situ analysis in an atmosphere containing 120 ppb of acetic acid and 95% relative humidity using a quartz crystal microbalance (QCM) integrated with infrared reflection absorption spectroscopy (IRAS). Crystalline cuprous oxide (various structural forms of Cu2O) and hydrated copper acetate were detected as corrosion products during up to 100 h of exposure. The quantification of data was made possible through an observed linear relationship between the absorbance of vibrations (IRAS) of both phases and the corresponding mass (QCM). The quantification of cuprous oxide was further supported by ex situ coulometric reduction of the corrosion products. The growth rate of cuprous oxide was initially very fast but almost zero after 20 h exposure where it reached an average thickness of 13 +/- 1 nm. Copper acetate exhibited a more constant growth rate. Atomic force microscopy showed a uniform growth of cuprous oxide with surface roughness that increased with time and localized formation of copper acetate. The quantified data are consistent with a previously proposed model that involves proton- and acetate-induced dissolution of copper and subsequent precipitation of cuprous oxide and copper acetate. (c) 2007 The Electrochemical Society.