The objective of the work reported here was to characterize the tarnish products formed on copper during the early stages of exposure to moist air with trace levels of pollutant gas, in particular hydrogen sulfide and sulfur dioxide/hydrogen sulfide. As determined by x-ray photoelectron spectroscopy and coulometric reduction (chronopotentiometry), the exposure of copper to 50 ppb hydrogen sulfide at 23 degrees C and 70% relative humidity was found to produce a tarnish layer consisting of Cu2O and Cu2S. Addition of 75 ppb sulfur dioxide to a 50 ppb hydrogen sulfide, moist air environment at 23 degrees C and 70% relative humidity encouraged the growth of a thicker tarnish product layer, with proportionally more Cu2O in the Cu2O/Cu2S structure.