Laboratory exposure experiments demonstrate that carbonyl sulfide in wet air corrodes copper at 22⁰C at a rate that is approximately linear with total exposure (the product of exposure time and carbonyl sulfide concentration). The corrosion rate is similar to hydrogen sulfide, a widely recognized corrodant. The much greater average atmospheric abundance of carbonyl sulfide compared with that of hydrogen sulfide or sulfur dioxide suggests that carbonyl suffide may be a major agent of atmospheric corrosion.