Because of the ability of copper to interact with a variety of atmospheric species, and to retain the signatures of those interactions in a stable patina layer, copper is a particularly appropriate material for a study of the rates of corrosion processes. The rate of formation of copper patinas in a specific geographical location is dependent upon the atmospheric concentrations of corrosive species, their degree of interaction with the copper surface, and the mechanisms and rates of the processes that govern interaction. A semi-quantitative model of patina growth is developed for samples exposed for up to several decades to the atmosphere in the greater New York City metropolitan area. In contrast to previous studies of patina chemistry, which have dealt with equilibrium conditions, the present work treats the problem from a kinetic standpoint. Under modern atmospheric circumstances, it is shown that neither the supply of atmospheric water, the supply of incorporated corrosive species from the atmosphere, nor the rate of oxidation chemistry are limiting factors in patina growth. Rather, the growth is controlled by the rate of cementation of patina components at early stages of the growth process, and by the supply of diffusing copper ions at later stages. To assess patina formation on a historical basis, estimates are made of atmospheric and precipitation chemistry in the greater New York City metropolitan area over the past century. The rapid formation of modern patinas, compared with those formed a few decades ago, is shown to be a consequence of increased atmospheric levels of strong inorganic acids, particularly H₂SO₄, perhaps in combination with increased concentrations of atmospheric oxidizing species and organic compounds. -- AATA