Atmospheric corrosion of naturally and pre-patinated copper roofs in Singapore and Stockholm - Runoff rates and corrosion product formation

Runoff rates of copper have been determined during a one-year field exposure in the city of Singapore, Republic of Singapore and a four-year exposure in the city of Stockholm Sweden, from brown and green pre-patinated copper sheet and naturally patinated copper sheet being fresh and 130 years old. Except for being geographically distant, the urban sites are characterized by large differences in climatic and environmental conditions. Measured annual runoff rates from fresh and brown prepatinated are 1, 1-1.6 g/m(2) and 5.5-5.7 g/m(2), in Stockholm and Singapore, respectively. Naturally aged copper sheet being 130 years old and green pre-patinated copper sheet show slightly higher (1.6-2.3 g/m(2)), but comparable runoff rates in Stockholm. In Singapore, runoff rates from green pre-patinated copper sheet are 8.4-8.8 g/m(2). Differences in runoff rates between Singapore and Stockholm are primarily a result of more abundant rainfall, being five to eight times larger in Singapore. Comparable runoff rates between fresh and brown-patinated copper sheet and between green naturally patinated and green pre-patinated copper sheet at each site are related to similarities in patina morphology and composition.