Durability of photocatalytic self-cleaning performance of test exterior materials with thin-film coatings of commercial photocatalyst paints in snowy cold region was evaluated. The performance and the color value (brightness L^*)due to attachment of pollution was measured before and after outdoor exposure test for three years in Hokkaido and indoor accelerating test. The initial performance evaluated according to JIS R1703-2 depended on the kinds of materials and sample-preparation conditions such as coating thickness. The decrease in L^* could be interpreted by the difference in "decomposition activity index", R (JIS R1703-2). The indoor acceleration test combining irradiation by a xenon arc and freeze-thaw cycles could reproduce the results of outdoor exposure test. It has been concluded that durability of photocatalytic self-cleaning performance for three years in snowy cold region can be estimated using R after the acceleration test of samples.

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