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Open Access Publications from the University of California

De-pollution efficacy of photocatalytic roofing granules

  • Author(s): Tang, X
  • Ughetta, L
  • Shannon, SK
  • Houzé de l'Aulnoit, S
  • Chen, S
  • Gould, RAT
  • Russell, ML
  • Zhang, J
  • Ban-Weiss, G
  • Everman, RLA
  • Klink, FW
  • Levinson, R
  • Destaillats, H
  • et al.

Photocatalytic building surfaces can harness sunlight to reduce urban air pollution. The NO abatement capacity of TiO -coated granules used in roofing products was evaluated for commercial product development. A laboratory test chamber and ancillary setup were built following conditions prescribed by ISO Standard 22197-1. It was validated by exposing reference P25-coated aluminum plates to a 3 L min air flow enriched in 1 ppm NO under UVA irradiation (360 nm, 11.5 W m ). We characterized prototype granule-surfaced asphalt shingles and loose granules prepared with different TiO loadings and post-treatment formulations. Tests performed at surface temperatures of 25 and 60 °C showed that NO abatement was more effective at the higher temperature. Preliminary tests explored the use of 1 ppm NO and of 1 ppm and 0.3 ppm NO/NO mixtures. Specimens were aged in a laboratory accelerated weathering apparatus, and by exposure to the outdoor environment over periods that included dry and rainy seasons. Laboratory aging led to higher NO removal and NO formation rates, and the same catalyst activation was observed after field exposure with frequent precipitation. However, exposure during the dry season reduced the performance. This inactivation was mitigated by cleaning the surface of field-exposed specimens. Doubling the TiO loading led to a 50–150% increase in NO removal and NO deposition rates. Application of different post-treatment coatings decreased NO removal rates (21–35%) and NO deposition rates (26–74%) with respect to untreated granules. The mass balance of nitrogenated species was assessed by extracting granules after UV exposure in a 1 ppm NO-enriched atmosphere. x 2 2 x 2 2 2 2 x x −1 −2

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