Cool roofs are required on most new non-residential buildings in California, but the regulation may be worsening smog.
Cool roofs combat the urban heat island effect by reflecting heat back into the atmosphere. But they also reflect more ultra-violet (UV) light back into the atmosphere, creating more favorable conditions for the chemical reaction that forms ozone or smog.
Southern California would violate federal particulate matter standards for an additional two days a year if cool roofs are widely adopted throughout the region, according to a study by the state’s South Coast Air Quality Management District. Smog would also worsen, especially in Riverside and San Bernardino Counties.
Nevertheless, a researcher for the air quality district said the benefits of cool roofs including lower energy bills, reduced energy consumption, and fewer people suffering from heat-related illnesses would likely outweigh the drawbacks.