Cool roof technology uses materials with increased solar reflectance as a means of reducing energy usage and mitigating the urban heat island effect. These installations also impact regional air quality, as determined by research conducted by California’s South Coast Air Quality Management District and the University of Southern California.
Cool-roof installations are prescribed by California’s Title 24 building energy efficiency standards within the heavily populated and polluted South Coast Air Basin. The researchers used sophisticated meteorology and air quality computer models, measurements of cool roofing materials and detailed databases of the region’s rooftops to assess air quality impacts stemming from increased use of these materials under the standards.
Relative to traditional roofing materials, cool roof systems reflect more UV light and increase the ozone formation potential. Significant increases in fine particulate matter concentrations are also predicted and are attributed to overall cooler surface temperatures that result in weaker sea breezes and lower inversion layers.
The ozone increase can be countered by use of newer cool roofing materials that reflect the same amount or even less UV than traditional roofing materials. The increase in particulates will occur regardless of UV reflectance of roofing materials.
Although the other benefits of cool roofs could outweigh small air-quality penalties, UV reflectance standards for cool roofing materials could mitigate these negative consequences.