Certain "cool roof" materials could slightly increase regional air pollution: U.S. study

2017-08-07 21:55:33 GMT2017-08-08 05:55:33(Beijing Time) Xinhua English

WASHINGTON, Aug. 7 (Xinhua) -- Widespread installation ofcertain "cool roof" materials, typically light-colored and highlyreflective, could slightly increase regional ozone and fineparticulate pollution levels, a U.S. study said Monday.

"Numerous scientific studies have established that replacingdarker roofs and building materials with highly reflectivematerials can reduce peak daytime temperatures and mitigate theso-called 'urban heat island effect' where cities can be severaldegrees warmer than less-urbanized surrounding areas," according tothe study published in the U.S. journal Proceedings of the NationalAcademy of Sciences.

"However, many cool-roofing materials reflect more ultravioletlight (UV) than their traditional counterparts, increasing thepotential for ozone formation," said the study. "UV rays fuel smogformation on their way down to Earth. When cool roofs bounce UVrays back up into the atmosphere they create a "double-shot" ofozone formation."

The findings, conducted by scientists at the South Coast AirQuality Management District (SCAQMD) and the University of SouthernCalifornia (USC), were based on meteorology and air qualitycomputer models, measurements of cool roofing materials anddetailed databases of rooftops of the South Coast Air Basin, aregion of southern California encompassing Orange County and theurban portions of Los Angeles, San Bernardino, and Riversidecounties.

"Cool roofs have many benefits including reduced energy use forcooling and mitigation of the significant health impacts of heatwaves," Wayne Nastri, SCAQMD's executive officer, said in astatement.

"While the future, widespread use of certain kinds of coolroofing materials could slightly increase air pollution levels, wein no way want to discourage this technology. This study shows whatneeds to be done to help cool our cities and avoid increasing ozonelevels as an unintended consequence."

The researchers said cool roofing materials are available todaythat reflect the same amount or even less UV than traditional,roofing materials.

As a result, the predicted ozone increase can be avoided if acomprehensive roofing standard is adopted to prevent the overall UVreflectance of newly-installed cool roofs from increasing.

However, the predicted small increase in PM2.5 levels is due tooverall cooler surface temperatures resulting in weaker sea breezesand lower inversion layers, and will occur regardless of UVreflectance of roofing materials, according to the study.

"This study highlights the importance of considering howstrategies used to mitigate one environmental issue can haveco-benefits and/or unintended consequences on other environmentalsystems," said study author George Ban-Weiss, a professor of civiland environmental engineering at USC. "Whether air pollutionimproves or worsens from cool roof installations depends on a hostof competing chemical and meteorological factors."

"Given that our study focuses on the Los Angeles basin, futureresearch is needed to investigate how these competing processesdictate air pollution impacts in cities around California andbeyond," Ban-Weiss said. Enditem