The Heat Island is caused by the heat transferred to the air through convection when air moves over the warm pavement.
Conventional paving materials such as asphalt and concrete have solar reflectances of 5% to 40%. This means that they absorb 95% to 60% of the energy reaching them, instead of reflecting it into the atmosphere. As a result, the effect of the Heat Island deteriorates.
Cool Pavements technologies tend to store less heat and have lower surface temperatures compared to conventional products.
They help address the problem of the urban heat island, which result in part from the increased temperatures of paved surfaces in a city or suburb. Communities make use of these pavements in the context of their efforts to reduce the heat island.
Researchers predicted that if pavement reflectance throughout a city were increased from 10 to 35 percent, the air temperature could be reduced, which would result in significant benefits in terms of lower energy use and reduced ozone levels.
For example, an earlier, separate study estimated over $ 90 million/year in savings from temperature reductions attributed to increased pavement albedo ( Solar reflectance, or albedo , is the percentage of solar energy reflected by a surface) in the Los Angeles area.
Depending on the electric power fuel mix, decreased energy demand associated with «cool» pavements will result in lower associated air pollution and greenhouse gas emissions.Cooler air temperatures slow the rate of ground-level ozone formation and reduce evaporative emissions from vehicles.
It is estimated that increasing pavement albedo in cities worldwide, from an average of 35 to 39 percent, could achieve reductions in global carbon dioxide (CO2) emissions worth about $400 billion. Additionally, for every 100 m2 of cool materials used, CO2 emissions can be reduced by 10 to 18 tonnes.