A coating that reflects shortwave radiation would significantly reduce the amount of heat generated in an urban environment.
The principal cause of the Urban Heat Island (UHI) effect is the absorption of shortwave UV radiation during the day, and the slow dissipation of the collected heat as longwave UV radiation during the night. This accounts for the larger difference in urban heat during the night when compared to other areas, than during the day. UV "blocking" materials such as Zinc Oxide absorb UV through a process known as band-gap absorption, and release the energy as heat in the form of infra red light. One may think that the conversion of UV into heat is the opposite of what should be achieved, however when the energy is more readily converted into heat it is not accumulated to the same extent, and as a result, will not be carried into the night time.
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