White paint and green trees can help reduce heat and pollution in urban areas, according to a study by NASA and the U.S. EPA. An abundance of dark pavement and black roofs, which soak up sunlight rather than reflect it, can make some cities 2 to 8 degrees Fahrenheit hotter than surrounding areas and aggravate smog problems. Planting more greenery, painting roofs white, and using lighter-colored pavement can alleviate air pollution, heat, and the need for air conditioning, the study found. Baton Rouge, La., architect Coleman D. Brown replaced the coal tar roof on his business five years ago with an insulated white roof and found that his monthly air conditioning bills fell from about $2,500 to between $1,800 and $2,000. In January, the Sacramento Municipal Utility District plans to begin offering the nation’s first incentive for white roofs on homes and businesses. The Lawrence Berkeley National Laboratory has estimated that Sacramento could cut its number of smoggy days in half by doubling the space shaded by trees and adding several square miles of light surfaces.