A natural question is whether lighter surfaces are a significant disadvantage in winter. In fact, they make relatively little difference in the temperature because daily solar radiation is much reduced. Thus on a clear December day in New York, solar gain is only 25 percent of its June daily value, and cloudier average weather reduces this by one-fourth to one-eighth. There is indeed the inconvenience that on a clear winter day in New York, thin patches of ice melt more slowly on a lighter-colored roadway, but this is more than offset by the summer reduction of smog. Dark surfaces contribute about two-thirds of summer heat islands, which in turn cook smog faster. In Los Angeles, the heat island is responsible for about one-third of the smog episodes.