A rare March heat wave is pushing San Francisco close to 90 degrees and setting records across the West.

Researchers say smoke from wildfires accounted for up to half of all small particle air pollution in parts of the western U.S. in recent years (AP Photo/Eric Risberg, File)BILLINGS, Mont. – Wildfire smoke accounted for up to half of all health-damaging small particle air pollution in the western U.S. in recent years as warming temperatures fueled more destructive blazes, according to a study released Monday. Air pollution experts say that residents of the West Coast and Northern Rockies in particular should expect major smoke events from wildfires to become more frequent. But Mickley said there's little doubt air quality regulations helped decrease other sources of pollution even as wildfire smoke increased. The new study matches up with previous research documenting the increasing proportion of pollution that comes from wildfire smoke, said Dan Jaffe, a wildfire pollution expert at the University of Washington.