In his study, Dr. Gauderman found that children raised in towns with PM2.5 levels of 30 had substantial reductions in lung function compared with those raised in towns with levels of 5. In the decade since his study was published, “we don’t see any evidence that functional loss is reversed,” Dr. Gauderman said. “The deficit appears to be permanent. I can’t imagine what that deficit would be with pollution levels almost 10 times higher. No one has studied that