The California agency famous for putting the squeeze on automotive tailpipe emissions is poised to tackle dirty indoor air. In a hefty report to the Legislature completed this month, the California Air Resources Board asserts that indoor air can be as polluted and dangerous to breathe as outdoor air, costing the state at least $45 billion a year in lost worker productivity, medical expenses and premature deaths. Yet, by and large, the government does little to stem indoor air pollutants, which come from sources as disparate as cigarettes, gas stoves and certain types of air purifiers. "Efforts to reduce indoor...