Tuesday marked the fourth day this year the air quality exceeded the federal standard for ozone, compared to 12 times by the same date last year.
Kevin Green, executive director of the Clean Air Campaign says there was not a single smog alert in May.
Green says driving may also be down, perhaps because of unemployment, rising gas prices and more carpooling and telecommuting. He says more than half of smog-forming emissions of ozone come from vehicle tailpipes.
Thursday's ozone level is predicted to be "orange," meaning sensitive groups like children or people with heart or lung disease should limit outdoor exertion during the late afternoon and early evening.
http://accesswdun.com/article/2009/6/221382