National Clean Air Day is a nation-wide event sponsored by the Environmental Protection Agency to support President Obama's proposal to set stronger standards for ground-level ozone, a deadly pollutant that is one of the main contributors to smog. Motor vehicles contribute 25 percent of the hydrocarbon emissions in the St. Louis region which, when mixed with air, form ground level ozone. Each workday, Metro takes an average of 45,000 vehicles off the road.
According to the American Public Transportation Association, U.S. greenhouse gases from transportation represent 28 percent of total U.S. emissions. When individuals switch to public transit, they can reduce their daily carbon emissions by 20 pounds per day, or 4,800 pounds per year.