First of all, certainly when you start looking at the electricity regulation that's proposed and coming out, it looks at lower carbon dioxide using combined natural gas cycle generation. But clearly when you start looking at transportation, it's not only carbon dioxide, but nitrous oxide, sulphurous oxide, mercury, and particulate. That's certainly one of the key components in the U.S. with their Clean Air Act.
On October 6th, 2011. See this statement in context.