There is a difference between Canada and the U.S. The electricity regulation that is supposedly coming down that was in the Canada Gazette talked about CO2 emissions but did not talk about NOx, SOx, and mercury, whereas the EPA is actually looking at the NOx, SOx, and mercury in particulate, particularly in PM2.5. In either case, whether you're looking at propane or at natural gas, one of the things is that you'll get lower emissions in the utilization of propane and natural gas. This is a good thing in terms of environmental footprint, and it's certainly a bridge to the future.
On March 6th, 2012. See this statement in context.