Adding some ethanol alcohol to the gas tank will also help lower the emissions. Not to much no more than 15% of the total fuel in the tank. You will notice a bit less pep from the engine as alcohol has less power than gasoline when it is burned. But alcohol burns 3 times as clean as gasoline. I add it to my gasoline before my Calif emissions test every time. I have never had a car fail. One of the chemical gurus can chime in on the physics aspect.George