Definitely regular, not reverse. A 2-4 foot piece of pipe over a solid 1/2" breaker bar and socket should work. Penetrating oil will help, especially if you leave it overnight(if you don't get it tonight.) Or, borrow a bigger impact gun. If you run down the pressure in your air tank, give it time to build back up. You want as high of pressure as possible for your impact. Read your manual. Tank pressure and line pressure are seperate. You want both of your guages to have the same reading. Eventually that nut will come off.