If you could find a station that had enough air pressure plus cubic feet per minute and enough loose change that most gas station air pumps require now days you could probably run a small air motor driven generator. I think people would become suspicious of you hanging around the air supply for three to four hours though. I built a couple air motors after reading about air powered cars. I never could get an 1800 pound car to go over 15 mph with 4,000 pounds of air. At 150 lbs shop air the motor would spin pretty fast with no load but would bog down with the slightest load. My design needed a lot more work to improve efficiency but I am convinced that air power is only good for tools and small wenches. You would be better of offering the station attendant $10 to let you plug in for a few hours.