While diligently walking my dog every morning before work, I note that a lot of people warm up their cars. I do that too, when there's ice on the windshield. (honestly, I usually forget and then end up doing a half-ass job.) Why are you warming up your car when it's over 50? I'm talking 15-30 minutes for some dipsh*ts. I'm no scientist, but that seems like a lot of excess exhaust into an already struggling atmosphere. Save yourself some money and skip the warm-up, for all of our sakes.