Idling cars produce the same exhaust that driving cars do. If you’re stopped for more than 10 seconds (other than at a stop light or bumper-to-bumper traffic), turn off the engine. That’s right, crank that key to the left or push the button and let your motor rest. The Environmental Defense Fund says that for every 10 minutes your car is off, you prevent one pound of carbon dioxide from being released into the air.
Here’s more from EDF about idling and why it’s no good.
So, at least for today, don’t let your engine run unless absolutely necessary.