If you are concerned about air pollution, there is an excellent resource available to help match you to an agency that could use help from interested people like yourself.
Volunteer Match is an organization dedicated to pairing people up with the appropriate agencies. Visit www.volunteermatch.org to learn how you can be partnered up with a group in your area. Simply type in your zip code and choose the appropriate concern from the toolbar (you'll want the "environment" section) and you're off and running. An excellent example--those who live near Chicago should check into the Chicago Bicycle federation. This group is dedicated to many things related to bike travel, and are obviously contributing to air quality by encouraging people to use the zero-emissions bicycle as a preferred mode of travel.