I'll also include some sites that have information on air pollution, the effects and other steps that are happening to reduce or at least control air pollution.

http://environment.nationalgeographic.com/environment/global-warming/pollution-overview/

http://greenliving.nationalgeographic.com/effects-air-pollution-agricultural-crops-2228.html

http://www.naturalnews.com/034624_indoor_air_pollution_chemicals_solutions.html

http://www.lbl.gov/Education/ELSI/pollution-main.html

http://www.lbl.gov/Education/ELSI/pollution-main.html

http://www.lbl.gov/Education/ELSI/pollution-main.html

http://www.cdc.gov/nceh/airpollution/