 (PD) Photo: Dr. Edwin P. Ewing, Jr. / Centers for Disease Control and Prevention (CDC) Smog in New York, 1988 |
 (CC) Photo: Rick Kimpel Smog in Denver, 2006 |
 (CC) Photo: Carol Sawada Smog in Sao Paulo, Brazil, 2006 |
 (CC) Photo: Jim Budd Smog in London, 2007 |
 (PD) Photo: Jon Sullivan, www.pdphoto.org Smog in Los Angeles, 2003 |
 (CC) Photo: Brian Jeffrey Beggerly Smog in Beijing, 2005 |
 (CC) Photo: Andrea Squatrito Smog in Milan, italy, 2006 |
 (CC) Photo: Yulia Smirnova Smog in Moscow, 2010 |
 (CC) Photo: Lauren Brown Smog in Mexico City, 2006 |
 (CC) Photo: Thomas Galvez Smog in Kuala Lumpur, Malaysia, 2006 |
 (CC) Photo: Nina Hale Smog in Cairo, Egypt in 2008 (Pyramids in background |
 (CC) Photo: Romain Guy Smog in Tokyo, 2009 |
 (CC) Photo: Victor Villanueva Smog in New York, 2007 |
 (CC) Photo: Hernan Precht Bañados Smog in Santiago, Chile in 2006 |
 (CC) Photo: David Merrigan Smog in London in 2009 |
 (CC) Photo: Philippe Semanaz Smog in Kunming, China in 2005 |
