Which vehicles are the best and worst in your hometown?

No two cities are alike. We examined key factors leading to smog formation over the most polluted regions of the U.S. (What is smog?) By targeting the places where smog is doing the most damage, and providing vehicle information specific to the local air conditions of each region, we can help you make driving choices that protect the health of your kids and your community.

Local conditions including man-made and natural emissions of the two pollutants—volatile organic compounds (VOCs) and nitrogen oxides (NOx)—as well as temperature, wind patterns, and geography, all play a role in the formation of smog. The relative importance of the two pollutants to smog formation depends on this balance, as do the most effective ways to reduce smog. As a result, local smog dynamics determine which vehicles are best and worst in your town.