Stephen Quake (left) and Euan Ashley review genetic risk factors that Ashley and colleagues found in Quake's genome. Norbert von der Groeben/Stanford School of Medicine hide caption

itoggle caption Norbert von der Groeben/Stanford School of Medicine

Smog covers downtown Los Angeles on Wednesday. A new report finds that the Los Angeles area had the worst levels of ozone, based on figures from 2006-2008. Nick Ut/AP hide caption

itoggle caption Nick Ut/AP