Police were checking cars throughout Paris on Monday, including near the Arc de Triomphe, as the city tried to cut air pollution by instituting odd-even driving restrictions.
Philippe Wojazer /Reuters /Landov
Skyscrapers are obscured by heavy haze in Beijing on Jan. 13. Air pollution remains a serious — sometimes overwhelming — problem, but researchers say environmental technology is available to solve it.
Ng Han Guan/AP