The science behind sandstorm pollution, explained.
Barcroft Media/Barcroft Media/Getty Images
Beijing made headlines this week, as skies turned dark orange — echoing a scene out of a post-apocalyptic movie.
Kevin Frayer/Getty Images News/Getty Images
The air quality index (AQI) reached a shocking 999 rating on Monday, indicating hazardous levels of air pollution. Good AQI typically falls between 0 and 50.