Number of PM2.5 Monitors in China

China has gone from having monitors for small airborne particulate matter in only 47 cities in 2002 to monitors in 367 cities in 2015. This year, China also revised its air crisis policy, originally announced in 2013. It requires officials to raise the red alert whenever the air quality index is forecast to rise above 200 for 72 straight hours. The red alert allows for the suspension of industrial production and vehicle use. Read more NY Times