Beijing air quality is often poor, especially in winter. In mid-January 2013, Beijing's air quality was measured on top of the city's US embassy at a PM2.5 density of 755 micrograms per cubic meter, which is more than 75 times the safe level established by the WHO, and went off the US Environmental Protection Agency's air quality index. It was widely reported, originally through a Twitter account, that the category was "crazy bad". This was later changed to "beyond index".