Beijing warned residents that air quality had reached serious pollution levels and that people should "avoid outdoor activities" last Friday. The U.S. embassy confirmed over Twitter that pollutants had reached "hazardous" levels and and were at their worst since at least December 1. The warning follows an announcement from March of last year that the government would demand stricter monitoring of fine particulate matter by cities, and it marks the fifth warning since January 1, when the measures went into effect. The move marks a departure from China's past treatment of air quality reports. A flight grounding, road closing smog that choked Beijing in December 2011 led to outrage as stores sold out of face masks and residents independently posted air quality test results online, while the city reported that the city was "slightly" polluted. The U.S. embassy, which monitors air quality for Americans in Beijing and posts the results to a Twitter feed, reported the same smog as polluting "beyond index," a disparity that in part led to the May request that foreign embassies stop releasing independent air quality data. However, Chinese citizens have long been able to purchase inexpensive air monitoring test equipment and post the results on microblogging sites to show that the China Environmental Monitoring Center data is inaccurate. For the full story, see Earlier:,,