The U.S. Environmental Protection Agency has an Air Quality Index (AQI) that tops out at 500. On January 12, 2013, an air quality reading of 755 was recorded in Beijing. The AQI in New York on this same date was 19. Go here for more information about this unprecedented level of air pollution. And here for an arresting series of photos of China's toxic sky [NOTE: You can toggle between "normal" and supersmog in some of the photos]. Air quality seems to have gotten much worse than what I experienced in previous trips to Beijing (see Beijing Air). The word "apocalyptic' comes to mind.