Air Quality App Stops Providing Data From U.S. Embassy As a crush of world leaders, including President Obama, descended on the often smog-laden Chinese capital Monday morning, organizers of the Asia-Pacific Economic Cooperation forum were most likely relieved by the clearish skies and relatively good air quality readings that started off the day. But having shut down thousands of factories across the region and sidelined millions of drivers to make sure the bevy of foreign presidents and prime ministers would breathe easy, the authorities were not about to allow a possible return of bad air to mar the political pageantry. Just before noon on Monday, one of China's most popular air quality monitoring apps stopped providing data from a device that sits atop the roof of the United States Embassy in Beijing. The app, China Air Quality Index, continues to provide readings from monitoring stations run by the Chinese government, but those readings tend to provide a rosier portrait of pollution levels in the capital and are viewed somewhat skeptically by many Beijing residents. According to one of the app's creators, Zhang Bin, a "relevant government department" had notified the company that it could no longer provide data from the United States Embassy in Beijing. The app, which provides air quality readings from cities across China, has been downloaded six million times. In an email exchange Monday evening, Mr. Zhang said he was "speechless" about the order and expressed concern that it might be permanent. "It's unclear, but I have little hope it will be allowed to return," he wrote. Although the timing may have been coincidental, air quality in the capital - at least according to the United States Embassy - began declining shortly after its readings were zapped from Mr. Zhang's app. From a "moderate" reading shortly before Mr. Obama descended from Air Force One, the embassy's meter edged into the zone of "unhealthy for sensitive groups" around noon and by 2 p.m. it was firmly in the red-alert "unhealthy" category. By 9 p.m. it had risen to "very unhealthy." According to the explanation accompanying the embassy's chart, an "unhealthy" level of pollution can cause "premature mortality in persons with cardiopulmonary disease and the elderly" as well as "increased respiratory effects in general population." By contrast, an average of the readings from Chinese government-run monitoring stations across Beijing found the air to be "lightly polluted." Nolan Barkhouse, a spokesman for the United States Embassy in Beijing, declined to comment on the discrepancy. "Our stuff is working just fine," he said. The Chinese Ministry of Foreign Affairs could not immediately be reached for comment Monday evening. Public dissemination of data from the embassy's rooftop monitor has long been a political sore point for Beijing. In 2009, a Chinese official asked American diplomats to stop releasing the information via Twitter, saying it could lead to "social consequences," according to a United States State Department cable obtained by WikiLeaks. In 2012, China's vice minister for environmental protection publicly complained that the embassy data was misleading because it sampled air from only one location. Embassy officials have acknowledged that the figures are not representative of air quality citywide, but say the monitor is an important resource for Americans living in the capital. Many analysts say the monitor helped prod Chinese officials two years ago to begin publicly releasing data on PM2.5, the fine particles of pollution that are 2.5 micrometers in diameter or smaller and are the most harmful to human health. Just before pulling the plug on his embassy index, Mr. Zhang, the app creator, sent out a message on the social media platform Sina Weibo telling his followers to "say goodbye" to the United States Embassy air readings. The announcement, forwarded 1,700 times, produced a torrent of cynical comments. "Hmm, this is a good way to deal with smog," wrote one user. Said another, "What developed capitalistic countries took 20 years to solve, we solved in just one minute!" Chen Jiehao contributed research.