Beijing blocks pollution mobile app

Beijing - All the sky-clearing measures plus co-operation from the weather kept Beijing relatively free of air pollution for most of a seven-day Asia-Pacific conference. Then, toward the end as top leaders met, the smog crept back.

So, China went to Plan B: Censor the pollution monitors.

Many Beijing residents get up-to-the moment updates on pollution - including levels of dangerous PM2.5 particles - by monitoring websites and mobile phone apps.

Usually these provide two sets of readings, one from Beijing city authorities and one from the US Embassy, with the latter considered by many to be more trustworthy.

But the Embassy readings were absent from many of the sites over the past week. One website, Beijing-air.com, posted a noticing saying it had "received instructions from authorities" to only post the city numbers.