I just saw a feature on Beijing air pollution on Chinese CCTV News channel.

One question was why are the measurements of the US embassy so different from the official chinese values?

The answer given was the official chinese values measure only the relatively big particles while the US embassys measurements include the very small fine dust paraticles which are the actually dangerous component of Beijing smog.

They also showed a chinese 6th grade students performing his own measures with a borrowed device for an essay he prepares for school. CCTV commented that the boy would have much less work with the essay if the authorities would publish better data.

Sometimes CCTV news is quite open with its comments.