China to US embassy: Stop telling people how bad the air is in Beijing.

The Chinese government today warned the US Embassy in Beijing to stop telling the world just how bad the capital’s air really is.

For the past three years or so, the embassy has Tweeted the hourly readings from a pollution monitor on its roof, providing the only real time indicator of what we are breathing here.

Deputy Environment Minister Wu Xiaoqing, however, told reporters today that this was a violation of the Vienna Convention on Diplomatic Relations. Only the Chinese government is allowed to measure and publish air quality information, he said.

The trouble with that is that I am not the only person in Beijing who has sometimes found it hard to reconcile the soupy grey fog that I often see outside my window with the Beijing Municipal Environmental Monitoring Center’s insistence that pollution is “light.”

The US embassy spokesman was unavailable to comment on Mr. Wu’s admonition, but @BeijingAir, its Twitter feed, was still posting at 6 p.m.; it found the air to be “Unhealthy for Sensitive Groups.”

That is a definition taken from the US EPA, and Wu said it was not fair to judge Chinese air by American standards, which are stricter than Chinese ones, because of “our current stage of development.”

This is not the first time the US Twitter feed has got into trouble. On Nov. 19, 2010, when the Air Quality Index soared above 500 – the top of the US scale – the reading was described in a tweet as “crazy bad.”

The term appeared to have been inserted into the monitoring program by a programmer who never expected such an outlandishly high reading: Anything over 300 “would trigger a health warning of emergency conditions” in America, according to an EPA website.

Nowadays, readings over 500 (20 times higher than World Health Organization guidelines) are described simply as “beyond index.”

The Beijing municipality website publishes its own hourly readings of PM 2.5 tiny particulate matter, regarded as especially dangerous, but only 24 hours after the fact. It also publishes an average figure for air quality over the previous 24 hours, but does not characterize it as good, bad, or hazardous.

Wu’s warning to the US embassy will doubtless re-focus public attention on the real quality of Beijing’s air, which cannot be good for the authorities. What’s odd is that for the past few early summer days here the air has mostly been clear, and even gloriously sharp on one or two evenings.

If the embassy Twitter feed dies, we shall just have to go back to trusting our eyes and our noses. Just because we cannot put a scientific figure to it, doesn’t mean we don’t know what we are breathing.