"THERE are three kinds of lies: lies, damned lies, and statistics." The words of British statesman Benjamin Disraeli are irresistible when it comes to the topic of whether Beijing is fulfilling its pledge to improve the capital's notoriously bad air before this year's Olympics.
Last month the Herald reported that an American environmental expert, Steven Andrews, had cast doubt on Beijing's claims of a significant improvement in the number of "blue-sky" days, from just 100 in 1998 to 246 last year, due to government initiatives such as closing polluting factories and replacing buses and taxis with more energy-efficient models.
Writing in The Wall Street Journal, Mr Andrews said the only reason Beijing had achieved such results was because it moved the goalposts: measuring the air quality from less polluted parts of the city while dropping data from heavily polluted areas and lowering the standards for a blue-sky day.
Beijing has 27 monitoring stations but uses data from only some of them to calculate its air pollution index. A blue-sky day is when the index is 100 or less (on a scale of 1 to 500).
Since 2001, Mr Andrews has noted that a disproportionate number of borderline blue-sky days are being interpreted as making the standard. In 2001, about half of these borderline days - when the city's index was between 96 and 105 - ended up recorded as blue-sky days. By 2006, 98 per cent of borderline days were deemed "blue sky".
Then, a few weeks ago, Mr Andrews was astonished to find that Beijing's response to his criticism that it was manipulating the data to show improvements was to "manipulate the data even more".
From January 1, the Beijing Environment Protection Bureau has been using three new monitoring stations in less congested parts of outer Beijing. These stations, Huairou, Changping and Shunyi, have a track record of producing clean-air results.
But a monitoring station just south of Tiananmen Square in the centre of Beijing, which reported blue skies on only about 3.5 out of 10 days last year, has been removed from the network.
Not only is Beijing failing to meet its own air-quality benchmarks, those standards fail to meet international standards. In most cities the level of particulates and ozone cause the most health problems. Beijing calculates its air quality using particulates alone.
After three weeks of declining to comment, the bureau, which is responsible for delivering a target of 256 blue-sky days this year, acknowledged it had changed monitoring stations, but denied there was any intent to deceive.
It said it was normal to change stations to reflect the city's growth and while they did not measure ozone they had implemented strict controls to reduce its impact on health.