They banned the burning of funeral offerings, closed restaurants and factories, halted deliveries and took millions of cars off the roads. But Chinese leaders were unable to achieve blue skies for this week’s Asia-Pacific Economic Cooperation (Apec) meeting in Beijing, with data from the US embassy showing air pollution at six times the World Health Organisation’s safe daily limit.

The one course of action left to officials? Denying access to the US data.

As global leaders tucked into their welcoming dinner, the US reading – still available on the embassy’s own website – was “very unhealthy”, with an air quality index reading of 203. It showed the concentration of PM2.5, the smallest particulate matter, at 153 micrograms per cubic metre. The WHO says the safe daily level is 25 micrograms.

But as the Washington Post reported, Smartphone apps and Chinese websites that normally included the US figures alongside official statistics, had the former removed, while the official Chinese feed crept up to 147 or “lightly polluted”.

An app that normally carries the US data showed steadily rising levels in the morning before switching abruptly at lunchtime to an implausible “0: excellent” reading.

On the beijing-air site a notice wished the Apec summit every success and read: “On the instructions of authorities, for this month’s air quality data, please refer to figures from the Beijing Environmental Protection Bureau”.

Chinese officials argue that the US measure cannot be regarded as accurate because it is based on a reading from a single spot in Beijing.

Even the 203 measure is unremarkable by the capital’s standards. October saw unusually noxious levels of pollution, with many people blaming increased production by factories which knew they would have to shut before Apec. Runners in the Beijing marathon participated in facemasks as the US embassy PM2.5 reading reached 344 micrograms per cubic metre.

The vice-premier, Zhang Gaoli, recently said that ensuring the air was clean for Apec was the “priority of priorities”.

Among residents, “Apec blue” has become slang for something enjoyable but short-lived or unreal. Some have joked that Apec stands for “Air Pollution Eventually Controlled” while others say the air in Beijing is normally so bad that “even Bpec or Cpec blue would be better than nothing”.

Weather is a major factor affecting smog levels in the Chinese capital. But the fact that such extensive measures have failed to eradicate the problem is an indicator of just how tough a long-term battle China faces as it seeks to tackle pollution.