I knew when I drew my bedroom curtains open this morning that I should not even have gotten up.

Drawing the curtains had no visible effect on the amount of light coming through the window. I could not see the buildings on the other side of the road because the grey fog of pollution was so thick.

A quick visit to the US embassy’s Twitter page, which posts hourly readings of Beijing’s pollution levels, confirmed what my eyes and nose had already told me. The reading was “Beyond Index,” off the charts, seven times worse than US standards for acceptable air quality.

Beijing airport shut down, so poor was the visibility.

For perspective, one way an American could breathe air like Beijing’s 20 million citizens were breathing all morning would be to stand downwind from a forest fire.

Everybody who lives here could see and feel how bad it was, but the Beijing Municipal Environmental Monitoring Center was saying on its website that the air quality was “good.”

That will soon change, the government has promised. By the end of this month Beijing will become the first Chinese city to publish hourly official data revealing the level of minute particles smaller than 2.5 microns, which is what the US embassy does.

Until now, Chinese statistics have measured only particles above 10 microns in size, giving a consistently rosier picture of the situation than the embassy's PM2.5 figures do. Official readings regularly declare “blue sky days” in Beijing when the US embassy is warning its Twitter followers that the air is “very unhealthy,” or worse.

Today was officially a “blue sky day,” according to Beijing official data for example, even though the sky was invisible this morning. There were no clouds – I could stare directly at the silver disc that was the rising sun – but the air was an acrid, pale gray soup.

The government had earlier said that municipalities would not be obliged to reveal PM2.5 figures until 2016, but a string of ghastly days over the past few weeks and an online campaign by environmental activists appear to have changed the authorities’ mind.

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Telling people the truth, of course, is only the first step toward more breathable air. Now the government has to do something about the cause of the pollution, but until then it can at least pray for windy weather.

Around noon a breeze began to blow in Beijing. I looked out of my bedroom window again; where I had been able to see less than 50 yards at dawn, now I could see the Fragrant Hills, more than 20 miles away. And the sky was azure blue.