When you live in Beijing for a while, you gain a finely tuned understanding of air. After seven years here, I feel a bit like those apocryphal Eskimos, with their thirty words for snow.

In Beijing, we talk about air purifiers the way that teen-age boys talk about cars. More than once, I’ve gone into a friend’s apartment and put an admiring hand on a top-of-the-line, IQAir HealthPro, and said, “Niiiice.” (The cost? About nine hundred bucks per room.) At our house we have a lesser brand, and the following will sound like a joke, but I’m sorry to say it’s not: the filters for these machines are so expensive that we get ours under the table, through a connection that my wife has involving a stern Russian woman from Vladivostok. How she gets them, I don’t ask and she doesn’t tell.

For Christmas last year, our families gave us air purifiers.

By now, the world has looked on with sympathy (and a soupçon of “airenfreude”) at pictures of the misery here in Beijing these days. Thanks to an extra-cold winter, which has caused people to burn more coal; an ever-increasing number of cars; and a windless few days, Beijing entered a tunnel of record-breaking air pollution this weekend—and it’s still going on. The most dangerous kind of pollution, the ultrafine airborne particles, spiked to nine hundred and ninety-three micrograms per cubic meter on Saturday. How high is that? The World Health Organization advises cities not to exceed twenty-five. (As I type this, we’re down to two eighty-five, which the U.S. Embassy describes as “hazardous.”)

For me, the clearest technical measure of the severity came from an environmental-law expert who reported that the closest the United States has ever come to measurements like this was in the midst of forest fires—and Beijing’s level this weekend was far higher than that.

I first noticed that something odd was happening around midday on Saturday, when Beijing passed the first of a series of unscientific measurements I use to take stock. First came the “indoor smog” test. When my wife and I walked into a mall in Beijing on Saturday, the air inside the vaulted-glass atrium had the color and weight of fog over a fishing village at dawn. We hadn’t noticed it before we got there because we’ve largely engineered our lives to avoid having to dwell on the issue. We live in a one-story house with windows that face the yard, in part because we discovered, years ago, that sweeping views from a high floor are just a daily reminder of all that you can’t see. We gave up running outside years ago and bought a treadmill, after a doctor-friend weighed the issue and concluded that running inside was better than going without exercise. This weekend, I climbed on the treadmill and wheezed to the end of a half an hour before deciding that we had now passed my next threshold: the “screw the treadmill” test.

By Sunday, Beijing was advising people not to leave their houses. The airport cancelled dozens of flights because pilots couldn’t see, and the capital ordered cars off the roads. Factories were shutting down, and the Web site of the environmental-monitoring center crashed. “The number of people coming into our emergency room suffering heart attacks has roughly doubled since Friday when the air pollution became really severe,” Ding Rongjing, the deputy head of cardiology at Peking University People’s Hospital, told Bloomberg News. At our house, we holed up with an air purifier and a pirated DVD of “Lincoln.” (Sorry, Daniel Day-Lewis; desperate measures.)

The smog this weekend passed another threshold I hadn’t seen before: a test we might call “the local tolerance.” For years, Chinese people called their smog “fog,” a subtle way of saying, in effect, Western countries were polluted on their way up, too, so give us a break. Not anymore. The Chinese press was full of stories about smog this weekend, including a reminder of the hideous fact that high levels of particulate matter caused a combined eight thousand five hundred and seventy-two premature deaths in Beijing, Shanghai, Guangzhou, and Xi’an last year, according to estimates in a study by Greenpeace and Peking University’s School of Public Health.

Someday, I’ll write about the political effects of environmental pollution, about how, when the middle class in places like Hungary and Taiwan eventually got fed up with their ruling parties, one of the first issues around which they organized was the environment, because it was visceral and seemingly apolitical.

But not today. Today, I’m lying low and taking shallow breaths.

Photograph by ChinaFotoPress/Getty.