It takes a lot to faze residents of a city as smoggy as Beijing. But after four straight days of air so hazardous it has defied government charts and labels, the disbelief and outrage are palpable.

Government vehicles have been pulled off the roads, production slowed at thousands of factories and children told to stay indoors. On Monday, even China’s state-run media — which usually avoid criticizing the government on such topics — ran reports and editorials acknowledging the problem and demanding solutions.

The haze that has settled over the capital highlights a thorny situation for China’s newly elevated slate of leaders, who have promised transparency and reform. Delivering those on such persistent, intractable problems as China’s environment, however, may prove difficult.

The trouble began last week with a growing fog over the city. By Friday, it had become hard to see office buildings just down the street. By Saturday, the smog had reached epic proportions, stinging residents’ eyes, causing respiratory problems and sparking a panicked run on stores selling masks and air filters.

Beijing’s municipal government reported air-quality-index levels as high as 500 Saturday night, on a scale by which U.S. experts consider anything above 150 to be unhealthy and anything from 301 to 500 to be hazardous.

But that was just half the story, because Chinese monitors stop recording at 500.

An air monitor run by the U.S. Embassy that sends out hourly tweets — and has been the subject of much official Chinese rancor in the past — showed the air quality topping out at 755, an astonishing level that the embassy called, for lack of a better description, “beyond index.”

And there it stayed, lingering between “hazardous” and “beyond index” until Monday night, when it was finally downgraded to “very unhealthy.”

Although the pollution crisis is possibly the worst in recent memory, some experts and environmental activists say it is the government’s reaction that has surprised them most.

The Communist Party’s main mouthpiece, the People’s Daily, ran a front-page editorial Monday calling the darkened sky a “suffocating siege.” China Daily said there should be a “healthy debate” about air quality and asked why there are not stricter regulations for cars, urban density and tree planting. Even the nationalistic Global Times called for more transparency and less fixation on the kind of economic growth that turns a blind eye to environmental consequences.

Some think the reversal of state media on the issue has been driven by public pressure, as well as the effect of new-media information, such as the U.S. Embassy’s air-quality tweets.

China’s officials and state media, however, have not explained their approach, limiting most of their discussion to what is causing the fog and to possible solutions.

Those answers have proved elusive. Official experts quoted in state media have blamed the crisis on factors including weather patterns, factories in neighboring provinces, increased numbers of cars, hilly terrain and more burning of coal for heat amid a cold snap.

The latest speculation in state-run media, however, could be the best news of all for Beijing’s leaders and residents. By Monday night, the Xinhua News Agency was predicting that a cold front would move through Tuesday night, probably clearing out the lingering haze.