Chinas smoggiest city closed schools Wednesday as much of the country suffered its sixth day under an oppressive haze, sparking public anger about the slow response to the threat to childrens health.
Since Friday a choking miasma has covered a large swathe of northeastern China, leaving more than 460 million gasping for breath.
Shijiazhuang, the capital of Hebei province, was one of more than 20 cities which went on red alert Friday evening, triggering an emergency plan to reduce pollution by closing polluting factories and taking cars off the road, among other measures.
Nowhere has been hit as hard as Shijiazhuang, which has seen a huge rise in pollution.
But the city's education department waited until Tuesday evening to announce it was closing elementary schools and kindergartens, following similar moves in neighbouring Beijing and Tianjin.
The announcement said middle and high schools could close on a voluntary basis.
The statement on the education department's official social media account provoked anger.
"Are middle school students' bodies' air purifiers?" one incredulous commentater asked, adding: "Are you going to wait for us all to become sick before you step up to fix this?"
A picture from neighbouring Henan province, showing more than 400 students sitting an exam on a football pitch after their school was forced to close, was widely circulated on social media and further fuelled discontent.
Shijiazhuang has seen 10 bouts of serious air pollution so far this winter, according to the China Daily newspaper, putting it at the top of the environmental ministry's list of cities with the worst air quality.
Over the last 48 hours, levels of PM 10 -- a measure of particulates in the atmosphere -- have been literally off the charts in the city, repeatedly maxing out at 999.
Levels of the smaller PM 2.5 particles, tiny enough to be absorbed into the bloodstream and thought to be a major contributor to respiratory and cardiovascular disease, reached as high as 733, more than 29 times the World Health Organization's daily recommended maximum exposure of 25.
Shijiazhuang's smog and its government's reticence to act have tested the patience of not just the public but even state media.
On Tuesday the official Xinhua news agency published an article scolding public officials in the city for waiting to cancel schools even though smog was "off the charts".
"If (officials) turn a deaf ear or act indifferent, and the people, especially minors, are exposed to potential health risks, this is undoubtedly a dereliction of duty," it said.