Officials in the Chinese capital declared for the first time on Monday evening that the thick smog blanketing the city was bad enough to require a red alert, the highest level of alarm.
Across the city, residents braced for the onset of another "airpocalypse" - the term that some English speakers here use for the most toxic bouts of air pollution.
An official signal of the announcement came around 6:30 p.m. Monday, when Xinhua, the state news agency, posted on its English-language Twitter account : "Beijing issues first red alert for heavy smog.
As much as anything, the red alert could be the Beijing government's response to withering criticism it received from many residents last week who wondered why it had issued only an orange alert, the second highest, during the most recent "airpocalypse."