Families in Beijing waited anxiously on Monday evening to hear whether schools would shut the next day, posing unexpected child-care challenges, after the city issued its first-ever red alert for heavy smog about 6:30 p.m. and advised school closings in an effort to protect students’ health and reduce traffic on the roads, among other measures.

Finally, around 10 p.m., teachers at one prominent Beijing elementary school contacted parents on WeChat, the Chinese messaging app: The city’s education commission had ordered schools to close for three days.

“At last. I’ve been waiting,” responded a mother with the WeChat handle “haohao.”

China’s air pollution problem is a focus of considerable anger. Despite the significance of the city’s first red alert, the smog this week is not the worst the city has seen this year. Days of heavy smog starting in late November produced levels over 500, or “beyond index.” The United States Embassy’s air-quality index in Beijing recorded 367 at 1 p.m. Tuesday, a level rated as “hazardous at 24-hour exposure,” with readings earlier on Tuesday registering about 290.