Never has Beijing had such a severe contingency plan for serious air pollution. But it is a must.

The plan, which was preliminarily adopted by the municipal government over the weekend, defines the severity of air pollution by four levels. It stipulates that if smog is expected to be severe for three consecutive days, motor vehicles will be banned according to whether their license plates have last number odd or even. In that way, the number of cars on the road will be reduced by half.

In addition, primary schools and kindergartens will close; some plants will suspend production or reduce their emission of pollutants by 30 percent; and open-air barbecues and some construction projects will also be required to stop work. Eighty percent of government cars will be prohibited from running on those days.