The emergency steps significantly reduced traffic in Beijing on Saturday, although it wasn’t clear what effect it was having on air pollution. By midday, the capital was enveloped in a smothering layer of smog, with concentrations of microscopic PM2.5 – small, inhalable particles that can penetrate deep into the lungs and are considered a reliable gauge of air quality – rising to more than 10 times the level considered safe by the World Health Organization.

The alert that will run through Wednesday is the first issued this year and comes as coal-fired heating plants are ramping up their output.