Why Beijing Never Declares 'Red Alert' Smog Days

Beijing has a color-coded smog alert system, but its deployment is as much political as technical. According to Beijing’s environmental protection bureau, when the “Air Quality Index” (AQI)—a figure derived from real-time measurements of such pollutants as sulfur dioxide, nitrogen dioxide, PM 2.5, and PM 10 (the last two refer to the size of airborne particulate matter)—exceeds certain levels, the city should declare “yellow,” “orange,” or “red” alerts.

Pollution levels exceeding 300 AQI should trigger red alerts, which in turn would trigger a set of severe precautionary measures to protect public health—including closing primary schools and kindergartens. However, as the independent newsmagazine Caixin observed, that has never actually happened, even on Beijing’s smoggiest days.