Smog alert system includes NO₂, SO₂ and O₃.

Threshold values for alert

The population is informed if the concentration on an hourly basis exceeds the following values

• Concentrations of NO₂ exceeds 400 µ g/m³ or the concentration of SO₂ exceeds 500 µ g/m³. In both cases, the overrun stretch over 3 consecutive hours over a wider area (e.g. over an entire city or region (zone)).
• O₃ exceeds 180 µ g/m³

Emitted a smog alert if the concentration of O₃ on an hourly basis in 3 consecutive hours exceeds 240 µ g/m³.

In practice, only tærskelværien for information for ozone will be exceeded in Denmark. It happens very rarely (with years).

See also limit values.