Critical levels for air pollution

According to a new EU directive, member states shall ensure that up-to-date information on ambiet concentrations of different species is routinely made available to the public. Below is a list of the critical levels for some species where the public should be informed and alerted. The alert thresshold means a level beyond which there is a risk to human health from brief exposure and at which immediate steps shall be taken by the Member States as laid down in Directive 96/62/EC.

Ozone
Information level: 90 ppb
Alert level: 120 ppb

Nitrogen dioxide
Limit value: 1 hour mean values must not exceed 200 micrograms/m³ more than 18 times a calender year.
Alert level: 400 micrograms/m³ over three consecutive hours

Oxides of nitrogen
Limit value: Annual limit value for the protection of vegetation is 30 micrograms/m3
Alert level:

Sulphur dioxide
Limit value: 1 hour mean values must not exceed 350 micrograms/m³ more than 24 times a calender year.
Alert level: 500 micrograms/m³ over three consecutive hours

Reference
Common position (EC) No. /98. Adopted by the council on 24 September 1998 with a view to the adoption of council directive 98/ /EC relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air. File No 97/0266 (SYN). European Union, The Council.