Table 4.6 - Guideline values for exposure to ozone as set by WHO, EC and under discussion in UNECE for the protection of human health and vegetation (ppb)

Sources: WHO, 1987; EC Directive 92/72/EEC; UNECE, 1988

Exposure duration Protection of human health Protection of vegetation
  WHO EC WHO EC UNECE
1 hour 76­100 88 100 100 75
8 hours 50­60 55* - - 30
24 hours - - 33 33 -
Growing season (100 days) - - 30 - -
Growing season (183 days), 9.00­16.00 average - - - - 25

Notes: * The 8-hour average is calculated as a moving average over the day, ie, it is calculated at every hour based on the 8-hourly values between minus one hour and minus nine hours before the reference time.

For ozone (O3), 1 ppb ~ 2 µg/m3