Ozone in the environment

Ozone in ambient air is a polluting gas that hods servere risks for our health. Especially patients suffering from respiratory diseases, the eldery and children experience troubles during high ozone concentrations. But also adults in good condition can be influcenced, in particular during intense physical efforts. More clarity about the causes of this ozone problem, what can be done about it and the difference with the ozone layer, can be found in the brochure "Less ozone more air" (dutch or french) published by the Belgian Federal Department of the Environment  (http://www.health.fgov.be)

Edition of ozone data

CELINE - IRCEL publishes daily since april 15, 1996, on INTERNET, a bulletin about the ozone concentrations in ambient air in Belgium.

These concentrations are measured by the Air Quality Networks of the three Belgian Regions (Flanders, Brussels and Wallonia).

In the morning of every working day , the bulletin gives the following information - corresponding to the previous day :

- the hourly maximum value for each measuring station, and the time of the day where this value has been measured.
- the 8-hourly maximum average for each measuring station , and the time of the day where this value has been measured.(this time corresponds to the end of the 8 hours period on which the average has been computed).
- the daily average ( 24 hours average between 0 and 24 h. UT) of the previous day for each measuring station.

Between 12:00 and 23:00 (local time), "real-time" data from the present-day are published every hour with :

- the actual ozone concentrations for each measuring station.
the hourly maximum value for each measuring station, and the time (local time) of the day where this value has been measured.
- the time of the last received data.

This daily bulletin allows to control whether the European Union information threshold (180 g/m3 during 1 hour) has been exceeded. Whenever this threshold has been exceeded in at least one station , CELINE-IRCEL - as it did on the previous years - sends to the concerned Ministries and Administrations , as well as to the media a bulletin in order to warn the public.

This procedure is applied systematically, even on week-ends and non-working days.

Conventions and definitions

- The concentrations are given in g/m3 (micrograms per cubic meter).

- concentration scales :

The concentration scales are based on the threshold of 180 g/m (European threshold for informing the public) and  360 g/m (alarm threshold) as 1 hour averages.


concentration (g/m)

0 30

31 50

51 70

71 90

91 111

111 145

146 180

181 250

251 360

> 360














very good


fairly good



very poor


very bad


- The day, period on which the maxima and averages are computed goes from 0 to 24 hours UT (Universal Time : similar to GMT Greenwich Meridian Time). When the summer time is applied in Belgium, it corresponds to UT time + 2 hours, in the winter it corresponds to UT time + 1 hour.

- The displayed values are only indicatives , thus they are not validated yet when they appear on Internet. They are thus not supposed to be stored in files for studies or analyses. Validated data can be obtained on request later on, following the existing procedure.

Why does this bulletin show 3 kinds of data per station ?

The hourly average :

The E.U. Directive 92/72/EEC about air pollution by ozone requests that Members States should inform the public whenever the 180 g/m3 threshold, as an hourly average is exceeded. Morover, the alarm threshold is 360 g/m3 as an hourly average. The World Health Organization (WHO) proposes, as far as the protection of the public health is concerned, a range from 150 to 200 g/m3 as an hourly average.

The 8-hourly average :

The E.U. value for the protection of the public health ( as precised in the E.U. Directive 92/72/EEC) is 110 g/m3 for the 8-hourly averages. These averages have to be computed 4 times a day : from 0 to 8 hours; from 8 to 16 hours; from 16 to 24 hours; and from 12 to 20 hours . WHO intends to revise the values of the ozone thresholds : The hourly averages should not be used anymore but would be replaced by a maximun 8-hourly average of 120 g/m3. This 8-hourly average should be computed every hour ( moving 8-hourly average).

The daily average ( 24-hourly average from 0 to 24 hours) :

The E.U. and the WHO propose a daily maximum threshold of 65 g/m3 for the protection of the vegetation.

The daily ozone data are also available on the Web site of the " Direction gnrale des ressources naturelles et de l'Environnement (DGRNE) " of the Ministre de la Rgion wallonne.