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Which health effects are caused by high ozone values?

Because of its strong oxidising capacity, ozone can cause some health effects, depending on the concentration in the air, the exposure time, the sensitivity of the exposed persons and their level of activity. The table below shows an overview of the principal health effects resulting from brief exposure:

Exposure levelHealth effects
mild response

max 1 hour ozone concentration: 180-240 µg/m³

average decrease of lung functiona <5%, for sensitive persons <10%

incidental eye irritation (independent from physical effort)

incidental pulmonary symptoms such as coughing for sensitives

moderate response

max 1 hour ozone concentration: 240-360 µg/m³

average decrease of lung functiona 5-15%, for sensitive persons 10-30%

irritation of eyes, nose and throat (independent from physical effort)

pulmonary symptoms such as coughing, pain in the chest, dyspnoea for sensitives

increasing severity and frequency of symptoms for persons with COPDb

severe response

max 1 hour ozone concentrations: >360 µg/m³

average decrease of lung functiona >15%, for sensitive persons >30%

pulmonary symptoms such as persistent coughing, pain in the chest, dyspnoea

possible feelings of discomfort, shortness of breath, headache, nausea, dizziness for sensitives

strong increase of severity and frequency of symptoms for persons with COPDb

a Possibly paired with inflamation reactions, increase hyperactivity of pulmonary tract and change in lung clearing
b Chronic obstructive pulmonary disease

Ozone can evoke different health effects, among which changes in lung function; The other compounds present in the 'summer smog cocktail' cause stinging eyes, coughing and irritation of the mucous membranes. The appearance of these symptoms is dependent on different factors:

the ozone concentration: the higher the concentration, the more people will show symptoms and the more severe the complaints will be. It is however impossible to accurately tell which symptoms can be expected from which concentrations onwards.

the individual sensitivity: persons with pulmonary tract afflictions will notice an effect sooner than persons with a normal lung function. Children can also be expected to be more susceptible. In addition, there is a so-called group of 'responders' (about 10% of the population) who are more sensitive for smog episodes for reasons unknown.

the effort made: by making intensive effort outdoors, breathing will speed up and more air will pass through the lungs each second. In comparison with a resting person , this results in a greater exposure to ozone and thus a higher probability of effect.

The European treshold of 180 µg/m³ for informing the population may thus not be viewed as an effect treshold value under which absolutely no one will suffer any effect at all. However, the WHO (in 1990) postulated that the effects of concentrations lower than 200 µg/m³ will be limited in severity and  will only prevail in less than 5% of the total population. Warning the whole population at lower concentration levels is thus not advised.

As such, it concerns a gliding scale and, while somewhat artificially, it is possible to talk about a mild response at (hourly mean) concentrations of 180-240 µg/m³, a moderate response at 240-360 µg/m³ and a severe response above 360 µg/m³.

It is possible to reduce the effects by taking some precautions. From the above, it is clear that the effect of ozone peak episodes can be avoided or limited by avoiding heavy physical outdoor activity at noon or during the early evening (12 am - 8pm). These precautions are to be taken by individual persons with sensitivity of the pulmonary tract and children, starting from concentrations of 180 µg/m³; From 240 µg/m³ onwards, the whole population should follow these guidelines. In case of occurring physical complaints, it is of course useful and advised to consult the family doctor, who is best acquainted with the personal health condition of the patient and thus best positioned to grant further personal advice.