During long-lasting summer temperatures, the toxic gas ozone can form. But what is ozone anyway and at what thresholds does it become dangerous to health? What it has to do with ozone layer, ozone hole and high ozone levels, we explain here.
What is ozone?
Ozone is a mixture of gases consisting of three oxygen atoms (O
3
) – so it has one more oxygen atom than the oxygen in the air we breathe (O
2
). The colorless gas is an important component of the earth’s atmosphere and as such protects us – at a distance of 20 to 30 kilometers from the earth’s surface – from the dangerous ultraviolet radiation of the sun. In the case of strong solar radiation, ozone can also be formed near the ground. Excessive concentration of the gas is dangerous for humans and animals, because it can irritate the respiratory tract and eyes.
At what ozone levels does it become dangerous?
Since 1990, very high ozone levels rarely occur, and when they do, peak concentrations have decreased. However, even though high peaks have decreased significantly, the annual mean ozone level has increased in comparison. The threshold for informing the public about ozone levels is 180 µg/m (micrograms per cubic meter of air, measured as a one-hour average). Above this concentration, people who are sensitive to air pollutants should avoid, in particular, unaccustomed and vigorous outdoor exertion in the afternoon. For the rest of the population, this applies from the threshold value of 240 µg/m. Below a daily exposure (average over 8 hours) of 120 µg/m, adverse health effects are not to be expected.
Ozone and its byproducts
Ozone is counted among the so-called photo-oxidants. From this category, other substances are formed in the air near the ground during sunny weather – this is then referred to as summer smog. The photo-oxidant mixture typical of summer smog contains a large number of irritants, but not always in the same composition. The strong irritating effect of this smog on the eyes and mucous membranes of the upper respiratory tract (nasopharynx) is only partly caused by ozone, but also by other photo-oxidants that are formed as a by-product of atmospheric ozone formation. These include, for example:
- Peroxiacetyl nitrate
- Peroxibenzoyl nitrate
- Acrolein
- Formaldehyde
These substances – unlike ozone – are highly soluble in water. However, in terms of their health effects, they are less significant than ozone, because they occur in lower concentrations and are less toxic (poisonous).
Effect of ozone on the respiratory system
Ozone itself reacts almost exclusively at the point of impact, that is, on the surfaces of the respiratory tract. Because of its low water solubility, it is retained in the upper respiratory tract to a much lesser extent than, for example, sulfur dioxide. Consequently, ozone penetrates much further into the lungs. In the periphery of the lungs, the irritant gas encounters tissue that is not protected by a layer of mucus. Here, damage to the cell membrane with associated inflammatory processes can occur.
When does ozone cause harm?
About ten percent of the population is particularly sensitive to ozone. Health impairments are all the more likely:
- The higher the concentration of ozone in the inhaled air is
- The longer one is exposed to ozone
- The higher the respiratory minute volume (volume of air inhaled or exhaled during one minute) during exposure
When we exert ourselves physically, the respiratory minute volume increases. It is therefore easy to understand that ozone is especially hard on people who spend a lot of time outdoors during summer smog episodes and are physically exerting themselves. However, infants and small children are also at risk, since they have a relatively high respiratory minute volume in relation to their body size. In addition, their immune system is not yet fully developed: Additional irritation by ozone can increase susceptibility to respiratory tract infections. In addition, asthmatics, people with lung or cardiovascular diseases, and the elderly are particularly at risk.
Ozone: symptoms and health consequences
Depending on the concentration and dose, humans may experience sensory effects (odor), effects on lung function, and effects on physical performance as a result of ozone.The following symptoms occur only after several hours of exposure during simultaneous physical activity:
- Changes in lung function
- Reduction of physical endurance performance from 240 µg/m
- Inflammatory response of lung tissue from 160 µg/m at 6.6-hour exposure with intermittent physical exertion
- Increase in frequency of asthma attacks (240 to 300 µg/m).
These functional changes and impairments usually normalize over the course of one to three hours after the end of exposure. However, in the case of particularly severe exposure, small deviations can still be detected after 24 to 48 hours. Inflammation of the lung tissue can last longer. A permanent increase in the concentration of ozone in the air we breathe increases the risk of developing a respiratory disease. Other long-term consequences cannot be ruled out either. For example, ozone is suspected of causing cancer and promoting Alzheimer’s disease.
Irritation symptoms caused by high ozone levels
The following sensitivities are mentioned above 200 µg/m:
- Tear irritation (caused by accompanying substances of ozone).
- Irritation of the respiratory tract
- Cough
- Headache
- Breathing difficulties
Acute irritation symptoms of the eyes and mucous membranes are largely independent of physical activity; their extent depends mainly on the duration of stay in the ozone-polluted atmosphere.
5 simple rules against summer smog
To avoid adverse health effects caused by high ozone concentrations, the following rules should be followed:
- Since high ozone concentrations usually occur at high temperatures, a rule of thumb can be: Reasonable behavior with regard to high temperatures is also reasonable with regard to ozone.
- Before you exercise on hot days, you should be aware of the ozone weather conditions.
- Prolonged physical exertion should preferably not be placed in the midday and afternoon hours, if they are possible at other times of the day. In the morning, the ozone concentration is lowest.
- If necessary, move to a well-ventilated room. Indoors, the ozone concentration is lower.
- Take more breaks, do loosening exercises in the shade.
Daily updated ozone levels
The Federal Environment Agency (UBA) publishes ozone values and nationwide ozone prognosiss updated several times a day, including weekends. The air data comes from numerous measuring stations in Germany and reflects not only the current ozone values but also the fine dust pollution. We also provide up-to-date information on ozone values for today and tomorrow in our Biowetter.
How is ozone formed?
Ozone levels are always dependent on the weather. If the sun shines long and intensively, ozone can form. Various pollutants in our air play a role in its formation, which are released, for example, by road traffic, power plants or solvents in paints and varnishes. As a rule, ozone decomposes again after a few days, especially in areas with heavy traffic, as the substance reacts with car exhaust gases – outside cities, ozone therefore takes longer to decompose.
Use of ozone
In addition to the weather-related formation of ozone, the gas can also be formed specifically. For example, there are room air purifiers that use ozone to eliminate the smell of cigarette smoke, for example – but for health reasons, experts advise against the use of such air purifiers. Some washing machines also have a so-called ozone generator to remove bacteria and odors from laundry. In addition, ozone is used in the treatment of water, for example in waterworks or for water purification in swimming pools. The advantages and disadvantages of this method are still being researched. In alternative medicine, the disinfecting and germ-killing gas is used in so-called ozone therapy. For example, it is injected or used for external fumigation of wounds. However, the healing effect of ozone is not considered proven, so therapy with ozone is controversial.
Ozone hole – what is it all about?
As mentioned above, ozone is also found in the Earth’s atmosphere. This layer in the lower part of the stratosphere is called the ozone layer. However, there are influences that can lead to a depletion of the ozone in the ozone layer and make the ozone layer thinner – this is called the ozone hole.One of the triggers for damage to the ozone layer is considered to be CFCs (chlorofluorocarbons), a group of gases that used to be used, for example, as propellants in spray cans. The connection between the greenhouse effect and the hole in the ozone layer is also the subject of much scientific debate. Since the ozone layer protects us from the harmful effects of the sun’s rays, an ozone hole can have serious consequences for our health. However, it is not related to elevated ozone levels near the ground, which occur as part of summer smog.
