Burning eyes, dry cough and reduced performance: the consequences of high ozone levels

If the weather is always nice with lots of sunshine and high temperatures, it can happen that the limit values ​​for ozone are exceeded in almost all of Switzerland. This happened much more often this year than in previous years, partly due to the very sunny and warm June. On average about twice as much as last year.

While other air pollutants such as sulfur dioxide and carbon monoxide have steadily declined in Switzerland since the mid-1980s, the same cannot be said for ozone. The harmless limit value – 120 micrograms of ozone per cubic meter of air – is regularly and sometimes significantly exceeded.

Contrary to what one would expect, ozone levels in rural areas are not lower than in inner cities. The highest values ​​are often even measured on the outskirts of the city and in the adjacent rural area. “This is because the ozone precursors are carried to land by the wind,” explains Meltem Kutlar Joss, an environmental epidemiologist and project manager at the Air and Health Documentation Center of the Swiss Tropical and Public Health Institute (Swiss TPH) in Basel. “On the other hand, the fresh exhaust fumes of cars from the cities, which break down the ozone through a chemical reaction, are not transported.”

However, the wind cannot carry many precursors up the mountains. Therefore, ozone pollution in places like the Jungfraujoch is relatively low.

The difference between the north and south of the Alps is pronounced: due to the influence of the industrialized region around Milan, ozone pollution is higher south of the Alps.

According to the Basel researcher, about ten percent of the population feels the effects of the irritating gas from an ozone value of 180 µg/m³. The greater the physical exertion, the stronger the reactions. These include irritation of the mucous membranes such as burning eyes, scratchy throat, chest tightness and pain on deep inhalation. In addition, a high level of ozone pollution can increase the sensitivity of the airways to other stimuli such as particulate matter, pollen or house dust. The ability to concentrate also decreases.

These effects are usually short-lived and quickly dissipate when ozone levels fall. The long-term effects are difficult to study, but are believed to increase mortality.

The irritating gas ozone is especially endangering asthmatics and people with chronic obstructive pulmonary disease, says epidemiologist Kutlar Joss. As a review article in “Environmental International” showed, these groups of people are more likely to be hospitalized when ozone levels are exceeded. A joint review of the data from twenty countries also shows that the mortality rate increases with the short-term increase in ozone pollution. This may also have something to do with the fact that high ozone levels are associated with a higher risk of heart attack and stroke.

Yes, studies in school children, adults and competitive athletes show that. For the latter, the American environmental and health economist Jamie T. Mullins analyzed nearly 700,000 track and field athlete competition results. For example, in the men’s 5,000m race, runners ran half a minute slower on average when ozone levels were high – which is a lot given race times of around 15 minutes.

However, only the athletes were confronted with performance losses over long distances, because the ozone-limited lung function only then has a negative effect. Sprint disciplines and strength disciplines such as shot put were not affected.

First of all: Masks do not protect against high ozone pollution. Unlike particulate matter or viruses, the dust is a gas that cannot be shielded with hygiene masks.

But: “High ozone levels in the summer are no reason for healthy people to give up outdoor sports,” emphasizes epidemiologist Kutlar Joss. Because the positive effects of exercise clearly outweigh the negative effects of high ozone levels. Even small children should not be forbidden to play outside because of the high ozone pollution.

Still, she recommends exercising as much as possible in the morning and doing physically demanding work because ozone pollution is usually low enough until about 11 a.m., even when the weather is nice. This is because the ozone formed the day before rapidly decreases at night. Even a cloudy or rainy day washes the ozone out of the air. In good weather, the load is highest in the late afternoon.

Kutlar Joss also recommends that people with respiratory illnesses and allergies carry their rescue medications, as high ozone levels can trigger an attack.

It is true that maximum ozone pollution levels have fallen in recent years. “Today we no longer experience the really high peaks of values ​​above 250 µg/m³ ozone,” says Meltem Kutlar Joss. This is because the pollution with the ozone precursors has decreased, but apparently not enough. Because the number of days with limit value violations has not decreased.

According to the Federal Office for the Environment (BAFU), every individual can contribute to reducing it. This includes switching to electric motors in cars and motorcycles, using electrical appliances for hobbies and gardening instead of those with petrol engines, and the use of solvent-free or low-solvent paints, varnishes and cleaning products.

Because ozone pollution is partly the result of air pollution from neighboring countries, international efforts are needed. The EU is currently reviewing its air quality directives. “I hope that the regulations will become stricter. Because Swiss air quality would also benefit from this,” says Kutlar Joss.

The “good” ozone is formed in the stratosphere. There, at an altitude of 15 to 35 kilometers, it occurs when short-wave UV radiation hits O2 oxygen molecules. During this process, the well-known ozone layer is formed, which shields the earth from harmful solar radiation.

The unwanted ground-level ozone forms in the troposphere (0 to 15 kilometers altitude) when sunlight strikes volatile organic hydrocarbons, which occur in solvents, among other things, or nitrogen dioxide, which mainly originates from motorized road traffic. The more of these precursor substances there are in the air and the stronger the sun shines, the more ozone is formed. High temperatures also speed up the chemical reaction.

Since 1750, the average tropospheric ozone concentration has increased by more than a third, mainly due to human emissions. And as studies show, global warming will continue to increase ozone formation in many parts of the world. For example, modeling for the eastern United States suggests that climate change could increase the number of days when ozone limits are exceeded by two-thirds by 2050.

Ozone itself is the third most important anthropogenic greenhouse gas causing climate change, after CO2 and methane.