Ozone is a molecule (O₃) composed of three oxygen atoms (O). At very high concentrations, it is a deep-blue gas with a characteristic odor; at lower concentrations, the gas is colorless and odorless.  Ozone is a highly reactive, strong oxidizing agent that is used, for example, in water treatment. Ozone is also one of the most important trace gases in the atmosphere.

About 90 percent of the Earth’s ozone is found in the stratosphere. There, it protects against the sun’s harmful ultraviolet radiation. Ozone also occurs naturally near the ground. In addition, it is formed from oxygen and air pollutants, which primarily result from human activity. These air pollutants include, for example, nitrogen oxides from combustion processes and volatile organic compounds from solvent-based products, such as solvent-based paints. Under intense sunlight and through complex photochemical processes, this mixture leads to the formation of ozone. Ground-level ozone can form in increased amounts, particularly during summer high-pressure weather conditions. 

Primarily during the peak summer months, during prolonged periods of stable, fair weather with intense solar radiation lasting several days, ozone can accumulate in the lower layers of the atmosphere. The concentration rises continuously day by day. Over the course of a single day, the highest ozone levels occur in the afternoon between 2:00 p.m. and 5:00 p.m. In Germany, there are about 300 monitoring stations for ground-level ozone that provide information on current levels. The measurements are available, among other places, in the Federal Environment Agency’s air quality app or through the Central Air Pollution Monitoring Network (ZIMEN) of the Rhineland-Palatinate State Office for the Environment. Both sources can be found in the list of links below.

Paradoxically, the highest ozone concentrations are measured on the outskirts of cities and in adjacent rural areas, even though ozone precursors are primarily generated in city centers. However, the increased traffic volume in city centers also leads to the formation of large amounts of nitrogen oxides there. Nitrogen oxides react with ozone, leading to a reduction in its concentration. Wind currents carry the precursors out of city centers, where they can then contribute to ozone formation in outlying areas.

According to the Federal Environment Agency, elevated ozone concentrations can cause respiratory irritation, coughing, headaches, and breathing difficulties in humans, and can even lead to impaired lung function and lung diseases. The severity of these effects is primarily determined by the duration of exposure to ozone-contaminated air and the intensity of physical exertion. Discomfort, such as irritation of the eyes and mucous membranes, is primarily caused by photochemical byproducts of ozone.

A portion of the population (approximately 10 to 15 percent) is particularly sensitive to ozone, but there is no clearly definable risk group. In general, infants and young children are particularly sensitive due to their high respiratory volume relative to their body size. However, people with pre-existing conditions, such as those with asthma, are also more likely to experience health effects. In the afternoon hours, when ozone concentrations are at their highest, sports and prolonged physical exertion should be avoided whenever possible. This recommendation is also consistent with other guidelines for dealing with extreme heat. The morning hours are best for physical activity. Since increased ventilation during nice weather can allow more ozone to enter indoor spaces, it is best to ventilate in the morning hours.

A Europe-wide regulation has established threshold and target values for managing high ozone concentrations. To characterize ozone pollution, the value of 120 micrograms per cubic meter (µg/m³) of ozone serves as an 8-hour average. This limit may be exceeded on no more than 25 days per year. In addition to this long-term value, there are also warning levels that indicate direct health effects. The so-called information threshold is reached when ozone levels exceed 180 micrograms per cubic meter. At this level, there is a health risk for sensitive individuals. The alarm threshold is reached at a value of 240 micrograms per cubic meter. At this level, there is a health risk for everyone due to excessively high ozone concentrations in the outdoor air. We also provide information about this through notices posted at the Mainz Environmental Store.

In 2019, the federal government adopted a national air quality program. The program outlines measures designed to have both medium- and long-term effects. Its goal is to reduce national emissions of nitrogen oxides (NOX) and non-methane volatile organic compounds (NMVOC). The measures include, among other things, the EURO 6-TEMP standard for diesel passenger cars and the transition to renewable energy sources instead of coal-fired power plants.

Each of us can personally help ensure that ozone concentrations in our local environment do not rise unnecessarily. Those who leave their cars at home and choose to use public transportation or ride a bike instead produce fewer nitrogen oxides. Reducing electricity consumption is not only good for your wallet but also results in fewer pollutants. When purchasing paints, varnishes, and hygiene products (e.g., deodorant sprays), you should opt for solvent-free products whenever possible.