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  • Writer's pictureHinton Magazine

Summer ozone warning in Europe, as Airly reveals the summer hotspots

  • High: Several Italian cities in the top ten places with the highest concentrations of ozone

  • Low: British cities boast the lowest levels of ozone in Europe

  • Action: By addressing pollutants, especially in summer months, ozone levels can be controlled

Summer months in Europe offer an escape to enjoy the sunshine but people should tread with caution not only because of the increased UV radiation but also high levels of ozone, a harmful gas molecule. Scientists at cleantech business Airly investigated ozone levels in June 2021 across Europe to find that Italian cities have the highest concentrations.

What is ozone or O3 as it is also known? It’s a gas produced naturally on the earth’s stratosphere where ultraviolet radiation (direct sunlight) meets oxygen. It also occurs during solid electrical discharges such as thunderstorms and it smells much like the characteristic air odour after such a weather event.

Ozone becomes a real problem for people when it appears in the lower layers of the atmosphere. It either flows down from the stratosphere (upper layers), or independent chemical reactions form it. The latter happens when oxygen meets existing air pollutants, the so-called "ozone precursors", including carbon monoxide (CO), nitrogen dioxide (NO2), methane (CH4), volatile organic compounds from the combustion of gasoline or diesel, as well as hydrocarbons of natural origin (including isoprene).

Looking at the map of O3 pollution in Europe, the significant representation of Italian cities immediately catches the eye. Five of them - Asti, Lecco, Turin, Bergamo and Piacenza are characterized by an average ozone concentration higher than 120 µg / m3, adopted as the maximum safe European average (Source: It comes as no surprise that the most significant jumps in ozone concentrations were recorded during the day (9am-5pm) when sunlight was at its highest.

British cities boast the lowest O3 concentrations. In Slough, Exeter, Newport, the average ozone concentrations in June this year ranged from 30-40 µg / m3.

Ozone ranking of European metropolises

Airly ranked1 large European cities (over 100,000 inhabitants) based on their ozone concentration levels. The infamous leaders are large metropolises in the north of Italy - Bergamo, Turin and Milan. The cities which are approaching safe O3 levels are Vienna (Austria), Budapest (Hungary) and Dortmund (Germany).

Why is ozone the highest in summer?

Ozone forms when pollutants and sunlight meet. The primary sources of ozone precursors are car exhaust fumes, industrial emissions and chemical solvents. As such, high concentrations of ozone are the product of the population density and insolation. There is little wonder there are marked increases in ozone concentrations in spring and summer.

Health risks

Children and people who have asthma are particularly exposed to high ozone levels. This results in coughing, eye irritation, decreased lung capacity and increased susceptibility to infections. O3-induced inflammation also contributes to heart disease, diabetes, and other metabolic disorders.

How to reduce ozone concentration?

To fight the excess of ozone near the earth's surface, we can either passively defend ourselves (by escaping to green spaces and wearing masks with a carbon filter, which can be pretty bothersome in hot weather), or take several actions to limit the production of its precursors. While we cannot control the amount of sun, we have a significant impact on NO2 emissions in the energy and transport industry (the latter is also crucial for CO and VOC emissions). We can influence pollution from transport by not travelling in diesel cars instead choosing to take a bicycle or public transport such as a bus or tram.

How to measure ozone concentrations?

A simple way to measure ozone levels is to use stationary air quality sensors. For example, Airly air quality sensors measure the concentration of gases using the Airly PM + NO2, O3 sensor, which should be installed outside the building at the height of 1.5 m to max. 8 m and powered permanently with electricity. You can quickly check sensor readings in the mobile app or on

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