what are these ozone pollution peaks?

TO CONCENTRATE – The gas has irritating properties for the mucous membranes and, in some cases, its inhalation is dangerous, warns the Ministry of Health.

In recent days, under the effect of strong heat, many French prefectures have warned their population: part of the territory is experiencing a peak in ozone pollution (O3). The areas most affected, Tuesday July 19, were mainly the Provence-Alpes-Côte d’Azur, Auvergne-Rhône-Alpes and Île-de-France regions.

Often unknown to the general public, this gas carries several risks, both for health and for the environment.

Dispersion of gas from Wednesday

The O3 comes from a transformation between two “precursor pollutants“, often the result of human activity: nitrogen oxide, emitted in particular by road traffic, and volatile organic compounds, the main origin of which is industrial activity and plants. The chemical reaction takes place under the action of the sun’s rays. If the radiation is strong, as is the case during a heat wave, the concentration of ozone in the air increases.

From one year to the next, and especially in the summer period, “the exceedance of the (air) quality objective is more or less significant depending on the prevailing meteorological conditions“, explains Airparif, the air quality observatory in Île-de-France. It sometimes happens, during heat waves, that the O3 accumulates over time and is in quantity. “That’s not the case here», Estimates Frédérik Meleux, engineer at the National Institute for the Industrial Environment and Risks (Ineris). According to him, the current situation will not settle permanently. From Wednesday July 20, with the end of the high temperatures and thanks to a flow of air, the gas should disperse and the ozone concentrations return to more usual values.

A risk for “vulnerable” people

Such a pollution peak is not uncommon and, despite its brevity, it is not without risk. The gas has irritating properties for the mucous membranes. In some cases, its inhalation is dangerous for health. It can cause coughing, chest discomfort, painful discomfort on deep inspiration, and shortness of breath. The Ministry of Health particularly warns the most “vulnerable(suffering from cardiovascular pathologies, heart or respiratory failure, asthmatics, pregnant women and the elderly), and the ARS recommends limiting physical effort and the volume of air inhaled. In 2022, Airparif published a study reporting, for the first time, “the annual number of deaths attributable to ozone (O3) (…) assessed in Île-de-France. It is of the order of 1700 deaths“.

Peri-urban and rural areas are generally more funded than the center of large cities, such as Paris. Plants are also affected by the gas O3, which inhibits the process of photosynthesis. Studies point to a drop in crop yield and therefore a reduction in agricultural production. Moreover, as Airparif’s next generation, “ozone is also a greenhouse gas that contributes to climate change“. According to the organization,simulations assume that under future climate conditions summer ozone could pose a serious threat to human health, agriculture and natural ecosystems in Europe“.

Little room for maneuver at the national level

Faced with such prospects, reducing the concentration of precursor pollutants, whose chemical transformation is at the origin of the gas, is a necessity. “Today, a lot of work is being done to find out which pollutants act on exactly“, explains Frédérik Meleux. Research is focusing on less emitting and more efficient techniques in terms of productivity. “Some countries are already moving in this direction“, he enthuses. But not all of them, sometimes constituting an obstacle for neighboring localities. As “ozone has a rather long lifespan, lasting several days, it can be transported over great distancesand carried by masses of air, gas knows no borders.

Thus, even if actions are granted on a national scale, the concentration can remain high on the territory, “it is necessary to organize at European and international level to put in place policies to fight effectively», finish the engineer. Local measures can also be taken: in Marseille, for example, the prefecture established on Monday July 18 a differentiated circulation in the city center, in order to reduce the emission of pollutants. The return to normal traffic will occur when the air quality, in red at the start of the week, returns to more usual values.


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