• The end of the week will be marked by a rise in temperatures expected to reach 38 degrees in the Lyon region.

  • The air quality observatory in Auvergne-Rhône-Alpes (Atmo), describes the air in the region as "bad" and it is expected to get worse.

  • The cause is ozone, a reaction between nitrogen dioxide and oxygen on contact with the sun's rays.

38 degrees expected Saturday, 34, 35, 36 through early next week.

As for a large part of France, Lyon and the Auvergne-Rhône-Alpes region are entering a quasi-scorching episode.

The departments of Drôme and Ardèche have even been placed on heat wave orange vigilance.

The significant rise in mercury will irreparably lead to a deterioration in air quality.

Since Wednesday, the air quality observatory in Auvergne-Rhône-Alpes (Atmo) has described the air in the region as "bad" and it should get worse by the weekend.

"Predictions are difficult to make but it will be tense," says Isabelle Clostre, communication manager for Atmo.

#Lesincollables: First episode of our new video series.

We explain what #Ozone really is!

🧐 Discover the regional Ozone action plan which brings together the various levers to be activated to improve our air quality 👉 https://t.co/3kcYLy99fz pic.twitter.com/Tb0mG4rnS5

— Atmo Auvergne-Rhône-Alpes (@atmo_aura) May 25, 2022


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Formation of an ozone layer

"The skyrocketing temperatures contribute to the formation of a polluting gas: ozone", explains Isabelle Clostre, specifying that it is only very rarely emitted directly by human activity.

“It forms because of the reaction between the sun's rays and already existing pollutants, called precursor pollutants like nitrogen dioxide,” she continues.

To prevent the appearance of ozone, it is therefore necessary to attack the precursor pollutants by “very strongly reducing the emissions of volatile organic compounds, certain industrial activities, methane emissions and transport”, states Isabelle Clostre.

But measures are “too rarely taken”, she believes.

Or late.

If the alert threshold for qualifying the air as "bad" has been set by the observatory at 130 micrograms of ozone per m3 of air, the prefecture uses another scale which raises the alert threshold to 180 micrograms .

“There is a significant delta”, regrets Isabelle Clostre.

“The same precursor pollutant creates ozone and also destroys it”

Another factor comes into play to eliminate nitrogen, a more surprising factor and above all much more difficult for humans to manage.

To do this, you have to do a little chemistry: ozone is formed by nitrogen dioxide (emitted by combustion engines) and oxygen when they come into contact with the sun's rays, as explained above.

But naturally, and without contact with the sun's rays, nitric oxide, also emitted by combustion engines, destroys ozone particles.

"The same precursor pollutant creates ozone and also destroys it", simplifies Isabelle Clostre.

This phenomenon of destruction creates a paradox.

“As there are more cars in big cities, there is more nitric oxide.

And once the sun has set, it will attack the ozone.

In rural areas, this phenomenon will therefore be much less”, specifies the communication manager of Atmo.

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