View from the Fourvière hill in Lyon this Saturday, February 6, 2021 marked by desert dust pollution which has yellowed the sky over part of France.

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KONRAD K./SIPA

  • The desert dust pollution resulted in a yellow-orange sky observed in different parts of the country on Saturday.

  • This episode, due to violent flows from the south draining a significant concentration of Saharan dust, ended in Auvergne Rhône-Alpes, very heavily affected on Saturday.

  • A not really exceptional phenomenon ...

An orange-yellow sky as impressive as it is distressing that the inhabitants of a part of France have immortalized in photos.

In the aftermath of the desert dust pollution which invaded the air of a large south-eastern quarter of the country and the south-west, the episode is almost over.

In Auvergne Rhône-Alpes, a region particularly affected by this episode, the air quality observatory recorded dust concentrations from the Sahara at a particularly high level on Saturday at various stations.

"This has resulted in the information and recommendations threshold for sensitive people being exceeded (threshold set at 50 µg / m3 on average over 24 hours) in several areas of the regional territory", specifies Atmo Rhône-Alpes, which indicates in particular that record hourly concentrations were found in multiple sectors, up to 540 µg / m3 in the Maurienne valley (Savoie).

In this department, but also in Ain, this episode of pollution notably gave rise to surreal landscapes, with ski slopes covered with a film of sand.

Rare places still concerned this Sunday

This Sunday, around 1 a.m., some stations still recorded concentrations much higher than normal (around 100 and 165 µg / m3), but by 10 a.m., the majority of the levels had come down thanks to the rain that has been slaughtered in the region in recent hours.

Still too high concentrations of dust were observed in rare places, such as in the Arve Valley, in Haute-Savoie, according to Atmo, who forecasts a complete return to normal on Monday.

As strange as it is, this phenomenon is not so exceptional, recalls the independent air quality monitoring observatory.

In December 2019, Lyon had experienced for several days the massive arrival of dust from Africa.

As early as Friday evening, a few meteorological sites had warned of the consequences of the Sirocco (a very dry, strong and hot Saharan wind) on our country.

“A powerful southerly flow will take place on Friday and Saturday, giving spring temperatures but also raising a significant concentration of Saharan dust.

Advice, wait before washing your car!

Sandy rains are likely on Saturday!

”, Thus indicated the site Lyon Météo.

Limited impact on air pollution

Most of the time, when this phenomenon occurs, it is not necessarily visible since the dust, in large quantities in the air, is carried at high altitude, between 1 and 5 km, recalls Atmo Auvergne Rhône-Alpes.

“But when these air masses reach the ground, the concentrations of airborne dust can then be significant,” adds the observatory.

But the consequences on air quality and by extension on our health would be limited.

"Due to their large diameter, these particles are less easy to penetrate into organisms than the smaller dust resulting from combustion phenomena (wood heating or automobile emissions)", estimates Atmo, recalling however that in large quantities , they can cause respiratory discomfort for fragile audiences.

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