In the Arve Valley, Mont Blanc overlooks a blanket of pollution

"As soon as the weather is nice, there's fog," laments the 75-year-old retiree, who has lived for 45 years in Domancy, a village in Haute-Savoie located slightly above this valley that winds between Chamonix and Annemasse.

The thick, whitish mist, nicknamed "peuf" by some Savoyards, results from the accumulation of pollutants in the air of the valley wedged between two mountain ranges, where human activities are concentrated.

"You notice it at the end of the day or in the morning when you get up," especially in dry winter weather, the retiree says. "But even in the afternoon, the valley is covered in dust."

The cause is the phenomenon known as "temperature inversion," when cold air remains trapped under warmer air, which forms a "lid" preventing pollutants from dispersing at altitude.

The main culprit: wood heating, particularly used in the many chalets in winter, followed by very heavy road transport on this major traffic route between France and Italy, and industrial activities, particularly in the bar turning sector, which is very present in Haute-Savoie.

With the arrival of cold weather, the concentration of fine particles regularly exceeds European regulatory thresholds, leading to restrictive measures for residents.

Lines of trucks

During these pollution peaks, Evelyn Zetter, 74, who has cancer, no longer goes for walks by the lake in Passy, ​​at the bottom of the valley, following the authorities' recommendations.

This Sallanches resident primarily blames the trucks on the A40 motorway, whose roar echoes continuously near the lake, where AFP met her. She describes the recurring traffic jams with "entire lines of trucks" approaching the Mont Blanc tunnel, which is used by an average of 4.500 vehicles per day, including 1.400 heavy goods vehicles.

The motorway is also essential for residents who work in Switzerland and for those who struggle to find accommodation near their workplaces due to soaring property prices in tourist towns.

Alerted, the State and local authorities implemented the Atmospheric Protection Plan (PPA) for the Arve Valley in 2010, which established the ban on open fireplaces from 2022 and the speed limit of 110 km/h on the A40 in winter.

"We are pioneers because we were in a particularly worrying situation," explains Emmanuelle Dubée, Prefect of Haute-Savoie, who welcomes a slight drop in emissions observed over fifteen years.

"Old habits"

In Cluses, posters titled "Let's fight pollution together" were posted in front of the school to encourage drivers to turn off their car engines when stationary.

According to local associations, the slight improvement in air quality is due to residents who have "reflected for themselves" and "changed their habits."

"Most people have changed their heating system," says Jean-Claude Louis, the "first" resident of Passy to install his own solar panels and who has since been offering advice to those wishing to imitate him.

While Françoise doesn't use her fireplace, she notes that many of her neighbors still heat with wood. "They won't change. These are old habits..." For her part, she uses fuel oil, which also emits pollutants.

These mixed efforts are reflected in still alarming figures: in 2024, in Passy, ​​the alert threshold for pollution by very fine particles (PM 2,5), which are particularly dangerous for health, was exceeded for 18 days.

For the first time, in February, the courts ordered the state to pay €9.000 to a family in the Arve Valley, on the grounds that their son's respiratory illnesses "were aggravated by pollution." The Lyon Court of Appeal ruled that the state committed a "fault" due to "the inadequacy of the measures adopted" to combat pollution peaks.