Why does Chamonix have some of the worst air pollution in France?

Pollution trap: Because of its geographical feature, air pollutants tend to collect in the Chamonix valley which is one of France’s most popular ski resorts. – Filepic

It’s famous for its winter sports but few visitors know about the high levels of pollution that collect in this idyllic mountain valley.

My ears pop as the car winds its way up the mountainside. On either side, a sheer, vertical drop of over 60m looms. Ahead, just before the Mont Blanc Tunnel, is the picturesque French resort of Chamonix, where over 10,000 people live and almost five million tourists visit every year.