Pollution

In 1952, London was covered in a thick blanket of sulfur oxides for two weeks. Ever since this "smog" incident that caused 4,500 deaths, any mention of "air pollution" causes politicians and media to focus on pollution peaks.

However, these are not the most deadly. A recent study carried out in the city of Caen shows that for 100 deaths related to air pollution, only 5 are caused by peaks. What then causes the other 95? What is the insidious and discrete pollution that lurks behind these pollution peaks?

Answering these questions means first asking more trivial ones. This is what the film undertakes. What is a pollutant, given that over 200 substances contribute to air pollution in our cities? How do we monitor it, when a gas like ozone can migrate over 500 km from its emission point?