In Paris, on a bike, you breathe cars… This is essentially what
an Inserm study and the Sorbonne University published this Thursday. Nothing revolutionary at first glance. Still, on closer inspection, the test results yielded some surprising results.

Inserm teams followed 280 volunteers during their trip to Greater Paris. Among them, public transport users, motorists, motorized two-wheeler drivers, cyclists and pedestrians. The guinea pigs were monitored for six days using sensors located on their necks, in the “breathing zone”. The equipment made it possible to measure the concentration of soot carbon in the air breathed by the participants. In total, nearly 7,500 travel segments. “Carbon results from the incomplete combustion of fuel, in particular diesel engines,” explains Basile Chaix, research director at Inserm, in charge of the study.

Motorists more exposed, cyclists more penalized

The relevance of the study lies mainly in the price taken into account both of ambient air pollution, but also of the pollution actually inhaled by the participants. The first results make it possible to determine that it is the passengers of motorized vehicles (cars, scooters and buses) who are exposed to the greatest quantity of soot carbon linked to road traffic. This is more than the concentration of pollution measured in the air surrounding cyclists and even more than pedestrians. A given probably due to their location in the heart of traffic jams.

But looking at the soot carbon concentration inhaled by the participants, the hierarchy is completely reversed. Pedestrians and cyclists, who do not produce this pollution, are the biggest “consumers”. An inconsistency? Not at all according to Basile Chaix: “The physical effort required for walking and for cycling increases the volume of air inspired by the participants, so there is greater exposure to polluting particles. A fortiori for cyclists who have a greater proximity to road traffic. »

The paradox of physical activity

An observation confirmed by Professor Bruno Housset, pulmonologist and president of the Fondation du souffle: “We ventilate around 15,000 liters of air per day. When you exercise, this ventilation can be multiplied by 5 or 6. This therefore exposes you to more pollutants. A worrying fact, especially since the pollution is constant. The pulmonologist recalls that the effects of this type of particle can be serious: “At the respiratory level, these fine particles (PM2.5) push chronic respiratory diseases such as asthma or chronic obstructive pulmonary disease (COPD). They can contribute to the development of lung cancer, prolong infections, and they can enter the body and affect organs. »

But then how to guard against it when you are a pedestrian or cyclist? If the study is primarily intended “for decision-makers and urban planners”, as Basile Chaix points out, while waiting for bicycles to be better protected from traffic and for our urban and peri-urban modes of transport to be carbon-free, there are some ” little tricks” to limit our exposure to pollution.

Avoid traffic jams and continue the sport

The first piece of advice is to avoid pollution as much as possible. It’s not easy when you live in town. It is, however, partly possible. Also, it is preferable to favor small streets to large arteries. To change the route rather than longer traffic jams. To cross a park or a garden rather than going around it if it is on the way. “Studies adapted in 2017 in England show that from one street to another, the concentration of particles can vary significantly”, explains Bruno Housset. Healthy and sick subjects walked in Hyde Park, a large London park, and others, at the same time, strolled along Oxford Street, a busy artery a few hundred meters away. After two hours, measurements showed signs of stiffness of the vascular system in Oxford Street walkers. Not with others.

Another very popular solution could also be to give your body a boost against pollution: the mask. Very popular in Asia, long before Covid-19, its effectiveness has been little studied in the fight against pollution. However, Bruno Housset advances tests carried out in Beijing on people with and without masks. Those that didn’t showed a crunch in chicken variability, which in a healthy person varies a lot. “It’s not ultimate protection since the finest particles and gases pass. But it can make it possible to filter the largest particles, ”comments the pulmonologist.

“Whatever happens, it’s not a good idea to go running in the middle of a pollution peak. In this case, you have to limit your physical activities”, warns Bruno Housset, before ending on a more reassuring note: “When you look at the positive effects of muscular exercise compared to the effects of pollution, there is no no photo. Several studies have shown that the years of life gained through physical activity are much greater than those lost through pollution. »