The authorized speed was lowered this Friday by the prefecture in Paris, where it is also not recommended to practice sports activities outside due to poor air quality. Behind this episode of pollution crossed by Île-de-France for several days, low altitude ozone, a polluting and greenhouse gas, which is formed mainly in summer, when the weather is hot and sunny. Antoine Trouche, engineer at Airparif, the association responsible for monitoring air quality in Île-de-France, answered questions from Le Point.
Viewpoint: Why are there more air pollution peaks when the weather is nice?
Antoine Trouche: “Air pollution” means everything and nothing. At the moment, we are going through a low altitude ozone pollution peak in Île-de-France. This gas has nothing to do with the ozone layer, which protects us from ultraviolet rays: it is bad and has an impact on our health.
Concretely, low-level ozone is created by a complex set of chemical reactions involving precursors: volatile organic compounds, including methane, emitted by industrial activities, solvents and certain particularly odorous plants, carbon monoxide and nitrogen oxides from road traffic.
Ozone needs the presence of these two pollutants to form, but also a particular weather: the transformation needs ultraviolet rays to operate, and is therefore facilitated by hot and sunny weather. The absence of wind and rain then increases the concentration of the gas in the air, because there is nothing to disperse the pollutants that accumulate. This is why ozone pollution peaks mainly occur in summer.
Ozone pollution is also a phenomenon linked to global warming, since it increases the temperature, which favors the appearance of the pollutant. This in turn acts as a greenhouse gas and helps to enhance global warming. It’s a vicious circle.
Is this an urban phenomenon?
It is mainly cities that are affected by ozone pollution from low altitudes, since they emit a lot of nitrogen oxide and volatile organic compounds, but ozone is a long-lasting pollutant, which has time to travel through the atmosphere before dissipating. They are therefore also found near cities, but also a little further.
In Île-de-France, ozone is thus responsible for the loss of 5 to 10% of the agricultural yields of cereal crops, wheat and potatoes, of which it disrupts the process of photosynthesis. During episodes of heavy pollution, it even necroses plants and stunts their growth. In the latest IPCC reports, ozone is taken into account in the impacts of global warming on health and agricultural yields. Ozone levels will increase, which will increase the decline in agricultural yields.
What impacts does this gas have on health?
Ozone attacks the bronchi and the pulmonary system as a whole. It thus causes inflammation of the lungs, increased frequency and severity of asthma attacks, deterioration of lung function, and increases the risk of respiratory infections. It is also responsible for the aggravation of chronic obstructive pulmonary disease, a very debilitating respiratory disease. The people most at risk are those who are already fragile in respiratory terms, children, and people who have cardiovascular problems. With the ORS Île-de-France, we have found that low-altitude ozone is responsible for around 1,700 premature deaths per year in Île-de-France.
Since when do we experience these kinds of pollution spikes? Are they more frequent?
What is special with ozone is that the frequency of pollution peaks has decreased slightly since the 2000s thanks to policies to reduce emissions of precursors, but that the quantity of gas present continuously in the air remains high and does not decrease.
However, if, during pollution episodes, the impact of ozone on human health is tangible, with a visible increase in hospitalizations, asthma attacks, and even deaths, the level of pollution persists outside of these episodes. . It’s even high enough to impact our long-term health.
What should you do to protect yourself?
The Regional Health Agency recommends limiting outdoor sports activities during pollution episodes, and being vigilant in the face of suggestive signals. If you notice shortness of breath, wheezing or abnormal palpitations, you should call your doctor. Fragile people must also contact their general practitioner to adapt their medical treatments.
Respecting the measures put in place to limit traffic also helps to reduce nitrogen oxide emissions, and therefore ozone production. But this is only an emergency response: to solve the problem of air pollution, we must put in place long-term public policies to further limit the emission of pollutants into the atmosphere.
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