The suspension of part of the automobile traffic and economic activities may suggest this. But does this be true?
THE QUESTION – Does the containment of the population favor an improvement of air quality in the capital and around the Paris region?
Insofar as there is a drop in vehicle traffic, the closure of many factories, and a reduction in polluting activities, one might intuitively think that air pollution is decreasing. The reality is more complicated.
The indicator of Airparif, the association that measures the air quality, indicates an average air quality from April 8 to 10. The persistent good weather in the capital and the absence of strong winds favor the increase of a polluting gas, very irritating for the bronchi, the tropospheric ozone (which is just above the city). “Air quality is less degraded than without containment,” said an Airparif spokesperson.
Atmo-France
However, next week Atmo-France, which brings together all the regional air quality associations, will give the state of pollution throughout the territory, compared to that which would have been without containment. It should announce that there is an overall improvement, especially for nitrous oxides, such as NO2. This last molecule is mainly produced by road traffic. However, according to recent modeling by Ineris, corroborated by satellite measurements, containment caused a sharp drop in road traffic, in France and Europe, which led to a 50% reduction in NO2 emissions.
Two fine particle pollution peaks
As the trips estimated around 15.5 million per day in Ile-de-France have decreased in enormous proportions, the concentrations measured for nitrous oxides by Airparif have fallen by more than 50%.
But in the case of fine particles, the situation is more complicated. Since the start of containment, two peaks of pollution with fine particles, in particular PM2.5, have been observed, on 20-21 and then on 27 and 28 March. Heating with wood, which directly produces fine particles in the air, increased slightly until early April, as households were confined to their homes, and the temperatures were relatively cool.
Also, spring is a special period due to the spreading of nitrogenous fertilizers by farmers. This activity increases the concentration of ammonia in the air and, due to complex chemistry in the atmosphere with nitrous oxides, is a ” precursor of fine particles, in particular PM2.5 (which make 2.5 microns in diameter),” explains Camille Viatte, a researcher at Latmos (Laboratory of atmospheres, environments, spatial observations) of the CNRS, Sorbonne University, and Paris-Saclay University. And these PM2.5 remain suspended in the air for a long time.
Meteorology
“Meteorology plays an important role. Since there has not been abundant precipitation since March 5, many fine particles remain in the air. For their concentrations to drop significantly, heavy rains or strong winds will be needed,” adds Camille Viatte. She knows what she is talking about. The scientist has had since December 2019 the only instrument that directly and automatically measures, day and night, the concentrations of ammonia in the air of the capital, installed above a building on the Jussieu campus, in Paris.
This means that without containment, the peaks of pollution with fine particles would have been even higher in the sky of Ile-de-France. This situation is all the more worrying since researchers at Harvard have just established a direct link between the fatality rate at COVID-19 and chronic exposure to PM2.5.
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