The map of the Lille metropolis and its main roads: during confinement (on the left), in normal times (on the right). - Atmo Hauts-de-France

  • The air observation association, Atmo, has just announced that an episode of atmospheric pollution with fine particles (PM10) had affected the Hauts-de-France region.
  • The reduction in road traffic is not enough to avoid any episode of pollution.
  • On the other hand, nitrogen dioxide pollution has been in sharp decline since the start of containment.

Much less traffic, and yet ... pollution. The air observation association Atmo has just announced that an episode of atmospheric pollution with fine particles (PM10) had affected the Hauts-de-France region, Friday and Saturday. How is this possible, in the middle of a period of confinement linked to the coronavirus epidemic?

"Road traffic is only one of the factors causing the increase in PM10 levels," explains Atmo. The reduction of this simple factor is not enough to avoid any episode of pollution. Heating, especially wood, agricultural and industrial activities, which have not stopped, also contribute. As well as the circulation of air masses from the Benelux and Central Europe last week. "

Spring in question

Especially since the arrival of spring conditions is conducive to the formation of secondary particles, according to Atmo. “These are formed by the reaction of pollutants already present in the atmosphere under special conditions, temperature and humidity, and are added to the particles directly produced by sectors other than road traffic. "

This pollution phenomenon has gradually increased until Saturday before being swept away, Sunday, by the appearance of the wind.

However, if PM10 has not disappeared from the atmosphere, this is partially the case with nitrogen dioxide (NO2), significant from road transport and automobile traffic.

Decreased nitrogen dioxide concentrations

Atmo compared the results observed since March 17, the date of the start of containment, with those usually recorded in March. "After a week of containment and the significant drop in traffic, the concentrations of nitrogen oxides and tracers in road traffic have significantly decreased," said Atmo.

These concentrations are down on average by 40% in the vicinity of traffic and by 9% in the whole region. "There is nevertheless a background level of nitrogen dioxide, linked among other things to the heating activity," said Atmo, who noted that it will take a little longer to "decide on the real impact of the drop in traffic." In general air pollution.

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  • Coronavirus
  • Containment
  • Lille
  • Pollution