The impact of containment on air quality in the Paris region.
Provisional Assessment: Week of March 16-20, 2020
In order to limit the spread of the COVID-19 virus, containment measures were put in place by the authorities from Tuesday 17 March at noon.
This article highlights an improvement in air quality of around 20 to 30% in the Paris conurbation, following a drop in emissions of more than 60% for nitrogen oxides. Along traffic routes, this impact may be even greater. On the other hand, it was not very visible for fine particles (PM10 and PM2.5) during these first days of confinement.
Another piece of good news is that this decrease in air pollutants is accompanied by a decrease in carbon dioxide (C02), a greenhouse gas, highlighting the links between these two issues and the co-benefit to the climate of any improvement in air quality.
With the implementation of the containment measures, a significant drop in nitrogen oxide emissions was observed as soon as this action was fully implemented (a drop of more than 60% from Wednesday 18 March). Despite an increase in residential heating, this decrease is largely due to the sharp drop in road and air traffic. That of the other sectors of activity is less quantifiable because of the little information available. For nitrogen oxides, the drop in emissions is also reflected at the level of concentrations, with an improvement in the quality of the air breathed of 20 to 30% depending on the meteorological conditions encountered between 17 and 20 March. This improvement is particularly noticeable along the main roads where the levels at certain Airparif stations are close to background pollution levels: in 40 years of Airparif measurements, this situation at traffic stations has never occurred to such an extent and at so many stations.
Average maps of nitrogen dioxide pollution from 17 to 19 March 2020: in normal, containment and difference situations.
On the other hand, little impact was observed for particulate matter, which came more from sources where the decrease in traffic did not compensate for the increase due to residential heating and continued agricultural activities, combined with favourable spring weather conditions for particulate matter observed in several neighbouring regions. In fact, air quality was not as good as expected on Wednesday 18 March. However, with the strong decrease in traffic, levels did not increase to the point of placing us in a pollution episode, which would probably have been the case under normal conditions with similar conditions and normal traffic.
The change in weather conditions from Saturday 21 March, combined with the very substantial drop in emissions, particularly from air and road traffic, leads to "good" air quality in this second week of confinement. These weather conditions typical of this period of the year may nevertheless be very likely to recur.
You will find in the PDF below a summary of the impacts on the quantity of pollutants released into the atmosphere and on the quality of the air breathed by the inhabitants of the Paris region