INTERVIEW – By its duration and intensity, the episode of atmospheric pollution which has been raging since November 30 in France constitutes a “historical record”.
Winter 2016 will be remembered, but not for good reasons. A historic decision was taken on December 7 in Paris and the Petite Couronne. For the first time, the alternating circulation was renewed. In question: the episode of pollution with fine particles and nitrogen dioxide which has lasted for a week. The peaks are of rare intensity. So much so that the Eiffel Tower has almost disappeared from the photos of many tourists. And the Paris region is not the only one to cough. In the provinces too, the cards are red. Karine Léger, assistant to the president of the association Airparif, comes back to the explanations of this phenomenon.
What is your assessment of the past few days?
Karine Leger : We have been in a pollution episode since last Wednesday. An improvement was observed this weekend: pollution levels were sustained but without reaching the level observed Wednesday, Thursday, Friday and since Monday.
Is this peak special?
Karine Leger : We hit record levels last Thursday. The particulate matter alert level was sustained and, in addition, a nitrogen dioxide information level was crossed. These levels have rarely been reached for 10 years. You have to go back to December 2009 and December 20007 to find 2 previous sustained winter episodes. Nevertheless, last Thursday the levels were higher.
The episode has been going on for a week, is it rare?
Karine Leger : The duration of this episode is its second characteristic, especially from a health point of view. Health impacts are related to both intensity and duration. This is an exceptional episode: traditionally, they can last for several days in spring or summer. On the other hand, a winter episode that lasts so long is a historic record.
How do you explain it?
Karine Leger : Two phenomena coexist. Last week it was much colder. To the traffic source, which we find this week, has been added heating, especially wood. A weather phenomenon worsens this situation and places the pollution on the ground. The fact is that the atmosphere has been extremely stable for a week, which leads to this episode in Paris but also in other cities in France and in Europe.
Do you see the end of the episode?
Karine Leger : We already know that we will have another episode of pollution this Thursday, without knowing whether it will be an information or alert threshold. For the days to come, the weather conditions are identical. The situation is therefore likely to last for several days. But the forecasts for a pollution episode are not precise enough to give an indication over several days. We know that the high pressure persists. The situation can therefore go on.
Are the measures deployed effective?
Karine Leger : We are currently analyzing the traffic data for the day of December 6 and assessing the impact. But we tested them in 2014 and 2015. Alternating traffic reduced road traffic by 20%. The decrease in pollution levels was in the order of 5 to 10% for the day. It went up to 20% on the morning and evening peaks. It is along the main roads that the levels are highest. Gaining 20 micrograms per cubic meter of air is important for people who live nearby.
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