SAHARA SAND. A rain of sand is currently flying over France, giving the sky pretty orange hues, and covering the cars with a fine layer of dust. It is simply the deposit left by the sand of the Sahara. One worrying element, however: the radioactivity of this dust.
[Mis à jour le 17 mars 2022 à 11h09] This Thursday, March 17, (almost) the whole of France was able to admire an orange sky, tinted by the large quantities of Saharan sand that has been flying over France since March 14, with deposits due to the passage of precipitation. First very visible in the South-West, the phenomenon was then observed in Brittany, then in Tours, Chambord. The most affected territory remains the Pyrénées-Atlantiques, according to the Central Air Quality Monitoring Laboratory. However, it should normally fade this Thursday, March 17, and disappear completely on the 19th, after bringing radioactive particles into our air. How to explain this strange phenomenon?
The orange sky that the French can observe in mid-March is actually linked to an upwelling of sand from the Sahara. This meteorological phenomenon, while impressive, is rather common: Weather Paris indicates that it occurs several times a year, or even every season depending on the period, winter being its favorite season since the atmospheric circulation there takes on a very marked meridian component. In France and Spain, it even has nicknames: sirocco and calima respectively. It takes place when an Atlantic depression dips south and positions itself over the Iberian Peninsula, raising a strong warm wind from south to southeast over the Maghreb. If the wind is sufficiently persistent between this sector and France, it produces a “pump phenomenon”: this dust then reaches our territory directly and can lead to precipitation.
It is at this time that we observe deposits on the ground and a modification of the colors of the sky. This time, the depression is particularly important: it isolated itself towards Morocco on March 14, while, at the same time, the anticyclone firmly anchored itself over the center of Eastern Europe, overflowing on the Mediterranean. The strength of the wind, the geographical extent and the duration of the phenomenon make it an event, despite the frequency of this type of event in France. This south-to-southeast flow, dynamic enough to advect sand dust to our lands, first spread large amounts of sand dust to southwestern Spain on March 14. When was France affected by these deposits? On March 14 in the evening, rains came up over the south-west of France, before reaching the central regions such as Bordeaux or La Rochelle, covered with a rain of sand, on the night of March 14 to 15. This dust sandy areas currently extend to the north. Higher concentrations are expected to remain in the south-west, before flowing out through the German borders.
On March 15 and 16, Parisians were able to observe dry and wet deposits in the streets of the capital, a little after the French regions further south which were affected from March 14. Guillaume Séchet, from Météo Villes, explained to the newspaper Le Parisien that the massive phenomenon would reach Paris on the 16th, making its sky “very milky, a little phosphorescent, before clearing under the effect of the North-East winds”.
Significant dust concentrations in the west, particularly in the South-West, first affected on Tuesday March 15, moved towards Aquitaine on March 16. In New Aquitaine, PM10 suspended particle levels will increase this Wednesday, enough to degrade the Atmo clues air quality in the departments of the region. The prefect of Pyrénées-Atlantiques even triggered the fine particle pollution alert procedure for these two days. The sand, once passed through the center of the territory, should reach the North during the day of March 16, completely covering Paris on the 17th.
“It seems that, compelled by some marvelous lamp, a genie from the Orient kidnapped him during one of the thousand nights, and stole him from the countries of the sun to hide him in those of the fog with the loves of a beautiful prince.” Alfred de Vigny#Sand #Sahara #Storm pic.twitter.com/YVFDN4EIXU
— Chambord Castle (@domainechambord) March 15, 2022
The peak was reached in the northern half of France on Wednesday March 16… Day when all the French regions were overflown by Saharan sand and when deposits were visible on the bodies of vehicles. Since this peak could last until Saturday March 19 and the dust it propagates is harmful (because it contributes to the rise in the level of fine particles), it is recommended to wear a mask when traveling in outdoors, especially for people with respiratory problems. But is there radioactivity in this phenomenon? In fact, experts agree that the fallout from nuclear tests carried out in the 1960s left a lasting mark on the Sahara desert, as the Institute for Radiation Protection and Nuclear Safety reminds us. These fallouts come from a hundred atmospheric tests carried out by several great powers: in the final score, the USSR and the United States are neck and neck with 219 shots, then comes the United Kingdom with 23 shots, China with 22 and France with only 4 in the Sahara (but 46 in Polynesia).
The sand indeed contains cesium 137, a radioactive element which has a half-life of 30 years and which can therefore act on these particles. However, radioactivity specialists want to be reassuring since the phenomenon had already occurred in February 2021, without major consequences on air quality. Indeed, if, during this month of February, the activity concentrations of cesium 137 had been higher than the average of the activities measured in February 2019 and 2020 (measurements taken by IRSN as part of its mission to monitor the radioactivity of the air), the concentration of cesium 137 present in the fine particles of Saharan sands was “in February 2021 extremely low in the atmosphere and at ground level” recalls Jean-Christophe Gariel, deputy director general in charge of the health- environment at IRSN (comments reported by the Parisian). The health impact of these meteorological episodes is therefore considered negligible by IRSN. If health risks exist, they are no worse than those of classic air pollution: Météo-France has not communicated any operational color forecast, because this phenomenon will normally have no real impact. on personal safety.