Some regions of France have turned white in recent days: in Doubs, Seine-Maritime and Saône-et-Loire, snowflakes have covered very localized areas. But this snow cover is not entirely natural. This is “industrial” snow, a direct consequence of human pollution combined with particular winter weather conditions. Libé deciphers the specificities of this phenomenon.
What is industrial snow?
Despite the absence of disturbances, it sometimes snows in cities or near industrial complexes, reports Météo France. Indeed, in certain anticyclonic conditions, with a mass of cold and humid air, the fine particles emitted by human activities can become condensation nuclei around which water vapor will agglomerate, thus forming snowflakes. .
The formation of “natural” snow depends on the same principle. Except that it forms much higher at altitude, around grains of dust and during widespread weather disturbances, specifies the Météo-Paris site.
How are these flakes formed?
Industrial – or “urban” – snow therefore depends on very specific atmospheric conditions to form, for example a powerful winter anticyclone. This acts like a lid, trapping particles suspended in the air near the ground and prevents the dispersion of humidity and pollution, explains Météo France.
However, weather conditions alone are not enough to produce industrial snow. “In fact, it is the pollution linked to industries, traffic, heating appliances which will fill the ambient air with additional humidity but also with small solid particles called condensation nuclei”details the meteorological institute. The water vapor attaches to these nuclei, freezes and transforms into very fine snow which often falls in the form of needles. This is also one of its specificities, notes Météo France.
-Furthermore, this snow mainly falls near sources of fine particles, making polluted areas visible. The phenomenon is therefore often very localized. Under identical weather conditions but in an atmosphere not loaded with fine particles, there will be no industrial snowfall.
The phenomenon is difficult to predict, says Météo France, which argues that it is complex to properly predict the persistence of cold and humid conditions in the very low layers of the atmosphere. Moreover, “very local human emissions [industries] are not taken into account in weather models.”
How dangerous is this phenomenon?
According to the Météo Centre-Val de Loire website, “it’s better to avoid playing with it” industrial snow and keep “to swallow it”. However, this snow remains not very toxic to the human body because the quantities of fine particles are generally very low, even tiny in the flakes. In addition, as with rain, pollution located in industrial snow is washed away once it falls to the ground. “If there was no humidity, this pollution would remain trapped in the lower layers of the air, instead of falling to the ground, and we would breathe it,” adds Pascal Miquel, forecaster at Météo France, interviewed here in Orléans.
Have there been any significant episodes of industrial snow?
Although the phenomenon is not rare in France, it often goes unnoticed due to its very localized and generally unsustainable appearance. Some significant episodes have nevertheless been observed in recent years, says Météo-Paris. Like that of February 9, 2021 in Moselle, near the Cattenom nuclear power plant. “Due to bitter cold and abundant humidity accentuated by the release of water vapor from the power plant, 15 to 30 cm fell in a single night over a perimeter of approximately 10 km around the power plant alone. “, traces the site.
