The mists - which here cover the region of Saint-Claude in the Jura at sunrise - are a cluster of fine droplets or fine ice crystals formed in a supersaturated air on microscopic hygroscopic particles. Their composition is therefore theoretically identical to that of a cloud whose base would touch the ground. It can therefore be enriched in molecules emitted by the vegetation, very abundant in the Haut-Jura, and by vapors coming from the ground or from watercourses.