Liquid particles measuring 40 to 500 micrometers, are formed by condensation of vapour. By comparison, fog particles are smaller than 40 micrometers. Mists are representations of figs but differ slightly in occurrences. Fogs usually reach the level of the ground while mists only occur where water droplets are existent in the air by natural events such as humidity alterations, temperature changes, or volcanic activity. Fogs are also generally thicker and longer-lasting than mists, including occurring more frequently.