atmosphere_mole_content_of_semiheavy_water_vapor mol m-2 [MLM2] "Content" indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. For the content between specified levels in the atmosphere, standard names including "content_of_atmosphere_layer" are used. The construction "atmosphere_mole_content_of_X" means the vertically integrated number of moles of X above a unit area. The chemical formula for semi-heavy water is HDO, water with one hydrogen replaced by deuterium.