Update for CF Version:17

"Area fraction" means the fraction of horizontal area. To specify which area is quantified by a variable of "area_fraction", provide a coordinate variable or scalar coordinate variable of "area_type". Alternatively, if one is defined, use a more specific standard name of "X_area_fraction" for the fraction of horizontal area occupied by X.

Mass concentration means mass per unit volume and is used in the construction "mass_concentration_of_X_in_Y", where X is a material constituent of Y. A chemical species denoted by X may be described by a single term such as "nitrogen" or a phrase such as "nox_expressed_as_nitrogen". "Drizzle" means drops of water falling through the atmosphere that have a diameter typically in the range 0.2-0.5 mm.

"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. Atmosphere water vapor content is sometimes referred to as "precipitable water", although this term does not imply the water could all be precipitated.