The Full Form of PPB is‍ Parts per billion.

ppb (or ppbm) is used to measure the concentration of a contaminant in soils and sediments. In that case 1 ppb equals 1 µg of substance per kg of solid (µg/kg).

ppb (or ppbm) is also sometimes used to describe small concentrations in water, in which case 1 ppb is equivalent to 1 µg/l because a liter of water weighs approximately a 1000 000 µg. This use of ppb tends to be phased out in favour of µg/l.

ppb (or ppb_V) is often used to describe concentrations of contaminants in air (as a volume fraction). In this case the conversion of ppb to µg/m³ depends on the molecular weight of the contaminant.

For example, 1 ppb chlorine represents one part of chlorine in one thousand million parts of air by weight, which is 1.45 µg/m³.

The ppb unit is mainly used in North America.