[AIVC, Air infiltration and ventilation glossary, 1992]:an expression describing the ability of a mechanical (or natural) ventilation system to remove pollution originating in a space, either of a steady state or transient nature.(see pollutant removal effectiveness)[EN 16798-3:2017, 3.4]:performance of air diffusion system in removing the pollutants from the occupied zone of a room given by relation between the pollution concentrations in the supply air, the extract air and the indoor air in the breathing zone (within the occupied zone).[ISO 16814:2008, 3.46]:measure of the relationship between the pollutant concentration in the exhaust air and the pollutant concentration in the breathing zone.