How is ppmv defined?

PPMV, or parts per million by volume, is defined as a measurement used to express the concentration of one substance in a gas mixture. Specifically, it indicates how many parts of a particular substance are present in one million parts of the entire volume of gas. This metric is particularly relevant in environmental science and air quality monitoring, where understanding the concentration of gases, such as pollutants or greenhouse gases, is crucial for regulatory compliance and assessing environmental impact.

Using volume as the basis for measurement is important because gases behave differently than solids or liquids; their concentration can be significantly influenced by temperature and pressure. PPMV provides a standard way to describe these concentrations in a manner that is meaningful in the context of gas behavior in the atmosphere.

Other options, such as parts per million by weight, area, or length, do not correctly represent the context in which PPMV is used, particularly when referring to gases, which makes volume the appropriate unit for this specific measurement.