Difference Between ppm and ppmv

ppm vs ppmv

Both “ppm” and “ppmv” are abbreviations used in scientific calculations. They are dimensionless quantities. While using these terms one should be very specific and not be confused in using one in place of the other.

ppm
“ppm” stands for “parts per million”. It describes parts per million of any quantity by weight. This is a form which describes small concentrations. Traces of contaminants and food additives are also usually described in this manner. In various fields, such as chemistry, physics, and engineering, “ppm” is the unit to describe no- dimensional quantities as parts per notation. In science and engineering, “ppm” describes fractions of mass; in chemistry, it describes the relative presence of dissolved substances in water while in physics and engineering, expansion of a metal alloy in length with respect it its total length can be quoted as “quantity per quantity.” They all are numbers and not concerned with any kind of units of measurements.

ppmv
According to its abbreviation “ppmv” stands for “parts per million volume.” Trace gases found in the atmosphere such as sulphur dioxide, carbon dioxide, nitrogen, and other pollutants in the air are denoted by “ppmv” that is, parts per million by volume.
In cases of some liquids, “ppmv” is also used meaning a certain volume of a substance dissolved in one million parts per volume of liquid.
In cases of some liquids, if some substance is dissolved in it, it is denoted by” ppmw” or “ppm,” indicating a weight of dissolved substance in its one million weight. A unit of weight can be denoted in kg, gram, or any other weight unit. It is advisable to use ppm-by-weight or “ppmw” rather than “ppm” otherwise it may create confusion.
From the numerical point of view, it is very important as well essential to be very specific while using the terms “ppm” or “ppmv.” This confusion may result in gross errors if not denoted properly.

Calculations in percentages

“ppm” or “ppmv” can also be expressed in percentages such as:

1 ppm/ppmv means 1 part in 1,000,000 parts that is 0.0001%
5 ppm/ppmv means 5 parts in 1,000,000 parts that is .0005%
10 ppm/ppmv means 10 parts in 1,000,000 parts that is 0.001%
100 ppm/ppmv means 100 parts in 1,000,000 parts that is 0.01%
1000 ppm/ppmv means 1000 parts in 1,000,000 parts that is 0.1%
One should be careful which notation is being followed as in both, that is, American or EU notations “million” is different.
In the American notation, I billion=1,000 million
In the EU notation, 1 billion = 1,000,000 million

Summary:
1. “ppm” is a measurement of parts per million while “ppmv” is a measurement of parts per million volume.
2. “ppm” should always be followed by: “by-weight” or suffixed by “w” that is “ppmw” while “ppmv” in itself is self-explanatory and need not be suffixed or followed by any other word.

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