Converter Parts Per Million (ppm)
Parts Per Million (ppm) Converter for Gases
This converter calculates the measured value in units of [ppm] into units of [mg/m3] and visa versa. The unit ppm is used in several branches in different ways. The use of ppm therefore has to be specified in the input fields below, in the way it should convert the value with the proper unit. For more theory about the use of ppm, please see the documentation below.
In air pollution literature ppm applied to a gas, always means parts per million by volume or by mole. These are identical for an ideal gas, and practically identical for most gases of air pollution interest at 1 atm. Another way of expressing this value is ppmv. 
A micro liter volume of gas in one liter of air would therefore be equal to 1 ppm:
Today's more and more there is an interest to express gas concentrations in metric units, i.e. µg/m3. Although expressing gaseous concentrations in µg/m3 units, has the advantage of metric expression, it has the disadvantage of being greatly influenced by changes in temperature and pressure. Additionally, because of difference in molecular weight, comparisons of concentrations of different gases are difficult. 
For converting ppm by mole, the same equation can be used. This can be made clear by the following notation:
By checking the dimensions of the most right part of the equation, there will be found a dimensionless value, like the concentration in ppm is.
To calculate the concentration in metric dimensions, with other temperature and pressure conditions the Ideal Gas Law comes in handy. The volume (V) divided by the number of molecules (n) represents the molar volume (Vn) of the gas with a temperature (T) and pressure (P).
With this equation it comes clear that the percentage notation by ppm is much more useful, because the independency of the temperature and pressure.
Parts per Million by Weight in Water
 Never, N. , Air Pollution Control Engineering. McGraw-HILL, Singapore 1995.
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