Parts Per Converter

Parts Per Converter:


Parts Per Million (ppm) Converter for Gases;

        This converter converts the measured value in [ppm] units to [mg/m3] units and vice versa. The unit ppm is used in multiple fields in various ways. As a result, the use of ppm must be indicated in the input fields below, along with how the data should be converted to the appropriate unit. Please consult the documents below for further information on the theory behind the use of ppm.

In the Molecular Weight input field, you may either select from a drop-down list or enter the value of the gas's molecular weight. If you don't know what molecular weight is, use our Molecular Weight Calculator.
By inputting the concentration in [ppm] or [mg/m3] units, the value will be converted directly and presented in the field at the bottom. The relevance is determined automatically. Use additional zeros to increase the relevance.

Parts per Million by Volume (or mole) in Air:

In the literature on air pollution, ppm refers to parts per million by volume or mole. At 1 atm, these are the same for an ideal gas and almost identical for most gases of air pollution importance. This value can also be expressed as ppmv. [1]
A volume of a specific gas mixed with a million volumes of air equals one part per million (by volume):

A microliter volume of gas in one liter of air would therefore be equal to 1 ppm:

There is a growing interest in expressing gas concentrations in metric units, i.e. g/m3. Although expressing gaseous concentrations in g/m3 units has the advantage of being metric, it is strongly impacted by variations in temperature and pressure. Furthermore, due to differences in molecular weight, comparing concentrations of different gases is challenging.

The density of the concerned gas is required to convert ppmv to a metric expression such as g/m3. Gas density can be determined using Avogadro's Law, which states that identical volumes of gases at the same temperature and pressure contain the same number of molecules. This law states that 1 mole of gas at STP enfolds a volume of 22.71108 liters (dm3), commonly known as the molar volume of ideal gas. Standard Temperature and Pressure (STP) is specified as an IUPAC standard of 100.00 kPa (1 bar) and 273.15 K (0°C).  The molecular weight can be used to compute the number of moles of the relevant gas.


Vm = standard molar volume of an ideal gas (at 1 bar and 273.15 K) [3] [22.71108 L/mol]
M = the molecular weight of gas [g/mol]

For converting ppm by mole, the same equation can be used. This can be made clear by the following notation:

By examining the dimensions of the most right section of the equation, a dimensionless value, such as the concentration in ppm, will be discovered.

The Ideal Gas Law is useful for calculating concentration in metric dimensions under various temperature and pressure conditions. The molar volume (Vn) of a gas with a temperature (T) and pressure (P) is represented by the volume (V) divided by the number of molecules (n) (P).


Vn = specific molar volume of ideal gas (at pressure P and temperature T) [L/mol]
V = volume of the gas [m3]
n = amount of molecules [mol]
R = universal gas law constant [3] [8.314510 J K-1 mol-1] or [mPa K-1 mol-1]
T = temperature [K]
P = pressure [Pa]

Because of the independence of temperature and pressure, it is evident from this equation that the percentage notation by ppm is far more practical.

Parts per Million by Weight in Water:

The concentration of gas in water in ppm is commonly expressed in terms of weight. The density of water is required to express this concentration in metric units.
Until 1969, the density of pure water had to be 1000.0000 kg/m3 at a temperature of 3.98°C and standard atmospheric pressure. This was the standard definition of the kilogram till then. The kilo is now defined as the mass of the international prototype of the kilogram [4]. Water with high purity (VSMOW) has a density of 999.9750 kg/m3 at 4°C (IPTS-68) and standard atmospheric pressure.

Temperature, pressure, and contaminants, such as dissolved gases or salinity, all influence water density. Even the concentration of gas dissolved in water has an effect on the density of the solution. Water may naturally include a specific concentration of Deuterium, which determines the density of the water. This concentration is referred to as the isotopic composition [6].
Only when the density of the water is measured can accurate conversions be calculated. In reality, the density of water is set at 1.0103 kg/m3. When you use this value to calculate the conversion, you get:


?w = density of water [1.0 ·103 kg/m3]




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