Concentration Converter

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For conversion between the two gas concentration units µg/m3 (microgram per cubic meter)
and ppb (parts-per-billion).

The calculator needs a browser that understands JavaScript

Temperature [°C]
Atmospheric pressure [hPa]
Molecular weight of pollutant
Concentration in ppb

Result :
concentration in µg/m3 :
Temperature [°C]
Atmospheric pressure [hPa]
Molecular weight of pollutant
Concentration in µg/m3

Result :
concentration in ppb:

Note that the Concentration Converter uses the temperature unit Celsius (°C). To convert from Fahrenheit or Kelvin you can use the calculator below. Type in the temperature value of your usual choice of unit, and click "Convert":

Fahrenheit:   Celsius:   Kelvin:    

Please also note that the Concentration Converter takes the atmospheric pressure into account. This parameter is rarely measured during air pollution sampling, but the pressure actually do matter as it affect the volume of a gas. However, if this factor is unknown then use the normal atmospheric pressure at sea level: 1013 hPa (which equals 1013 mbar, 760 mm Hg, or 1 atmosphere).

The Concentration Converter can be used for any compound in air. You must know the molecular weight (Mw) of the compound in question. Mw of a number of important pollutants in the museum environment include:

Compound Formula Mw
Acetic acidC2H4O260.05
Carbonyl sulphideCOS60.08
Formic acidCH2O246.03
Hydrogen sulphideH2S34.08
Hydrogen peroxideH2O234.02
Nitric oxideNO30.01
Nitrogene dioxideNO246.01
Sulphur dioxideSO264.07


The Concentration Converter is based on the equations:

C1 = ( C2 * Mw * 298 * P )/(24.45 * T * 1013 )

C2 = ( C1 * 24.45 * T * 1013 )/( Mw * 298 * P )


C1 = concentration in µg/m3
C2 = concentration in ppb
Mw = molecular weight of compound [g/mol]
P = absolute pressure of air [hPa]
T = temperature of air [K]

The equations are modified from ASTM (1991): Annual Book of Standards: Vol. 11.03, Atmospheric Analysis; Occupational Health and Safety, p. 54.

Related links:

A calculator for atmospheric moisture (by Tim Padfield): http://www.conservationphysics.org/atmcalc/atmocalc.php

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IAQ in Museums and Archives, 2001. Updated 2016.