Concentration Converter

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

Temperature [°C] Atmospheric pressure [hPa] Molecular weight of pollutant [g/mol] 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":

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
Ammonia	NH3	17.03
Acetic acid	C2H4O2	60.05
Acetaldehyde	C2H4O	44.05
Carbonyl sulphide	COS	60.08
Formic acid	CH2O2	46.03
Formaldehyde	CH2O	30.03
Hydrogen sulphide	H2S	34.08
Hydrogen peroxide	H2O2	34.02
Ozone	O3	48.00
Nitric oxide	NO	30.01
Nitrogene dioxide	NO2	46.01
Sulphur dioxide	SO2	64.07

Background

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 )

where:

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