The usual equations for conversion between parts per million (ppm) and milligrams per cubic meter of air assume normal temperature and pressure. A more complex equation is required if temperature or pressure differ from normal.


(1) molecular weight of the compound

(2) atmospheric pressure in mm Hg

(3) temperature in degrees Kelvin (273.16 + C°)

(4) parts per million (ppm) or mg per cubic meter


mg per cubic meter =

= (parts per million) * (molecular weight) * (pressure) / (62.36 * (temperature K°))


parts per million =

= (mg per cubic meter) * 62.36 * (temperature K°) / ((molecular weight) * (pressure))

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