MICROGRAMS PER CUBIC METER
Micrograms per cubic meter (mg/cm) is the second most commonly used expression of pollutant concentrations, after parts-per-million (PPM). The two expressions are connected by the molecular weight of the pollutant species. PPM is volume/volume. mg/cm is mass/volume. Lange's Handbook of Chemistry, page 2-78, gives 0.04131 as the number of "Moles" of gas in one liter at 22 deg. C., 760 Torr. (Typical room temperature and pressure). The weight (mass) of a mole of a gas is its molecular weight (m.w.) in grams. The relationship for conversion is:
Micrograms per cubic meter = m.w. x PPM x 41.31
See also the entry for PPM.