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### Chemical and Process Engineering Resources

 Category: The Environment Question: How do I convert gaseous pollutant concentrations from ppmv (part per million by volume) to microgram/m3? Keywords: air,pollution,conversions Answer: The conversion factor depends on the temperature at which you want the conversion (usually about 20 to 25 degrees Centigrade). The general equation is:micrograms/m3 = (ppmv)(12,190)(MW) / (273.15 + oC)where:micrograms/m3 = micrograms per cubic meter (i.e., micrograms of gaseous pollutant per cubic meter of ambient air)MW = molecular weight of the gaseous pollutantppmv = parts per million by volume (i.e., volume of gaseous pollutant per million volumes of ambient air)oC = degrees CentigradeAs an example for gaseous pollutant NOx, convert 10 ppmv to micrograms/m3 at 25 oC:micrograms/m3 = (10)(12,190)(46.01) / (273.15 + 25) = 18,811where: 46.01 = molecular weight of NO2 (i.e., NOx expressed as nitrogen dioxide)The conversion factor depends on the temperature at which you want the conversion (usually about 20 to 25 degrees Centigrade). The general equation is:micrograms/m3 = (ppbv)(12.19)(MW) / (273.15 + oC)where:micrograms/m3 = micrograms per cubic meter (i.e., micrograms of gaseous pollutant per cubic meter of ambient air)MW = molecular weight of the gaseous pollutantppbv = parts per billion by volume (i.e., volume of gaseous pollutant per billion volumes of ambient air)oC = degrees CentigradeAs an example for gaseous pollutant SO2, convert 10 ppbv to micrograms/m3 at 25 oC:micrograms/m3 = (10)(12.19)(64.06) / (273.15 + 25) = 26.19where: 64.06 = molecular weight of SO2(Keep in mind that in the USA, a billion is 109, whereas in the United Kingdom, a billion is 1012 ... and in the above equations, the USA definition is used)