**I have two datasets of SO**_{2}concentrations. One is in ppm while the other is in µg/m^{3}. Is there a way to convert one to the other?

Jeff Borland 04/23/00-

It's easy to convert parts per million into other concentrations if you know what sort of "parts" you have. "1 ppm SO**Vocabulary**atm

ideal gas law

ideal gas law constant

kelvin

micro

moles

parts per million

_{2}in air" could mean any of the following:- 1 gram of SO
_{2}for every million grams of air (parts per million by mass); - 1 mL of SO
_{2}for every million mL of air (parts per million by volume); - 1 gram of SO
_{2}for every million mL of air (parts per million by mass per volume).

*not*equivalent. Parts per million by volume is most convenient for gaseous concentrations, so that's what I'll assume you have.**Write "ppm" in terms of cubic meters**. There are a million cubic centimeters in a cubic meter (1 cm^{3}= (10^{-2})^{3}m^{3}= 10^{-6}m^{3}) so one part per million of SO_{2}by volume in air is actually 1 cm^{3}SO_{2}/ 1 m^{3}of air.**Convert cm**. You'll need the density of the gas at the appropriate temperature and pressure. If you don't have the density you can estimate it using the ideal gas law:^{3}of SO_{2}gas to µg SO_{2}PV = nRT

where P is the pressure, V is the volume, n is moles of gas, R is the ideal gas law constant (82.06 atm cm^{3}/mol K) and T is the temperature in kelvins. Since density is mass per unit volume and the mass of the gas is moles of gas times molecular weight M,d = g/V = M (n/V) = MP/RT

For example, at 25°C and 1.00 atm, the density of SO_{2}gas is approximately MP/RT = (64 g/mol)(1 atm)/(82.06 atm cm^{3}/mol K)(298 K) = 0.00262 g/cm^{3}= 2620 µg/cm^{3}.Multiplying parts per million SO

_{2}by volume by the density of SO_{2}in µg/cm^{3}gives you µg/m^{3}.

- 1 gram of SO

General Chemistry Online! How can ppm be converted to µg/m

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