text: The conversion equations depend on the temperature at which the conversion is wanted (usually about 20 to 25 °C).  At an ambient sea level atmospheric pressure of 1 atm (101.325 kPa or 1.01325 bar), the general equation is:
  and for the reverse conversion:
  Notes:
  * 1 atm = absolute pressure of 101.325 kPa or 1.01325 bar
  * mol = gram mole and kmol = 1000 gram moles
  * Pollution regulations in the United States typically reference their pollutant limits to an ambient temperature of 20 to 25 °C as noted above. In most other nations, the reference ambient temperature for pollutant limits may be 0 °C or other values.
  * Although ppmv and mg/m have been used for the examples in all of the following sections, concentrations such as ppbv (i.e., parts per billion by volume), volume percent, mole percent and many others may also be used for gaseous pollutants.
  *Particulate matter (PM) in the atmospheric air or in any other gas cannot be expressed in terms of  ppmv, ppbv, volume percent or mole percent. PM is most usually (but not always) expressed as mg/m of air or other gas at a specified temperature and pressure.
  * For gases, volume percent = mole percent
  * 1 volume percent = 10,000 ppmv (i.e., parts per million by volume) with a million being defined as 10.
  * Care must be taken with the concentrations expressed as ppbv to differentiate between the British billion which is 10 and the USA billion which is 10 (also referred to as the long scale and short scale billion, respectively).