In practice arithmetic operation using the specific figures may be more convenient, after finding molar volume at reference conditions. Concerning X ppm(v) of gas, of molecular weight MW and temperature T oK for ambient air: Actually ppm on volume basis is also ppm on molar basis for pressure = 1 Atm a of ambient air.ġ. Way of calculating the conversion based on ppm (v) definition is judged useful, especially when you are far from office. This calculator has been found to provide satisfactory results: The links for US EPA and European Air Quality Directive are provided below:Īn link for an online calculator for converting ppm (v) to mg/m 3 and vice-versa is provided which uses reference conditions of 25☌ and 1 atmosphere. The European 'Air Quality Directive' also uses reference conditions, however, these are not specified at their website. A prime example is the United States Environmental Protection Agency (EPA). Most agencies involved in air pollution regulation and control use reference conditions of 25☌ and 101.325 kPa(abs). This question has been raised often on the forum and even now I see a lot of process engineers failing to understand the concept and making mistakes in conversion.Īn important point is to note that a majority of the times when you are dealing with gaseous air pollutants in the atmosphere, the reference condition of temperature and pressure needs to be clearly specified.

How to calculate ppm in air