Ammonia conc in COMBINE file

Dear all,
I would like to ask why the conversion of ppb to ug/m3 of NH3 uses the following equation in the combine file. Any clarifications are greatly appreciated!

NH3 ,ppbV ,1000.0NH3[1]
NH3_UGM3 ,ug m-3 ,1000.0


Hello Ryan,

to convert NH3 from ppm to ug/m3, you need the density of air (in kg/m3) and you also need to take into account the different molecular weights of NH3 (17.031 g/mole) and air (28.97 g/mole). The ratio of mwNH3 to mwair is 17.031/28.97 = 0.588

NH3 in ppm represents 1E-06 moles NH3 / 1 moles air
Convert ppm to ug NH3 / g air: multiply by the ratio of the molecular weights
Convert ug NH3 / g air to ug NH3 / kg air: multiply by 1000.
Convert ug NH3 / kg air to ug NH3 / m3 air: multiply by air density (in kg/m3)


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