How to convert PPM values of nitrogen oxides and sulfur dioxide into milligrams per cubic meter

This post was last edited by ylb913 on 2016-12-24 at 13:43. In fact, the original unit for analyzing nitrogen oxides and sulfur dioxide in flue gas should be mg/m3; ppm is a value that was derived through conversion later on. Nitrogen oxides are typically expressed as NO, with a molecular weight of 30. The molecular weight of SO2 is 64; the unit for molecular weight is “grams per 22.4 liters”, or milligrams per 22.4 milliliters, or kilograms per 22.4 cubic meters. 1. Assuming that the unit is volume ppm, that is, 1 ppm = 1 milliliter per cubic meter, then for nitrogen oxides: 1 ppm = (1/22.4) * 30 = 30/22.4 = 1.34 mg/m3. For sulfur dioxide, 1 ppm = 64/22.4 = 2.86 mg/m3. 2. The assumption is that the value is given in terms of mass ppm (weight ppm is generally not used for gases); this corresponds to the relationship of “1 ppm = mg/kg”. To carry out the conversion, it is necessary to know the composition of the flue gas, so as to determine its average molecular weight. If the average molecular weight of the flue gas is 32, then its density is 32/22.4 = 1.43 kg/m3, or 32/29 × 1.293 = 1.43 kg/m3. The mass of the molecule itself doesn’t matter; one just needs to convert the denominator from kg to m3. 1ppm=1mg/kg=1mg/（1/1.43）m3=1.43kg/m3

One should be humble and honest, and know how to respect others.

Very detailed and thorough, thank you.