Gas Concentration of SO2 from ppm to mg/Nm3.

To convert gas concentrations for environmental reporting at a cement plant, you must account for the gas's molecular weight, standard temperature/pressure conditions, and dilution from false air (oxygen correction).

Converting ppm to mg/Nm3 (Dry Basis)

Under standard-normal conditions (0°C and 101.3 kPa), the conversion depends on the molecular weight of the specific pollutant.

The standard formula is: mg/Nm3=ppmxMolecular Weight/22.41​

For SO2, the formula becomes;

SO2[mg/Nm3]=SO2[ppm]x2.86​

Correcting for Oxygen (False Air Adulteration)

Environmental regulations require emissions to be reported at a specific reference oxygen level (typically 10% in Europe or 7% in the US) to prevent plants from "fixing" high emission numbers by diluting them with ambient "false air".

The Correction Formula: Multiply the Correction Factor to account for O2 reference

Cref​=Cmeas​×[(21−O2,ref​​)/(21−O2,meas​)]

  • Cref​: Concentration at the reference O2​ level (e.g., 10%).
  • Cmeas​: Actual concentration measured by the analyzer.
  • O2,meas​: Actual oxygen percentage measured at the same time.
  • 21: The percentage of oxygen in ambient air.

Important Definitions for Reports

  • Nm3 (Normal Cubic Meter): Gas volume at 0∘C and 1 atm (760 mm Hg).

Allowable emission ranges in cement plants vary by region and kiln technology, but standard limits (calculated at 10% reference O2​) typically fall within these brackets:

Sulfur Dioxide (SO2​)

  • Pyrite-Dependent Limits...
  • Reported Ranges...

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