Oxygen Correction Calculator
Engineering Guide · Design Calculators
Oxygen correction converts a measured emission concentration to the value it would have at a specified reference oxygen level. Excess air dilutes flue gas and lowers the measured concentration, so readings must be normalized to the same O₂ reference before sources can be compared or checked against an emission limit.
CR = CM × (21 − OR) ÷ (21 − OM)CR concentration corrected to the reference O₂, CM measured concentration, OR reference O₂ (%), OM measured O₂ (%)Cdry = Cwet ÷ (1 − W)W moisture fraction of the flue gas (e.g., 12% → 0.12). The O₂ reading is converted to a dry basis the same wayThe O₂ content of ambient air is taken as 21 or 20.9. Use the value written in the formula of the emission limit or test method you follow. The reference O₂ level differs by source category, so take it from the applicable emission limit or permit.
| Step | Calculation | Result |
|---|---|---|
| Correction factor | (21 − 12) ÷ (21 − 9) | 0.75 |
| Corrected concentration | 80 × 0.75 | 60 ppm |
NOx is measured at 80 ppm with 9% O₂, both on a dry basis, and the reference O₂ is 12%.
When more air is mixed in, the same mass of pollutant shows up as a lower concentration. Correcting to a reference O₂ level lets you compare actual emission levels regardless of dilution.
The reference O₂ for each source category is set in the applicable emission limit or permit. It can change when regulations are revised, so check the current rules and your permit conditions.
Either works. The correction only multiplies by a factor, so the result comes out in the unit you entered. To change units, use the ppm to mg/Nm³ converter.
By the Micro-one R&D Center · Last updated November 1, 2026 · All Engineering Guide pages →
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