Boiler Emission Concentration Converter

Correct CO, NOₓ and SOₓ to a reference oxygen content, then convert between ppm and mg/Nm³.

Flue gas · Dry basis

Conversion inputs

Enter dry-basis readings. Results update as you edit.

Measured O₂ (% vol, dry)

Reference O₂ (% vol, dry)

Measured concentration unit

O₂ correction convention

Normal gas conditions: 0°C, 101.325 kPa absolute

Both pollutant readings and measured O₂ must be on a dry basis. If using mg/Nm³ input, it must already be normalized to 0°C and 101.325 kPa. Wet readings and actual-stack mg/m³ require separate moisture / temperature / pressure corrections.

Measured pollutant concentrations and results at reference O₂
Pollutant	Measured ppm	ppm at O₂ 6%	mg/Nm³ at O₂ 6%
COAs CO · 28 g/mol	Measured CO concentration	—	—
NOₓAs NO₂ · 46 g/mol	Measured NOx concentration expressed as NO2	—	—
SOₓAs SO₂ · 64 g/mol	Measured SOx concentration expressed as SO2	—	—

O₂ correction factor: —

Calculation method

C_ref = C_measured × (O₂_air − O₂_ref) / (O₂_air − O₂_measured)

mg/Nm³ = ppm × M / V_m · ppm = mg/Nm³ × V_m / M

O₂ values are volume percentages on a dry basis; M is the reporting-species molar mass in g/mol and V_m is the normal molar volume in L/mol. Intermediate results retain full precision; displayed concentrations use two decimals.

NOₓ mass is reported as NO₂ equivalent. SOₓ mass is reported as SO₂ equivalent: use this only when your measurement reports SO₂ or total SOₓ on that equivalent basis. A separate SO₃ concentration needs its own molar mass.

The example uses O₂ = 11.28%, reference O₂ = 6%, 21% air oxygen and 22.4 L/mol, matching the supplied spreadsheet: CO = 90.66, NOₓ = 168.28 and SOₓ = 39.68 mg/Nm³.

Choose the reference O₂ and reporting conditions specified for your application. This converter does not select emission limits or determine compliance.

Method references: Environment Agency — stack-emission normalization; US EPA — NOₓ reporting as NO₂.

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