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How to use this calculator
- Select the calculation mode matching your reporting task.
- Enter values using one consistent wet, dry, or reference basis.
- Choose molecular weight, temperature, pressure, and required units.
- Calculate, then review formulas, assumptions, warnings, and converted values.
- Use CSV, PDF, print, or copy controls for records.
Example data
| Task | Example input | Expected approach |
|---|---|---|
| ppmv to mg/Nm³ | 100 ppmv as NO₂ | Use molecular weight, pressure, and temperature. |
| Wet to dry basis | 100 ppmvw, 10% moisture | Divide by 0.90 to obtain ppmvd. |
| Oxygen correction | 100 ppm at 8% O₂ | Correct to the selected reference oxygen. |
| Mass-emission rate | 150 mg/Nm³ and 10,000 Nm³/h | Multiply concentration by gas flow. |
| SCR efficiency | 300 ppm inlet, 30 ppm outlet | Calculate simple or flow-corrected removal. |
| Annual emissions | 1 kg/h, continuous operation | Multiply by annual equivalent operating hours. |
NOx reporting notes
NOx may be reported as actual NO, actual NO₂, or NO₂-equivalent. These bases are not interchangeable without a molecular adjustment. Always display the selected pollutant basis beside results.
Wet and dry concentrations describe different gas volumes. Oxygen corrections also require matching moisture bases. Convert every compared value onto one consistent reporting basis.
Normal and standard volumes depend on stated reference conditions. The calculator shows temperature and absolute pressure used. Regulatory reports should follow the applicable prescribed conditions exactly.
Frequently asked questions
1. What does NOx mean?
NOx commonly represents nitric oxide and nitrogen dioxide. Reporting rules may define it more specifically. Confirm the required pollutant basis before converting values.
2. Why is NOx often reported as NO₂?
A common reporting convention expresses total NOx as NO₂-equivalent. This gives one consistent molecular basis. Mass values need the correct molecular-weight adjustment.
3. Can I add NO and NO₂ ppm values?
You can add them when both use identical volume bases. Temperature, pressure, moisture, and oxygen references must match. Then convert total ppm using the chosen reporting basis.
4. What is the difference between ppmv and mg/Nm³?
ppmv is a molar volume ratio. mg/Nm³ is mass per referenced gas volume. Molecular weight and reference conditions connect both units.
5. What does dry basis mean?
Dry basis excludes water vapor from the gas volume. Wet basis includes the measured moisture fraction. Moisture correction can significantly change reported concentrations.
6. Why correct NOx to reference oxygen?
Excess air can dilute measured pollutant concentrations. Oxygen correction normalizes results to a selected reference level. This supports consistent comparison between operating conditions.
7. Which molecular weight should I use?
Use 30.0061 for NO and 46.0055 for NO₂. Total NOx is often reported using 46.0055. Follow the applicable reporting requirement.
8. How is mass-emission rate calculated?
Convert concentration into mass per gas volume first. Convert gas flow into matching volume per time. Multiply both values and convert the final mass unit.
9. When should flow-corrected efficiency be used?
Use it when inlet and outlet gas flows differ. Concentration-only efficiency may then misstate actual removal. Flow correction compares inlet and outlet mass rates.
10. Can this calculator prove regulatory compliance?
No calculator alone proves compliance. Permits may specify methods, averaging periods, and reference conditions. Use approved procedures and qualified professional review.
11. How accurate are annual emission estimates?
Accuracy depends on representative mass rates and operating schedules. Startup, shutdown, bypass, and control availability also matter. Use measured operating data whenever available.
Disclaimer
This calculator provides engineering estimates and educational conversions. Regulatory reporting must use the exact method, reference conditions, F-factor, molecular basis, and averaging procedure required by the applicable permit or standard.