Calculated results
After submission, the summary appears here above the form.
Enter your operating conditions and press Calculate NOx Conversion to view converted concentrations, oxygen-corrected values, mass flow, yearly totals, downloads, and the Plotly graph here.
NOx conversion input form
Formula used
1) ppm to concentration
mg/m³ = ppm × MW × P / (R × T)
2) Concentration to ppm
ppm = mg/m³ × R × T / (MW × P)
3) Wet and dry basis conversion
Cdry = Cwet / (1 − moisture fraction) and Cwet = Cdry × (1 − moisture fraction)
4) Oxygen correction
Corrected ppmvd = Measured ppmvd × (20.9 − O₂ref) / (20.9 − O₂measured)
5) Mass flow
kg/h = actual wet mg/m³ × wet flow m³/h ÷ 1,000,000
In this calculator, MW is the molecular weight basis for NOx, P is absolute pressure in atm, T is absolute temperature in kelvin, and R is 0.082057 L·atm/(mol·K). Standard-condition outputs use your chosen reference temperature and pressure.
How to use this calculator
- Enter the starting NOx value and choose its unit.
- Select whether you want NOx expressed as NO₂, NO, or a custom molecular weight.
- Enter actual gas temperature, actual pressure, and the standard reference conditions.
- Fill in moisture, measured dry oxygen, desired reference dry oxygen, and gas flow.
- Choose whether the entered flow is wet or dry, then add yearly operating hours.
- Press the calculate button to show converted values, mass flow, yearly totals, the graph, and download options above the form.
Example data table
| Case | Starting input | Moisture | Measured O₂ | Flow | Main result |
|---|---|---|---|---|---|
| Boiler outlet | 150 ppmv dry as NO₂ | 8% | 4% | 5,000 m³/h wet | 307.8819 mg/Nm³ dry and 0.914216 kg/h |
| Heater stack | 120 ppmv wet as NO₂ | 12% | 5% | 3,200 m³/h wet | 136.3636 ppmv dry and 0.465596 kg/h |
| Oxidizer vent | 250 mg/Nm³ dry as NO₂ | 10% | 6% | 6,000 m³/h wet | 121.7999 ppmv dry and 0.910390 kg/h |
These examples are illustrative. Site-specific sampling methods, reference conditions, and regulatory basis may change the final reportable value.
Frequently asked questions
1) Why does the calculator ask for NOx as NO₂ or NO?
The ppm value is unitless by volume, but mass concentration depends on molecular weight. Reporting NOx as NO₂ is common in permits, stack tests, and emission inventories.
2) What is the difference between wet and dry basis?
Wet basis includes water vapor in the gas stream. Dry basis removes water vapor mathematically. The dry value is higher whenever moisture is present because the dry gas occupies a smaller fraction of total volume.
3) When should I apply oxygen correction?
Apply oxygen correction when your permit, standard, or test method requires reporting at a reference oxygen level. This is common for combustion sources where dilution can change measured stack concentration.
4) Why do standard temperature and pressure matter?
Mass per normalized cubic meter depends on the chosen reference conditions. Different jurisdictions use different normal or standard states, so changing temperature or pressure changes mg/Nm³ results.
5) Can I start with a mass rate instead of a concentration?
Yes. Enter kg/h or lb/h as the input unit. The calculator uses actual wet flow, temperature, and pressure to derive an equivalent wet concentration and then converts it into the other reporting formats.
6) Why is measured oxygen entered on a dry basis?
Most regulatory oxygen correction methods use dry oxygen concentration because dry gas analysis removes water-vapor dilution. That makes the correction method more consistent across sources and sampling conditions.
7) Does this replace an official compliance method?
No. It is a calculation tool for conversions and screening. Official compliance values still depend on the approved test method, instrument calibration, sampling basis, and the governing permit language.
8) What should I check before using the exported numbers?
Confirm the molecular basis, flow basis, moisture percentage, oxygen reference, and standard conditions. Small setup differences can change reported values enough to affect permit comparisons or internal trend reviews.