Calculator inputs
Formula used
Dalton’s law: pCO2 = yCO2 × Ptotal when the input concentration is on a wet basis.
Dry-basis correction: pCO2 = xCO2,dry × (Ptotal − pH2O) when the reported composition excludes water vapor.
Water vapor estimate: pH2O = RH × psat(T), using a temperature-based saturation vapor pressure relation.
Gas molar concentration: n/V = pCO2 / (R × T).
Gas mass concentration: mg/L = (n/V) × MWCO2 × 1000.
Optional dissolved estimate: C = kH × pCO2(atm).
Use wet basis for measured humid streams. Use dry basis for analyzer values already corrected for moisture removal.
How to use this calculator
- Enter the total system pressure and choose its unit.
- Provide the CO2 amount as ppm, percent, or fraction.
- Select whether your composition is reported on a wet or dry basis.
- Enter gas temperature and decide whether the stream is dry or humid.
- For humid gas, choose automatic humidity correction or enter water vapor pressure manually.
- Pick the output unit, then calculate to view results above the form.
- Download the result summary as CSV or PDF when needed.
Example data table
| Total pressure | CO2 input | Basis | Gas state | Temperature | Humidity setting | Calculated pCO2 |
|---|---|---|---|---|---|---|
| 101.325 kPa | 400 ppm | Wet | Humid | 25 °C | 50 % RH | 0.04053 kPa |
| 1.2 atm | 5 percent | Dry | Humid | 30 °C | 80 % RH | 5.90969 kPa |
| 760 mmHg | 0.08 fraction | Wet | Dry | 20 °C | Ignored | 8.106 kPa |
| 2 bar | 12000 ppm | Dry | Humid | 40 °C | 7.4 kPa | 2.3112 kPa |
FAQs
1. What is CO2 partial pressure?
CO2 partial pressure is the share of total pressure contributed by carbon dioxide alone. Dalton’s law treats each gas component as contributing independently to the overall mixture pressure.
2. When should I use dry basis?
Use dry basis when your instrument reports CO2 after removing water vapor mathematically or physically. The calculator then multiplies the dry fraction by dry gas pressure, not total pressure.
3. Why does humidity lower actual pCO2?
Water vapor occupies part of the total pressure. For a dry-basis composition, the available dry gas pressure becomes smaller, so the actual wet-stream CO2 partial pressure is reduced.
4. Can I enter ppm values?
Yes. The calculator accepts fraction, percent, and ppm. It converts the selected concentration unit into a mole fraction before applying pressure and humidity corrections.
5. What does the gas-phase mg/L result mean?
It is the mass concentration of CO2 in the gas phase, estimated from the ideal gas law at the chosen temperature. It is not a dissolved-liquid concentration unless Henry’s law is used.
6. What is the Henry constant field for?
It estimates dissolved CO2 concentration from the calculated CO2 partial pressure. Leave it at zero if you only need gas-phase results, or enter a suitable value for your system.
7. Does the water vapor estimate depend on temperature?
Yes. Saturation vapor pressure rises strongly with temperature. That is why the same relative humidity gives a larger water vapor correction at warmer conditions.
8. Which pressure unit should I choose?
Choose the unit that matches your instrument or report. The calculator converts internally to kPa, then displays results in your selected output unit for easier comparison.