Basic questions - difficult answers.
Weather reports use relative humidity. At the surface of the Earth, this measure says something about the probability of rain and how comfortable you will feel.
However, for many applications what is really needed is either the mass of water in the atmosphere or the number of molecules. Since I am interested in spectroscopic analysis (the Greenhouse Effect), the number of molecules is what is important to me. Since my programs compute this value from the atmospheric pressure and water vapor expressed as the mixing ratio relative to the total pressure (expressed as ppm), that is what Water_Vapor.exe computes. This calculator is used to convert that value to mixing ratio for dry air which is what many papers use. For some applications, the difference is very large - for my purpose, it is not significant. This is because I want to understand the process, and I am not concerned with a 10% or 20% uncertainty. In this case, the difference is on the order of only 1%.
| Saturation Partial Pressure | mbar | This depends on only the temperature |
| Actual Partial Pressure | mbar | This is computed from the dew point |
| Total Pressure | mbar | This is measured |
| Mixing Ratio - Total Pressure | ppm | Actual Partial Pressure / (Total Pressure) * 10E6 |
| Mixing Ratio - Dry Air | ppm | Actual Partial Pressure / (Total Pressure - Actual Partial Pressure) * 10E6 |
| Relative Humidity | %RH | Actual Partial Pressure / Saturation Partial Pressure * 100 |
To Use - just type a value into any cell and the others will be automatically computed.