# I need an equation for calculating water/oxygen in an airmass

• TedNugget
In summary, the equation you are seeking is the ideal gas law, which can be used to calculate the number of moles of water and oxygen in a gas mixture based on pressure, volume, temperature, and relative humidity.
TedNugget
I seek an equation to determine the ratio of water molecules / O2 molecules in a mass of air ------- given density, temperature and relative humidity. (Moles H2O / Moles O2)

The volume can be any size, a cubic meter is fine. I’m just interested in the ratio.
Density can be expressed in any measure.

I would prefer temperature in F but C is fine.

Because water displaces other elements in an airmass I believe this could be complicated. Depending on how much Oxygen is displaced or how predictable its displacement is.

I seek to do this over a range of densities that match those from the psychrometric tables for %RH calculation.

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

Trivia:
I need some accuracy to then see if this has any correlation with wildland fire behavior.
Perhaps paralleling Celsius Crossover (Canadian Extreme Fire Behavior) or Fahrenheit Crossover (Southern US moisture of extinction).

Thanks

You may find this tool useful. Just play around, and change settings as you want and it should not be too hard to calculate O2 versus H2O ratio.

I believe the equation you are looking for is the ideal gas law, which states that the pressure of a gas is directly proportional to its density, temperature, and number of moles. It can be written as follows:

PV = nRT

Where:
P = pressure
V = volume
n = number of moles
R = gas constant
T = temperature

To determine the ratio of water molecules to oxygen molecules, we can rearrange the equation to solve for n, the number of moles:

n = PV/RT

Now, we can substitute in the given values for temperature and density, and use the relative humidity to determine the partial pressure of water vapor. The partial pressure of a gas is the pressure it would exert if it were the only gas present in a container. It can be calculated using Dalton's law of partial pressures, which states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of each individual gas.

So, if we know the total pressure and the partial pressure of water vapor, we can use the ideal gas law to calculate the number of moles of each gas present. The ratio of these two values will give us the ratio of water molecules to oxygen molecules.

I hope this helps and good luck with your research on wildland fire behavior.

## 1. What is the equation for calculating the amount of water in an airmass?

The equation for calculating the amount of water in an airmass is: water mass = air density x specific humidity x volume of air

## 2. How do you calculate the amount of oxygen in an airmass?

To calculate the amount of oxygen in an airmass, you can use the following equation: oxygen mass = air density x oxygen concentration x volume of air

## 3. What is the relationship between air density and water/oxygen concentration?

Air density is directly proportional to the concentration of water and oxygen in an airmass. As air density increases, so does the amount of water and oxygen in the airmass.

## 4. How do you determine the volume of air in an airmass?

The volume of air in an airmass can be calculated by multiplying the area of the airmass by its height or depth. This can be done using mathematical formulas or by using specialized equipment such as an air sampler.

## 5. Can this equation be used to calculate the amount of water and oxygen in any type of airmass?

Yes, this equation can be used to calculate the amount of water and oxygen in any type of airmass, including both atmospheric and indoor air. However, the specific values for air density, specific humidity, and oxygen concentration may vary depending on the type of airmass being analyzed.

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