# Calculating atmospheric partial pressure of oxygen

• GhostLineage
In summary, the partial pressure of oxygen is influenced by altitude, temperature, and relative humidity.

#### GhostLineage

TL;DR Summary
How do I calculate atmospheric partial pressure of oxygen using factors like altitude, temperature, humidity, and latitude?
I study genotype-environment associations in alpine species. I frequently see altitude as the sole predictor of partial pressure of oxygen in the literature concerning hypoxia adaptations. However, I understand that partial pressure of oxygen is also influenced by temperature, humidity, and latitude. Does anyone know of a way to calculate partial pressure of oxygen for points across a landscape using altitude, temperature, and possibly other abiotic factors? Or are the effects of other factors fairly negligible compared to altitude? Thanks!

GhostLineage said:
negligible compared to altitude?
YMMV.

Welcome to PF.

Air temperature, density, and pressure change with altitude.

To compute the partial pressure of oxygen, you need to know only two things, the pressure of the atmosphere and the fractional proportion that is oxygen. The partial pressure of oxygen is simply the product of those two parameters.

https://en.wikipedia.org/wiki/Partial_pressure

Astronuc and GhostLineage
Baluncore said:
Welcome to PF.

Air temperature, density, and pressure change with altitude.

To compute the partial pressure of oxygen, you need to know only two things, the pressure of the atmosphere and the fractional proportion that is oxygen. The partial pressure of oxygen is simply the product of those two parameters.

https://en.wikipedia.org/wiki/Partial_pressure
Thanks for your reply. I should have been more specific that I'm looking to calculate an estimate of partial pressure of oxygen for points across a landscape without already knowing the atmospheric pressure. I have lat/long, altitude, and other variables accessible from WorldClim. I see papers like this:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3852963/
where partial pressure of oxygen is inferred using altitude, but no other environmental variables (see figure 1).

But then I see sources describing how temperature and latitude affect barometric pressure, and can increase hypoxia (on the first page):
https://eu-ireland-custom-media-pro...EAEU/eSample/9780323359429-sample-chapter.pdf
They talk about how if the summit of Mt. Everest were at the same latitude as Denali, Everest would be impossible to climb without supplemental oxygen.

I'm hoping to find a nice equation out there like the one that Zhao et al. 2013 (posted above) used, but includes temperature, and maybe other factors like latitude and humidity.

You might try following/looking-at the references in the article you linked to.

There are 3 references just in the brief section "THE ENVIRONMENT OF HIGH ALTITUDE" on page 2.

Cheers,
Tom

GhostLineage
GhostLineage said:
I should have been more specific that I'm looking to calculate an estimate of partial pressure of oxygen for points across a landscape without already knowing the atmospheric pressure. I have lat/long, altitude, and other variables accessible from WorldClim.
This is the process you will need to follow.

1. Identify the atmospheric pressure at sea level, site altitude, temperature, and relative humidity, RH%.

2. Compute the site air pressure at that altitude from the standard model.
Pa = Po * ( 1 - ( Hft * 6.87535*10-6 ) )^5.2561; where Hft is the height in feet above sea level, Po and Pa are air pressure at sea level and at altitude respectively. ^5.2561 means raised to the power of 5.2561.

3. Convert the RH% to pp-H2O at the site temperature and computed air pressure. That is more of a challenge since it is based on temperature and pressure, and the units are very important.

4. Subtract the pp-H2O from the air pressure to get the dry air pressure.

5. Multiply the dry air pressure by the 0.20946 to get the pp-O2.

Now you must identify what information is available, and the units that are used.

Astronuc, hutchphd and GhostLineage
You also need to specify how precise your determination of pp-O2 needs to be.

GhostLineage
Tom.G said:
You might try following/looking-at the references in the article you linked to.

There are 3 references just in the brief section "THE ENVIRONMENT OF HIGH ALTITUDE" on page 2.

Cheers,
Tom
I tried West 1984 and it wasn't what I was looking for. Not sure about those other two, thanks for suggesting.

Baluncore said:
This is the process you will need to follow.

1. Identify the atmospheric pressure at sea level, site altitude, temperature, and relative humidity, RH%.

2. Compute the site air pressure at that altitude from the standard model.
Pa = Po * ( 1 - ( Hft * 6.87535*10-6 ) )^5.2561; where Hft is the height in feet above sea level, Po and Pa are air pressure at sea level and at altitude respectively. ^5.2561 means raised to the power of 5.2561.

3. Convert the RH% to pp-H2O at the site temperature and computed air pressure. That is more of a challenge since it is based on temperature and pressure, and the units are very important.

4. Subtract the pp-H2O from the air pressure to get the dry air pressure.

5. Multiply the dry air pressure by the 0.20946 to get the pp-O2.

Now you must identify what information is available, and the units that are used.
This is great, thanks! Do you have a source or name I can refer to in citing this equation? Since originally posting I also came across the hypsometric formula, but it doesn't include humidity (at least in the sources I saw).

I have everything needed here - temp in C, altitude in meters, and relative humidity.

hutchphd
hutchphd said:
You also need to specify how precise your determination of pp-O2 needs to be.
I'm really just looking for an index for downstream statistics, it doesn't need to be incredibly precise.

hutchphd
GhostLineage said:
This is great, thanks! Do you have a source or name I can refer to in citing this equation? Since originally posting I also came across the hysometric formula, but it doesn't include humidity (at least in the sources I saw).
http://www.scymed.com/en/smnxpr/prdpb394.htm

The formula presented here follows the “Equation of State” and the 1956 U.S. standard assumption. On August 23, 1945 in document AN-T-81, the Army-Navy published the equation that relates air pressure to altitude. That equation follows:
Pa = Po ( 1 - 6.87535*10-6Hc )5.2561

where Pa is the air pressure at altitude Hc at a given sea level pressure Po. Sea level pressure assumed to be 29.92 inches of mercury (760mmHg)

GhostLineage
hutchphd said:
http://www.scymed.com/en/smnxpr/prdpb394.htm

The formula presented here follows the “Equation of State” and the 1956 U.S. standard assumption. On August 23, 1945 in document AN-T-81, the Army-Navy published the equation that relates air pressure to altitude. That equation follows:
Pa = Po ( 1 - 6.87535*10-6Hc )5.2561

where Pa is the air pressure at altitude Hc at a given sea level pressure Po. Sea level pressure assumed to be 29.92 inches of mercury (760mmHg)
Great, thanks so much!

hutchphd

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