Oxygen in the Atmosphere:

Partial Pressure of Oxygen

Because the air pressure changes at different elevations, the partial pressure of oxygen (PO2) changes as well.  

Compare the PO2 at the locations shown on the graph. Select each (PO2) to learn how it is calculated. Note that the percentage of oxygen molecules in the air is 21% regardless of elevation.

The ALMA antenna array is 5,000 m above sea level. How does the PO2 there compare to the PO2 closer to sea level?

Figure 5. The air pressure and the partial pressure of O2 at locations of varying elevations.
Elevation
(meters/feet) 		Location Air pressure
(mmHg) 		PO2
(mmHg)
8,849 m/29,032 ft Mount Everest, Nepal/China 253
53
PO2 = 253 mmHg × 0.21 = 53 mmHg
5,000 m/16,404 ft ALMA antenna array, Chile 405
?
PO2 = 405 mmHg × 0.21 = ?
4,302 m/14,115 ft Pikes Peak, USA 458
96
PO2 = 458 mmHg × 0.21 = 96 mmHg
2,430 m/7,972 ft Machu Picchu, Peru 575
121
PO2 = 575 mmHg × 0.21 = 121 mmHg
0 m/0 ft
Sea level
760
160
PO2 = 760 mmHg × 0.21 = 160 mmHg