Atmospheric Rarefaction

Rarefaction of the atmosphere at 2249 metres

I like to remark, when back home in England, that in Mexico City the air is appreciably thinner than it is in Northamptonshire, a mere handful of metres above sea level. I feel it shows me as a "travelled man", and a "man of science". But my sense of satisfaction does not last, for a wave of panic quickly follows the wave of conceit. Can I remember, and state with confidence, by how much the atmospheric pressure reduced is in Mexico City, and how much lower is the boiling point of pure water than the familiar figure of 100.0ºC. 

In Mexico City I presumably walk more slowly than I do in Northamptonshire, or breath more rapidly; but how much more slower should I walk to avoid O₂-deficit. 

I remember, a few years ago, looking it up on the web during an earlier visit, and writing a small table in my black book of worthy-but-easily-forgotten things (28th Jan 2019). I shall look it all up again, and make some calculation. Perhaps that will fix it.

Feet above sea level	Metres above sea level	Oxygen as % (v/v) of air	Air Pressure  (mm of Hg)	Air Pressure (bar)	Boiling point pure water ºC
0	0	20.9	760	!.000	100.00
	100			0.990
1000	305		733	0.965	99.0
2000	610		707	0.9303	98.0
3000	914		681	0.896
4000	1219		656	0.863
6000	1829		609	0.801	94.0
8000	2438		564	0.742	91.9
10,000	3048		523	0.688	89.8
CDMX	2249.21		578	0.7603	92.55

 

I have interpoated (linearly) between 1829 m and 2438 m to find the standard pressure and boiling point of  water at 2249.21 m (the altitude of Mexico City). I conclude that I have to walk 24% more slowly in Mexico city, or pant gently, taking 16 breaths per minute instead of the standard 12.  

How much longer I should boil an egg is a complex matter, and is more easily solved by trial and error.