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What would the average percentage of atmospheric oxygen be after a limited thermonuclear war? Assume that before that war, like today, levels of oxygen in many large cities in North America, Mexico, Europe, and China stand at about 17%, though that's not a global average. With all the combustion during and after such a war, what would the global average percentage of oxygen be?

Posts from This Journal by “nuclear war” Tag

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( 3 comments — Leave a comment )
banner
Sep. 26th, 2017 05:27 pm (UTC)
I'm pretty sure that there aren't enough bombs in the world to change it by even a tenth of a percentage point. The earth is huge, the atmosphere is even bigger when you consider its size, and the amount of area covered by every nuclear weapon in the world, if set off side by side, with no overlapping, wouldn't cover the USA.

So if you need for there to be less Oxygen for a plot point, invent some sort of secret super-weapon that gets used and has an unintended side-effect (or maybe it was intended all along? Up to you as the author).
polaris93
Sep. 27th, 2017 06:51 am (UTC)
Oxygen in many large cities is already down to 17% or less -- due to which people are dying in record numbers due to cardiac, pulmonary, and neurological disorders (heart attacks, strokes, and related medical events connected to chronic lack of enough oxygen. Go out in the country and it may be as high as 21%, and other places it will be between 17% and 20%, depending on the season )think wildfires, etc.). And that's from normal combustion, whether internal combustion or free fire.

Look at Southern California. It's one huge fuel dump -- gasoline, kerosene, flammable material used in homes, trees and other plants of all kinds, huge concentrations of nitrogen-rich material (such as the Bandini fertilizer processing and storage works in downtown Los Angeles), asphalt, chemical plants, and on and on and on. One hydrogen bomb with a yield of 1.5 megatons detonating in the industrial zone of Los Angeles could set everything there that wasn't immediately vaporized by the initial heat of the bomb on fire, as burning material carried by the wind set fire to structures that had not initially been set on fire by radiant heat from the bomb. That would generate a firestorm that might end up gutting the entire Basin -- and firestorms suck all the oxygen in for miles around to feed themselves, causing what's left of the oxygen to be sorely depleted over an area about the size of Southern California. Without people to plant more trees and other plants to replace those destroyed in that firestorm, it could take quite awhile for plants everywhere else to liberate enough oxygen from atmospheric carbon dioxide to restore at least partially oxygen in the air over that area.

I did say "limited" thermonuclear war. Nukes would be used against Seattle, WA; Portland, OR; San Francisco, CA; Chicago, IL; New York City; Miami, FL; Washington, DC; Phoenix, AZ; and Santa Fe, NM. Europe and Russia become radioactive moonscapes, and China is hard hit by nukes and surrenders. Australia is hit by at least one H-bomb. And so on. But the total number of nuclear and thermonuclear devices used in this exchange is only about 7-8% of the 50,000-60,000 that could have been used by all.
galadrion
Sep. 27th, 2017 07:46 am (UTC)
How long after the "limited thermonuclear war"? That is a key datum, and not included in you inquiry. Immediately after, particularly after the firestorms burn out, then yes, there will be oxygen depletion in the burn zones... although it will be mitigated somewhat by the "Hungry Ghost" phenomenon (the convection mechanism driven by large-scale fires which draws in winds from all around themselves). Overall, I would guess that urban air in such zones, already sitting at around 17-20%, would probably temporarily drop, maybe as far down as 15%, but globally, the level wouldn't shift detectably. And with the increased convection driven by the "hot spots", even the combustion-driven oxygen depletion in the former urban zones would correct to closer to the global average, probably in less than a month - especially since the ongoing depletion factors (IC engines, primarily, but also industrial factors) would no longer be contributing on anywhere near the same scale.

Yes, radioactive fallout and other dangerous pollutants would be up after such an exchange, but unless you're talking about a much larger nuclear conflict than you seem to be implying, the active chemistry in the atmosphere isn't going to be altered all that much... and within a few weeks or a couple of months, any localized shifts in that chemistry are going to have settled back into equilibrium, assuming there aren't any ongoing drivers (such as the aforementioned IC engine/urban industrialization, which is what is currently depressing urban oxygen levels).

Edited at 2017-09-27 07:48 am (UTC)
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