I'm a chemistry layperson looking for chemistry expertise regarding atmosphere composition.

Earth's atmosphere is oxidizing, but it was somewhat reducing in the distant past before photosynthetic life developed. Venus has an acidic atmosphere primarily composed of carbon dioxide which includes clouds of sulfuric acid. Some planetary bodies have reducing atmospheres containing hydrogen sulfide or carbon monoxide.

How do redox and acid-base reactions interact in the context of planetary atmosphere compositions? Specifically, what combinations of reducing/oxidizing and acidic/basic atmospheres are possible? Are there other planetary atmosphere types that should be considered when categorizing them?

Quick terminology question: Does it even make sense to refer to an atmosphere as acidic or basic?


We most certainly can call atmospheres acidic or basic. Put some quicklime, or even magnesia, in our air and you see that it undergoes an acid-base reaction with acidic materials (water vapor, carbon dioxide) in our atmosphere. Over time, our weakly acidic atmosphere gradually dissolves in water and then reacts with alkali and alkaline earth metal silicates too, turning rock into clay.

Our atmosphere became acidic as it picked up oxygen, which is indeed an "acid former" through the volatile (thus atmospheric) compounds it forms with several nonmetals. In contrast, the gas (or at least, clouds therein) on the giant planets contain some ammonia and would appear basic if we brought typical Earth chemicals there.

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