Global Tropospheric Chemistry

摘要: The most abundant atmospheric gases, molecular nitrogen (- 78% by volume) and oxygen 21% volume), are the result of global biogeochemical processes that have operated on time scales at least several tens thousands, probably millions years. For noble such as argon 0.93% involved even longer. Because these very long lifetimes dominance large scale dynamic mixing over diffusion, volume (or molar) ratios major constituents atmosphere practically constant below 100 km altitude. photochemically more stable oxygen, it is only above this height, photochemical dissociation driven solar ultraviolet radiation becomes fast enough recombination atoms sufficiently slow to cause a significant decrease in its with height. photodissociation effective higher altitudes. However, gravitational separation important than meteorological 110 (the so-called turbopause), causing relative abundances lighter gases increase altitude, so 1000 H He gradually become dominant constituents. At altitudes compounds N2 O2 minor