The atmosphere extends around 100km above the earth, and has a huge influence.

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  Troposphere and Stratosphere most important, chemically

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  90% of molecules in Troposphere (density decreases with height)

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  Temperature gradient throughout atmosphere

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  Gases mix well in Troposphere, poorly in Stratosphere

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    Due to direction of temperature gradient

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    Hot gases rise, cold gases fall in Troposphere

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      Not possible in Stratosphere due to reverse gradient