N2O is inert and well mixed in the troposphere but decreases rapidly with height in the stratosphere. Its mixing ratio varies little throughout the troposphere with a pole-to-pole gradient of only ~1.2 ppbv, less than a 0.5% change from its average global surface value of 315 ppbv (Khalil et al., 2002). Any significant departure from the mean indicates the presence of a local source. N2O's long lifetime allows it to enter the stratosphere, primarily through convection at tropical latitudes, where it is transported through the strong upwelling currents. Once in the stratosphere, it is mixed vertically and horizontally, and is eventually removed through photolysis:
and reaction with excited oxygen atoms
Although the relative proportions vary throughout the stratosphere, Eq. 14.2 is responsible for ~90% of the total stratospheric loss, while Eq. 14.3 accounts for the remaining 10% (Garcia and Solomon, 1994).
The limited vertical exchange between the troposphere and stratosphere reduces the effectiveness of these processes at removing N2O (Bates and Hays, 1967).
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