ozone reductions due to water vapor deposition (400 launches per year) are less than 0.01% with no apparent corridor effect. This is less than one-tenth the ozone reduction computed for the Space Shuttle (48). Similar calculations have been made for nitric oxide during atmospheric reentry, which yield globally averaged reductions of about 0.02% to 0.04% (depending on the season); the corresponding result obtained with the 1-D model if ~0.02%. It is important to note that the 2-D model simulates horizontal transport, whereas the 1-D model does not. Also, there are differences in the way in which the mean sun angle is estimated (the 1-D model uses a mean solar zenith angle that is time-invariant; in the 2-D model, the solar zenith angle is latitude- and time-dependent) and in the lower boundary conditions. In the 2-D model, it turns out that NO is efficiently transported downward into the stratosphere where it is not
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