Abstract

Nitrous oxide is an important greenhouse gas and the major source of stratospheric reactive nitrogen, an active participant in the stratospheric chemistry controlling ozone depletion. Tropospheric N 2 O abundances are increasing at nearly 0.3% yr -1 and this increase is expected to continue in the near future as are direct stratospheric NO y perturbations, for example, from aircraft. In order to test and gain confidence in three-dimensional model simulations of the stratospheric N 2 O-NO y system, a simplified photochemistry for N 2 O and NO y is developed for use in chemistry transport models. This chemical model allows for extensive CTM simulations focusing on uncertainties in chemistry and transport. We compare 3-D model simulations with measurements and evaluate the effect on N 2 O and NO y of potential errors in model transport, in column and local ozone, and in stratospheric temperatures. For example, with the three different 3-D wind fields used here, modeled N 2 O lifetimes vary from 173 to 115 years, and the unrealistically long lifetimes produce clear errors in equatorial N 2 O profiles. The impact of Antarctic denitrification and an in situ atmospheric N 2 O source are also evaluated. The modeled N 2 O and NO y distributions are obviously sensitive to model transport, particularly the strength of tropical upwelling in the stratosphere. Midlatitude, lower-stratospheric NO y /N 2 O correlations, including seasonal amplitudes, are well reproduced by the standard model when denitrification is included. These correlations are sensitive to changes in stratospheric chemistry but relatively insensitive to model transport. The lower stratospheric NO y /N 2 O correlation slope gives the correct net NO y production of about 0.5 Tg N yr -1 only when N 2 O values from 250 to 310 ppb are used. As a consequence, the Synoz calibration of the flux of O 3 from the stratosphere to the troposphere needs to be corrected to 550 ± 140 Tg O 3 yr -1. Copyright 2001 by the American Geophysical Union.