Seasonal and latitudinal variations of N2O and NOxin the stratosphere

The seasonal and latitudinal behavior of N2O and NOx in the stratosphere is investigated on the basis of their currently known natural sources and sinks by using a two-dimensional model that permits both horizontal and vertical transport processes to be incorporated along with photochemical processes. The results show that the distributions of N2O and NOx derived under the combined influences of photochemical effects and atmospheric transports are in qualitative agreement with the observed data. Since the photochemical equilibrium theory alone cannot be expected to yield realistic solutions, the model results also suggest that the parameterized transports, namely, the large-scale eddy effects and the mean meridional motions that affect the photochemical production and loss processes through redistribution, can be important in maintaining the seasonal and latitudinal variations of N2O and NOx in the stratosphere. The vertical distributions of NOx indicate that the mixing ratio increases in the stratosphere from its lower boundary value (3 ppb) by a factor of 6 in summer and 4 in winter on the average. In the meridional direction the NOx mixing ratio varies by a factor of 2, higher values occurring near the summer pole. The lower boundary condition influences the NOx concentration in the lower stratosphere, but it has a negligible effect in the middle and upper stratospheres. It is found that the NOx in the stratosphere predominantly consists of NO in the upper stratosphere, NO plus NO2 in the middle layer, and HNO3 in the lower stratosphere. The model computations on NO, NO2, and HNO3 are also in qualitative agreement with the recent measurements of these constituents in the stratosphere.