A new calculation of chemical eddy transport for several middle atmospheric tracers

We describe a new approach to calculating transport of chemically active tr acers by nonbreaking planetary waves (chemical eddy transport). This approa ch uses the horizontal displacements calculated from a planetary wave model to estimate the time variation of the photolysis rates experienced at each grid point. Me contrast our method with a previously documented approach t hat assumes linear photochemical relaxation and calculates separate diffusi on coefficients for each species. Our results are presented for five middle atmospheric tracers: O-3, NO2, NO, CO, and H-2. For O-3, greater transport into the polar region is seen around 30 km, For mesospheric NO, the increa sed exposure of polar air to UV sunlight leads to more photodissociation an d thus less net downward transport into the stratosphere. Mesospheric CO an d H-2 are less sensitive to chemical eddy transport because their chemical lifetimes are longer.