Development and Application of a Two Dimensional Atmosphere-Ocean Transport Box Model to CCl3F and CCl2F2

We have used a box model approach to construct a coupled two-dimensional atmosphere-ocean transport model with pseudo-chemistry. The model can be run to produce concentrations if sources are known, or to compute sources if concentrations are known. The underlying mathematical structure allows the model to be efficiently run with output that is readily comparable to observations. With the box model method we write and solve the continuity equation in each box. Matrix methods allow us to solve the system of differential equations analytically. This eliminates errors introduced by numerical approximation techniques. Advection and turbulence in the model are parameterized using climatological winds. Chemical sinks are represented as gas species lifetimes. Transport across the atmosphere-ocean interface is based upon the thin film model which parameterizes the transport efficiency through exchange velocities and Schmidt numbers. Physical oceanic processes such as upwelling, diffusion, and lateral exchange are included and are also parameterized. The model has been calibrated using CCl₃F as a tracer and has been validated using CCl₂F₂. The model reproduces well the time series of CFC surface concentrations from 1978-present reported by the ALE/GAGE/AGAGE group. The stratospheric CFCs profiles predicted by the model are in good agreement with observations. Concentrations in the oceanic mixed layer also compare favorably to observations. To correctly match the downturn in the CCl₃F tropospheric concentrations starting in 1990 requires a longer CCl₃F release time from polyurethane foams (PUF) than the lifetime of 20 yr typically assumed. Using a PUF lifetime of 100 yr produces results in good accordance with observations.