A box model for on-line computations of diurnal variations in a 1-D model - Potential for application in multidimensional cases

Abstract

A zero-dimensional model (box model) was developed for the simulation of diurnal variations of minor constituents in the atmosphere, using a new technique well adapted to the integration of stiff ordinary differential equations. The aim of developing this code is the easy coupling with any multi-dimensional dynamical model, especially 3D models using the online time-splitting method. The integration scheme is a semi-implicit symetric method (SIS) which is twenty times faster than Gear's scheme and has a comparable accuracy for stiff problems. In a closed system, this method strictly conserves the number of atoms, avoiding the need for any corrections due to long integration. The code accepts any photochemical system as input. In a first application, the box model is coupled with a steady-state one-dimensional model, including NO Y , HO X , Cl Y , O X and Br Y families to study the effect of increases in bromine species on stratospheric ozone. To this end, the ground-mixing ratio of the source species CH 3 Br is increased from the present level 20 pptv to 100 pptv. The maximum decrease of ozone abundance then occurs at 19 km. This decrease is 9% if the expected low value of HBr concentration is assumed, but it could be reduced to 4% if the concentration of HBr is higher than expected, as recently measured. A possible explanation of the high HBr concentration is that HBr and O 3 are products of the reaction BrO+HO 2