Portal de Periódicos da CAPES

The divergence of the turbulent diffusion flux in the surface layer due to chemical reactions: the NO-O3-NO2 system

1993; Taylor & Francis; Volume: 45; Issue: 1 Linguagem: Inglês

10.1034/j.1600-0889.1993.00002.x

1600-0889

Jordi Vilà-Guerau De Arellano, Peter G. Duynkerke, P. J. H. Builtjes,

Atmospheric aerosols and clouds

The concentration profiles and fluxes in the atmospheric surface layer are studied for the case that the time scales of the chemical reactions and the turbulent diffusion are of similar order. A model which includes both processes, turbulent diffusion and chemical transformations, is developed and applied to the NO-O 3 -NO 2 system. The governing equations of the model are presented in a non-dimensional way which allows a more compact and elegant formulation of the problem. The concentration and fluxes of the three chemical species are correctly calculated for the whole surface layer. The model results show that the turbulent diffusion flux diverges due to the non-equilibrium state of the chemical species. Thus, the concentration profiles of the chemical species deviate from the logarithmic profile which would be obtained for non-reactive species. The divergence of the turbulent flux of ozone is calculated with the model and compared with observations taken at Pawnee site by Zeller et al. Both show a good agreement and point out the necessity to take into account chemical reactions when calculating concentration and fluxes of chemically active species. The deposition velocities of the chemical species and the photostationary state relation, two parameters which are affected by the divergence of the turbulent flux, are calculated. The model results show a variation of deposition velocities with height, which implies a shortcoming in the classical definition of the deposition velocity based on the ratio of a constant flux to the concentration. The photostationary state relation ( R ( z )), the ratio of production and depletion of NO 2 due to chemistry, also shows a variation with height. For an upward flux of NO the model results are supported by observations, both showing an increase of R(z) towards the surface. DOI: 10.1034/j.1600-0889.1993.00002.x