Three-dimensional behavior of mixing-limited chemistry in the atmosphere

Abstract

The effect of turbulent concentration fluctuations in the near-source region on fast, second-order atmospheric reactions of the type A + B → C is investigated. The correlation term C′ AC′ B is related to the concentration variance of emitted species A, C′ A 2 . The specific reactions studied are those pertaining to NO-O 3-NO 2 chemistry. A locally one-dimensional finite element method (LOD-FEM) is used to solve the three-dimensional transport/chemistry equations. By evaluating the differences in the photostationary-stale parameter (λ = k 3 C NOC O 3 k 1C NO 2 ) , the effect of the fluctuation term, C NO′C′ O 3 , is shown to be substantial in the near-source region. The effect initially increases with downwind distance, and then decreases as diffusion and dissipation become dominant. Within the plume itself, the effects are smallest at the core of the plume and are most pronounced at the plume edges. The important dynamical parameters are the eddy diffusivity used for closure of the turbulent species transport equation and the dissipation of turbulent energy that controls the small-scale fluctuations. From a diurnal standpoint, the maximum effect is observed at around noontime, with minimal effects being observed in the early morning and late evening.