Abstract
A second-order modelling technique is used to investigate the influence of turbulence on chemical reactions. The covariance and variance equations for the NO-O3-NO2 system are developed as a function of the ratio of the timescale of turbulence (τ t ) and the timescale of chemistry (τCh): the first Damköhler number (τ t /τCh). Special attention is given to the calculation of the covariance between NO and O3 normalized by the product of their means, the so-called intensity of segregation (I S ). This parameter quantifies the state of mixing of two chemical species.
The intensity of segregation is calculated as a function of the flux of NO and the first Damköhler number. The model results presented illustrate the importance of taking the effect of turbulence on chemical reactions into account for higher values of the NO flux, for values of the ratio O3/NO larger than 12.5 and for values of the ratio τ t /τCH larger than 0.1. For such cases, the effective reaction rates are slower than if the chemical species are assumed to be uniformly mixed.
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Vilà-Guerau de Arellano, J., Duynkerke, P.G. Second-order closure study of the covariance between chemically reactive species in the surface layer. J Atmos Chem 16, 145–155 (1993). https://doi.org/10.1007/BF00702784
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DOI: https://doi.org/10.1007/BF00702784