A study of vertical transport and reaction of isoprene in the convective boundary layer with a second-order closure model

We have developed a one-dimensional second-order closure model to calculate the transport and chemical reactions of trace species such as ozone, nitrogen oxides, hydroxyl radicals and various organic compounds (e.g. isoprene) in the convective atmospheric boundary layer (CBL). The resulting system of partial differential equations is solved for profiles of concentrations, fluxes and scalar covariances as continuous functions of space-time. This approach allows us to resolve the vertical structure of profiles over any interval in the CBL, including using very fine resolution in the surface layer where profiles can change rapidly with height. We also developed an efficient numerical implementation, using Wolfram Mathematica, which allows us to generate large systems of coupled moment equations for an entire set of reactive species, and solve the resulting equations numerically. It requires little computer time and capacity (desktop), and it is easy to make changes in the transport and chemical parameterizations so that their impact on the resulting concentration and flux profiles can be quickly evaluated. The model has previously been used to describe the mean, flux, and scalar covariance profiles of O3, NO, and NO2. We now extend it to include isoprene, which is emitted by vegetation, and the major species with which it interacts. Since the lifetime of isoprene in the CBL is of order an hour, chemical reactivity can alter its mean concentration and flux profiles from that expected for a conserved species. We will present calculated profiles of isoprene, as well as the major species with which it reacts, and discuss the modifications in the profiles resulting from chemical reactions.