The effects of the subgrid scales on chemical transformations in large-eddy simulations of the convective atmospheric boundary layer (CBL) are investigated. Dynamic similarity subgrid-scale models are formulated and used to calculate the subgrid-scale covariance. The dynamic procedure allows for simulations free of parameter tuning since the model coefficients are computed based on the resolved reactant concentrations. A scale-dependent procedure is proposed that allows relaxing the assumption of scale invariance used in the dynamic similarity model. Simulation results show that both models are able to account in part for the effect of the segregation of the scalars at the subgrid scales, considerably reducing the resolution dependence of the results found when no subgrid covariance model is used. The scale-dependent dynamic version yields better results than its scale-invariant counterpart.