Estimating NOx emissions from soils is still very uncertain. The effects of fast reactions involving ozone and NOx and their net effect on the measured fluxes in the surface layer constitute a critical uncertainty in improving estimates of soil-derived NOx in the upper planetary boundary layer (PBL). Here we present results for a 1-D model that includes parameterization of PBL dynamics by using a 2.5 level closure based on K-E theory and a full description of chemistry and radiation for photochemical calculations. The transport of the trace gases is calculated in the model by using turbulent eddy mixing profiles modified to account for the effect of chemical reactions, with a closure scheme derived by using assumptions similar to those in the algebraic stress model. Results for this combined model will be described and compared to observations from a month-long set of measurements obtained during the National emission of Oxidant precursors-Validation of techniques and Assessment (NOVA) campaign conducted during July-August 1996.