Simulation of Turbulent Mixing Effects on Essential NOx–O3–Hydrocarbon Photochemistry in Convective Boundary Layer

Abstract

The turbulence kinetics model (TKM) describes an overall reaction rate for microscopic mass transfer phenomenon expressed as separation intensity, Is, in a turbulent reacting flow. This study examines the effects of turbulent mixing in the convective boundary layer (CBL) on essential NOx–O3–Hydrocarbon photochemistry containing sources of NO and a surrogate reactive hydrocarbon. The modeling approach applies for all species except OH with an assumption of a photostationary steady state. The TKM results reveal principal findings as follows: (1) effects of turbulence on reaction rates lead to significant segregations throughout most of the CBL in reaction pairs NO + O3, RH + OH and NO + HO2; (2) segregations permit significantly higher concentrations of NO and RH to build up and endure in the CBL than would occur for a non-turbulent atmosphere; (3) turbulent segregation influences limit and shift the ranges of NO and O3 concentrations compared to the non-turbulent case; (4) while there are differences between the TKM results and those for a published Large Eddy simulation (LES) of the same chemical system, there are also strong similarities. Therefore, a future study remains to compare model results to observations if and when appropriately time-resolved measurements of reacting species are obtained.