Air Chemistry in Mixing-Limited Stable Boundary Layers: Quantifying Turbulence-Chemistry Interactions in Air Pollution Modeling

This project seeks to provide an improved understanding of turbulent transport and the chemistry of reactive trace species in the stable boundary layer of the atmosphere. The primary hypothesis is that the layered structure of the stable boundary layer, together with the nonlinear character of chemical reactions, impacts vertical fluxes and the reaction rates of many important trace gases and must be considered in the interpretation of observations and the development of air pollution models. A better understanding of stable boundary layer mixing will lead to improved predictions of severe air pollution events, especially in wintertime urban regions where persistent cold air pools can result in weak vertical mixing and a buildup of pollutants at the surface. This project will address the following scientific questions: (1) How is vertical transport of passive trace species impacted by the layered vertical structure of the stable boundary layer (SBL) with strong internal inversions? Does this structure impact the applicability of traditional eddy diffusivity models as the bulk stability of the SBL increases? (2) What impact does chemistry of trace gases have on the vertical transport in the SBL? How can we parameterize the transport of reactive species and the segregation of gases as a function of atmospheric stability? (3) How much does the simulation of air pollution chemistry in stable boundary layers improve with a better description of vertical transport and segregation? (4) How does the urban canopy alter the structure of fronts in the SBL and the effects of turbulence on the vertical transport and segregation of chemical species? The broader impacts of the project include the design of an interactive exhibition as part of UCLA’s Exploring Your Universe, an annual science festival that attracts over 10,000 visitors, including many K-12 students, to the UCLA campus. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.