A Numerical Study of the Effects of Large Eddies on Trace Gas Measurements and Photochemistry in the Convective Boundary Layer

EPA Grant Number: R825262
Title: A Numerical Study of the Effects of Large Eddies on Trace Gas Measurements and Photochemistry in the Convective Boundary Layer
Investigators: McNider, R. T. , Song, Aaron , Herwehe, Jerold A. , Biazar, Arastoo
Current Investigators: McNider, R. T. , Song, Aaron , Herwehe, Jerold A. , Norris, W. B. , Biazar, Arastoo
Institution: The University of Alabama in Huntsville
EPA Project Officer: Hahn, Intaek
Project Period: February 3, 1997 through February 2, 2000
Project Amount: $275,828
RFA: Air Quality (1996) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air


It is the purpose of this investigation to examine turbulent chemical interaction in the convective boundary specifically related to isoprene/NO ozone chemistry. First, the large scale coherent eddies in the convective boundary layer can lead to chemical structures due to incomplete averaging of the turbulent medium. This can adversely affect interpretation of observations and can potentially lead to misunderstanding of the chemical pathways. This project will attempt to use coupled Large Eddy Simulation (LES) /chemical models to define appropriate averages and in the absence of complete averaging ascribe error bars to the concentration measurements. Second, it is hypothesized that the fast chemistry associated with soprene/NO interaction coupled with the large coherent eddies in the deep convective boundary layer can produce different ozone levels if average concentration are used versus explicit treatment of the corresponding concentration fluctuations associated with the large eddies. This hypothesis of a nonlinear result is bolstered by the fact that at least three chemical regimes exist in the isoprene/NO chemistry set depending on isoprene/NO ratios. The existence of divergent solution states and fast chemistry is a requirement for nonlinear turbulent effects to be important. The study will use a large eddy simulation model coupled with various levels of chemical models from simple surrogate reaction sets to full chemistry sets. Tests using first order closure models (which assume instantaneous mixing within grid cells) will be made against the coupled LES chemical simulations. The study will also investigate the effects of coherent eddies of the convective boundary layer on the representativeness of trace measurements in the boundary layer. It should provide guidance on the required sampling times for certain trace gases based on the chemical lifetimes of the gases and an estimate of the magnitude of the error due to incomplete averaging. Finally, this project should provide a research grade coupled LES chemical model for application to a variety of air pollution problems.

Publications and Presentations:

Publications have been submitted on this project: View all 4 publications for this project

Supplemental Keywords:

RFA, Scientific Discipline, Air, Mathematics, tropospheric ozone, Atmospheric Sciences, Ecology and Ecosystems, environmental monitoring, phototchemical modeling, ambient ozone data, isoprene emission algorithm, air quality data, air sampling, air pollution models, photochemistry, atmospheric chemical cycles, chemical kinetics, atmospheric monitoring, turbulent chemical interactions, ambient aerosol particles, convective boundary layer, trace gas measurement

Progress and Final Reports:

  • 1997
  • 1998
  • Final Report