A Numerical Model for Chemical and Meteorological Processes in the Atmospheric Boundary Layer. Part I: A Model Description and a One-Dimensional Parameter Study

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  • 1 Department of Meteorology, Uppsala University, Uppsala, Sweden
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Abstract

A numerical flow model is presented for the atmospheric boundary layer, including dispersion and chemical transformations of air pollutants. The model is a three-dimensional time-dependent one for the mesoscale based on the conservation equations for mass, heat, motion, water, and chemical species. The present version is hydrostatic, with a turbulence closure of second order. Only gas-phase chemistry is included and the chemical reaction scheme used is a modified condensed version of the carbon bond mechanism.

A parameter study with a one-dimensional version of the model system is performed for the meteorological conditions of a typical summer day. Simulations with constant and diurnally varied deposition velocity are compared. The conclusion is that the difference in the surface concentration is minor. The difference in the maximum concentration between a simulation with a diurnally varied deposition velocity and a simulation with constant value equal to the maximum of the diurnally varied deposition velocity is about 1%. Other parameters affecting the results studied here are the temperature, the influence of pressure and water vapor on the rate constants, and the actinic flux. The resulting concentrations of ozone, peroxyacyl nitrate, and nitric acid are presented. The timing and the magnitude of peak concentrations of these species are sensitive to alterations in the parameters. When comparing the various simulations with a control run, the largest discrepancies are seen in the first simulation day, for the cases with higher albedo, and when deposition is included.

Abstract

A numerical flow model is presented for the atmospheric boundary layer, including dispersion and chemical transformations of air pollutants. The model is a three-dimensional time-dependent one for the mesoscale based on the conservation equations for mass, heat, motion, water, and chemical species. The present version is hydrostatic, with a turbulence closure of second order. Only gas-phase chemistry is included and the chemical reaction scheme used is a modified condensed version of the carbon bond mechanism.

A parameter study with a one-dimensional version of the model system is performed for the meteorological conditions of a typical summer day. Simulations with constant and diurnally varied deposition velocity are compared. The conclusion is that the difference in the surface concentration is minor. The difference in the maximum concentration between a simulation with a diurnally varied deposition velocity and a simulation with constant value equal to the maximum of the diurnally varied deposition velocity is about 1%. Other parameters affecting the results studied here are the temperature, the influence of pressure and water vapor on the rate constants, and the actinic flux. The resulting concentrations of ozone, peroxyacyl nitrate, and nitric acid are presented. The timing and the magnitude of peak concentrations of these species are sensitive to alterations in the parameters. When comparing the various simulations with a control run, the largest discrepancies are seen in the first simulation day, for the cases with higher albedo, and when deposition is included.

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