Local and urban scale modeling - Air Pollution Modeling and Its Application - page 37

1.8 Atmospheric Boundary Layer Modeling for
Combined Meteorology and Air Quality Systems

Jonathan Pleim 1 , Robert Gilliam 1 , and Shaocai Yu 2

1
United States Environmental Protection Agency, RTP, NC, USA

2

Science and Technology Corporation, Hampton, VA, USA

Abstract Atmospheric Eulerian grid models for mesoscale and larger applications
require sub-grid models for turbulent vertical exchange processes, particularly
within the Planetary Boundary Layer (PBL). In combined meteorology and air
quality modeling systems consistent PBL modeling of winds, temperature, humidity,
and chemical concentrations is necessary for accurate simulation of chemical
transport through the 3-d grid and accurate simulation of gas-phase and aerosol
chemistry. A recently developed PBL model, known as the Asymmetric Convective
Model version 2 (ACM2), has been designed to represent realistic turbulent trans-
port of atmospheric constituents. The ACM2 has local and non-local components
for transport in convective boundary layers. Evaluation of the ACM2 involves
comparisons to observed vertical profiles of meteorology and chemistry. For
example, simulations of the Weather Research and Forecast (WRF) model and the
Community Multiscale Air Quality (CMAQ) model are compared to vertical profiles
of potential temperature, water vapor mixing ratio, and several trace chemical
species from aircraft and balloon soundings. The modeled vertical structures of
chemical and meteorological parameters are consistent with observations.

Keywords Boundary layer, non-local closure, WRF, CMAQ

1. Introduction

Parameterizations of the Planetary Boundary Layer (PBL) are important com-
ponents in meteorology models and even more critical for air quality models where
ground-level concentrations of pollutants are largely determined by the extent of
vertical mixing. Thus, accurate and consistent simulation of the diurnal evolution
and vertical mixing of meteorological and chemical species is essential for realistic
simulation of these atmospheric variables. Simple closure for the turbulent flux
terms of the Reynolds averaged equations, such as eddy diffusion, are reasonable
when the scale of the turbulent motions is smaller than the vertical grid spacing of
the model as is usually the case in stable or neutral conditions, but these assumptions