Environmental Engineering Reference
In-Depth Information
break down in the convective boundary layer (CBL) where convective eddies
often form in the atmospheric surface layer and rise through the entire depth of the
CBL. Under such conditions, vertical fluxes can be counter to local gradients.
To account for such large-scale transport, several models have been developed to
include non-local components. Many of these models, which are commonly used
in meteorology models, are based on gradient adjustments that are parameterized
according to the surface heat flux. Thus, these models are most valid for modeling
heat fluxes and are not easily adapted for chemical transport modeling. The Asym-
metric Convective Model version 2 (ACM2) is a hybrid model that combines local
and non-local components for comprehensive treatment of all stability conditions.
However, unlike the gradient adjustment schemes, the ACM2's non-local component
is equally valid for any atmospheric quantity because it is a simple transilient
matrix scheme that describes the mass flux exchange between non-adjacent grid
layers. The basic formulation, 1-D testing against large eddy simulations and field
experiments, and evaluation within a mesoscale meteorology model are described
in detail by Pleim (2007a, b). This paper provides preliminary evaluation of com-
bined meteorology and air quality modeling using the ACM2 in the Weather
Research and Forecast (WRF) and Community Multiscale Air Qualilty (CMAQ)
models based on field data from the Texas Air Quality Study 2 (TexAQS II).
2. Modeling
The Advance Research WRF (ARW) version 3 was run for the TexAQS II period
(August 1-October 15, 2006) with 12 km grid cell size and 34 vertical layers on a
domain that covers the eastern 2/3 of the continental US. The WRF simulations
include the Pleim-Xiu LSM and the ACM2. Details of the model configuration
and a comprehensive model evaluation are presented by Gilliam and Pleim (2009).
WRF model simulations were used to drive CMAQ modeling for the same period.
Note that these air quality simulations are considered preliminary because they do
not yet include the more detailed emission inventory for Texas that has been
prepared by the Texas Commission on Environmental Quality. To ensure con-
sistency between meteorology and air chemistry, the CMAQ was configured to
use the ACM2 for turbulent transport of chemical species and to use land surface
parameters from the PX LSM for calculation of chemical dry deposition.
3. PBL Heights
The TexAQS II field experiment included eleven radar wind profilers in East
Texas during the study period. Reliable techniques have been developed to estimate
the PBL height for daytime hours from the radar raw data (Bianco et al., 2008).
These derived PBL height data have been paired in time at each profiler site with
