(BRAVO) Study: Final Report. - Desert Research Institute

Final Report — September 2004
The CMAQ-MADRID model uses a much smaller computational domain than the
REMSAD model. As shown in Figure 8-5, this smaller domain is the primary limitation for
application of CMAQ-MADRID with the common attribution source regions defined earlier.
In order to deal with this limitation, the CMAQ-MADRID attribution sensitivity simulations
take advantage of the nesting of its domain within the REMSAD domain. As described
above (Section 8.4.3), the base case CMAQ-MADRID simulation uses observation-scaled
REMSAD concentration fields as boundary conditions. When performing a CMAQ-
MADRID attribution simulation for a specific source region, concentration fields from the
corresponding REMSAD attribution simulation are used to derive the appropriate boundary
conditions. For example, an attribution simulation for the Western U.S. removes emissions
from the Western U.S. cells in Figure 8-5 and removes the Western U.S. influence from the
concentrations throughout the boundary of the domain. In order to maintain mass balance,
the observation scaling factors used at the boundaries of the base case simulation are applied
to all attribution simulations.
Western
U.S.
Eastern
U.S.
Texas
Mexico
Figure 8-5. The CMAQ-MADRID attribution
source regions.
None of the attribution approaches exactly matches the boundaries of the set of
common source regions. However most of the boundary imperfections and differences are in
regions of low emissions density or in some cases the boundaries are at such a great distance
from Big Bend (e.g., the northern boundary differences for FMBR and REMSAD compared
with TrMB) that impacts from beyond them are not thought to be of practical significance.
The source-region boundaries within the CMAQ-MADRID domain are less immune to these
concerns because they are much nearer to Big Bend and in some locations the domain
boundary is over areas of relatively high emissions density. The use of the scaled REMSAD
results as the CMAQ-MADRID boundary conditions for the base case and the attribution
simulations is, in essence, a one-way nesting of the CMAQ-MADRID model within
REMSAD, so the REMSAD definitions of the source regions beyond its domain are also
applicable for CMAQ-MADRID attribution simulations.
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