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

Final Report — September 2004
Comparing SO 2 emissions from all sources other than the Carbón power plants, the BRAVO
estimate (225,000 tons/year) disagreed with the estimate of the Mexican Ministry of Energy
(398,000 tons/year), a ratio of about 1.8.
Incorrect boundary conditions for CMAQ could result from the overestimation of SO 2
and sulfate by REMSAD along the boundaries of the CMAQ domain, as identified in
Section 9.9. Specifically, compared to measurements, REMSAD overestimated sulfate
concentrations along the CMAQ domain boundary by approximately 40% and SO 2
concentrations there by a factor of about 3.8.
For one model configuration that explored the combined effects of these factors,
emissions of SO 2 and sulfate within the Mexican portion of the CMAQ domain (except
emissions from the Carbón power plants) were increased by a factor of two and the
REMSAD-based lateral boundary conditions for SO 2 and sulfate were scaled with CASTNet
and IMPROVE observations. When these adjustments were made, model performance for
SO 2 and sulfate improved over that of the preliminary base case simulation, with bias and
error reduced for both species throughout the BRAVO network, as shown in Table 9-17. In
the end, this simulation was selected as the CMAQ-MADRID base case simulation and
served as a basis for estimating the source attributions that will be presented in Chapter 11. 1
Consequently, the rest of the discussion below will address the performance of this
configuration of CMAQ-MADRID.
Table 9-17. Network-average CMAQ-MADRID SO 2 and fine SO 4 2– performance statistics for
preliminary and final base case simulations.
Statistic Weekly SO2 24-hour fine SO4 2–
Units
Prelim.
Base
Case
Final Base
Case
Prelim.
Base
Case
Final Base
Case
Observed mean µg/m 3 1.48 1.48 3.1 3.1
Simulated mean µg/m 3 1.74 1.61 4.67 3.97
Coefficient of
Determination (r 2 )
0.45 0.46 0.47 0.47
Mean bias µg/m 3 0.26 0.12 1.57 0.87
Mean error µg/m 3 0.69 0.60 2.24 1.67
Mean Normalized Bias % 48 40 57 37
Mean Normalized Error % 71 64 82 65
Fractional Bias % 15 20 18 8
Fractional Error % 44 43 54 47
RMS error µg/m 3 1.09 0.97 3.58 2.65
1 The CMAQ-MADRID base case simulation covers the time period July 2 – October 28, which is
slightly shorter than the period of the REMSAD simulation. This causes slight variations in statistical
data based on observations, e.g. mean observed concentrations, compared to the corresponding values
in the tables shown in Section 9.9 in conjunction with the evaluation of REMSAD performance.
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