## 3 Results  
### Dynamic Evaluation Based on RRFs  
We present the results of the dynamic evaluation of the CMAQ model with standard projection procedures (i.e., based on RRFs) that are used for model attainment demonstrations in this section. Figure 8 is a spatial plot that compares gridded CMAQ RRFs with observed RRFs at monitoring sites across the SoCAB. Over much of the SoCAB, the modeled and observed RRFs are consistent and estimate that T10 modeled day ozone increased between 2019 and 2020 with some exceptions: (1) The two monitors furthest east in the SoCAB (Banning Airport and Morongo), where both the modeled and observed RRFs agree that ozone is reduced; (2) Sites near the coast (e.g., West LA, LAX, and Compton), where the model estimates ozone increases (RRF \(>\) 1.15), while the observed RRFs decreased; (3) At five additional locations throughout the basin, where both modeled and observed changes were small to moderate but may change in the opposite direction (i.e., Crestline and Perris, where the model estimates essentially no change in the RRFs and the observed RRFs indicate a slight reduction; Azusa and Reseda, where the observed RRFs indicates no change and the model estimates a 5-10% increase; and, Fontana where observed RRF indicates a decrease of 2-5% and the model estimates an increase of 2-5%). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Selected Sites**} & \multirow{2}{*}{**AQS Number**} & \multicolumn{2}{c}{**2019**} & \multicolumn{2}{c}{**2020**} \\ \cline{3-6}  & & **NMB (\%)** & **NME (\%)** & **NMB (\%)** & **NME (\%)** \\ \hline LAX & 06-037-5005 & \(-11.8\) & 13.3 & 30.3 & 30.3 \\ Los Angeles Main & 06-037-1103 & 2.2 & 10.2 & \(-2.1\) & 10.8 \\ Azusa & 06-037-0002 & \(-10.8\) & 11.5 & \(-5.4\) & 13.2 \\ Glendora & 06-037-0016 & \(-12.0\) & 12.4 & \(-13.1\) & 16.0 \\ Pomona & 06-037-1701 & 19.4 & 20.3 & \(-6.4\) & 11.7 \\ Upland & 06-071-1004 & \(-6.0\) & 12.8 & \(-8.2\) & 12.1 \\ Fontana & 06-071-2002 & \(-7.0\) & 10.3 & \(-1.3\) & 10.1 \\ Crestline & 06-071-0005 & \(-12.3\) & 15.5 & \(-10.2\) & 12.3 \\ San Bernardino & 06-071-9004 & \(-12.7\) & 16.6 & \(-12.7\) & 14.4 \\ Redlands & 06-071-4003 & \(-15.7\) & 19.0 & \(-17.6\) & 17.8 \\ \hline \hline \end{tabular}  
* Values that failed to meet the criteria are highlighted in red.  
\end{table} 
Table 2: NMB and NME for the T10 modeled days used in the RRF calculations 1. Figure 8: Comparison of CMAQ versus observed RRFs based on T10 modeled MDA8 ozone days. Thus, the only monitors that indicate a regionally consistent and substantial discrepancy between the modeled and observed RRFs are the three southwestern Los Angeles County sites near the coast (i.e., West LA, LAX, and Compton). Some potential reasons for this are discussed below. Besides these three sites, there is general agreement between CMAQ and the observed ozone responses as shown in the scatter plot in Figure 8, which compares the observed and modeled RRFs, excluding the three coastal sites discussed above. This suggests that CMAQ is broadly able to replicate the observed ozone increase between 2019 and 2020 (that include the COVID-19 emissions reductions) within the framework of the EPA's recommended ozone projection procedures used in a modeled attainment demonstration. In general, the model response is weaker than the observed response (i.e., for monitors with the most extreme positive or negative observed responses (RRF > 1.15 and RRF < 1.0)) the modeled response is muted), and responses at individual sites may vary (R\({}^{2}\) = 0.2). An obvious difference in modeled/observed RRFs is seen in the far-right side of the scatter plot in Figure 8 for the Pomona site, where the observed ozone increase (RRF = 1.32) is much greater than the modeled ozone increase (1.04).