# Evaluation of Different Chemical Mechanisms on O3 and PM2.5 Predictions in Alberta, Canada
## 3 Results and Discussion
### Precursors
#### 3.1.1 OH  
The atmospheric oxidation capacity is determined by the presence of OH, as it reacts with many trace species in the atmosphere. With respect to CB6R3, both SAPRC07 and RACM2 produced elevated O\({}_{3}\) levels in the summer (SAPRC07 \(\sim\)30% increase, RACM2 \(\sim\)100% increase), as shown in Figure 3a. Winter concentrations of OH preserved the same ordinal ranking as summer, albeit the O\({}_{3}\) levels were significantly lower than summer. Differences between the winter O\({}_{3}\) levels for the three models are probably not significant. Some of the reasons that can be attributed to this high OH production by RACM2 are as follows. Firstly, RACM2 produces more O\({}_{3}\) and, subsequently, generates more O atoms under photolysis, with the O atoms reacting with H\({}_{2}\)O to produce OH radicals. Secondly, the lower reaction rate of NO\({}_{2}\) + OH in RACM2 consumes fewer OH radicals from the atmosphere compared to CB6R3 and SAPRC07, as suggested by similar comparative studies between CB05 TU and SAPRC07 ([PERSON] et al., 2019; [PERSON] et al., 2019). Modelling studies comparing CB6R3 to CB05 TU in the continental U.S. show an increase in the OH produced of \(\sim\)25% for CB6R3 ([PERSON] et al., 2019), which should reduce the OH deficit in the CB models; but, nevertheless, under the conditions considered (temperature, humidity), CB6R3 produced the least OH.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Statistical Measure** & **Mathematical Expression** & \begin{tabular}{c} **Performance Benchmark** \\ **Goals** \\ \end{tabular} & \begin{tabular}{c} **Criteria** \\ \end{tabular} \\ \hline Normalized Mean Bias (NMB) (\%) & \(\frac{\sum\limits_{i=1}^{N}(\mathrm{B-O}_{i})}{\sum\limits_{i=1}^{N}O_{i}}\times 100\) & \begin{tabular}{c} MDAS O\({}_{3}<\pm 5\%\) \\ 24 h PM\({}_{2.5}<\pm 10\%\) \\ \end{tabular} & \begin{tabular}{c} MDAS O\({}_{3}<\pm 5\%\) \\ 24 h PM\({}_{2.5}<\pm 30\%\) \\ \end{tabular} \\ Normalized Mean Error (NME) (\%) & \(\frac{\sum\limits_{i=1}^{N}(\mathrm{P}_{i}-\mathrm{O}_{i})}{\sum\limits_{i=1}^{N} O_{i}}\times 100\) & \begin{tabular}{c} MDAS O\({}_{3}<15\%\) \\ 24 h PM\({}_{2.5}<35\%\) \\ \end{tabular} & \begin{tabular}{c} MDAS O\({}_{3}<\pm 25\%\) \\ 24 h PM\({}_{2.5}<\pm 50\%\) \\ \end{tabular} \\ Fractionalized Bias (FB) (\%) & \(\frac{2}{N}\sum\limits_{i=1}^{N}\left(\frac{\mathrm{P}_{i}-\mathrm{O}_{i}}{ \mathrm{P}_{i}+\mathrm{O}_{i}}\right)\times 100\) & \begin{tabular}{c} 24 h PM\({}_{2.5}<\pm 30\%\) \\ 24 h PM\({}_{2.5}<\pm 60\%\) \\ \end{tabular} & \begin{tabular}{c} 24 h PM\({}_{2.5}<\pm 60\%\) \\ 24 h PM\({}_{2.5}<75\%\) \\ \end{tabular} \\ Fractional Error (FE) (\%) & \(\frac{2}{N}\sum\limits_{i=1}^{N}\left|\frac{\mathrm{P}_{i}-\mathrm{O}_{i}}{ \mathrm{P}_{i}+\mathrm{O}_{i}}\right|\times 100\) & \
\begin{tabular}{c} 24 h PM\({}_{2.5}<50\%\) \\ \end{tabular} &
\begin{tabular}{c} 24 h PM\({}_{2.5}<75\%\) \\ \end{tabular} \\ \hline MDA8—Maximum Daily 8 h Average & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Definitions of statistical model performance evaluation measures and performance benchmarks.  
Figure 3: Comparison of Cb6R3, SAPRC07, and RACM2 predicted monthly mean values for (a) OH, (b) H\({}_{2}\)O\({}_{1}\) (SARRC07 value in Dice is very small when compared to Cb6R3 and RACM2) (c) MEY (SARRC07 and RACM2 values in Dice are very small when compared to Cb6R3), (d) PAN, (e) INO\({}_{x}\), (f) NO\({}_{x}\), (g) O\({}_{y}\).