## 3 Results
### Santa Rosa Site
#### 3.1.2 Santa Rosa 2023 Dataset  
With the addition of the two Flex monitors in late 2022, all 12 of the Santa Rosa sensors were available for the 6-month period from 1 January 2023 to 13 July 2023. Mean PM\({}_{2.5}\) values for the three monitors 4-6 were compared to the calibrated monitors 1 and 2 (Table 7). (Monitor 3 was outdoors, so sensors 3a and 3b could not be compared to the calibrated monitors 1 and 2.) For the 2023 data, the model was tested against the observed CF_1 PM\({}_{2.5}\) estimates for each of the 12 sensors to determine the parameters a, c, and d for the individual best-fit models (Table 8). The mean of those estimates is the general model to be tested. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sensor** & **N** & **a** & **c** & **d** \\ \hline
1a & 52,468 & 0.004127 & 0.093125 & \(-\)0.84448 \\ \hline
1b & 52,468 & 0.003926 & 0.111286 & \(-\)0.97701 \\ \hline
2a & 51,102 & 0.00379 & 0.12145 & \(-\)1.08068 \\ \hline
2b & 51,102 & 0.00446 & 0.09843 & \(-\)1.4993 \\ \hline
3a & 52,468 & 0.003148 & 0.103468 & \(-\)0.78551 \\ \hline
3b & 52,468 & 0.003901 & 0.111096 & \(-\)0.99718 \\ \hline
4a & 52,468 & 0.00476 & 0.08175 & \(-\)1.06733 \\ \hline
4b & 52,468 & 0.003461 & 0.12012 & \(-\)0.9171 \\ \hline \hline mean & 0.003947 & 0.105091 & \(-\)1.02107 \\ \hline SD & 0.000515 & 0.013643 & 0.218565 \\ \hline SE & 0.000182 & 0.004824 & 0.077274 \\ \hline RSD & 0.046158 & 0.045899 & \(-\)0.07568 \\ \hline RSE & 4.60\% & 4.59\% & 7.57\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Estimates of a, c, and d for individual best-fit models of CF_1 PM\({}_{2.5}\) during 2021. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Valid N** & **Mean** & **Std. Err.** & **Median** &
\begin{tabular}{c} **Upper** \\ **Quartile** \\ \end{tabular} \\ \hline mean calibrated monitors (1a, 1b, 2a, 2b) & 48,073 & 2.95 & 0.029 & 1.60 & 3.14 \\ \hline
4a pm2.5 alt CF3.4 & 52,435 & 2.94 & 0.039 & 1.37 & 2.80 \\ \hline
4b pm2.5 alt CF3.4 & 52,435 & 3.09 & 0.042 & 1.36 & 2.91 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of collocated sensors 4a and 4b to the calibrated monitors 1 and 2. PM2.5 estimates from the best-fit individual models and the general model were regressed on observed CF_1 PM2.5. Results are provided for the 12 tested sensors in Santa Rosa in 2023 (Table 9). The individual models had a mean intercept of 0.01 ug/m\({}^{3}\), a mean slope of 0.997, and a mean R\({}^{2}\) of 0.997. The general models had similar mean values, but a wider range of individual values. However, no general model failed to meet the EPA guidelines of 5 ug/m\({}^{3}\) for the intercept (range: \(-\)0.2 to +0.4 ug/m\({}^{3}\)) and between 0.9 and 1.1 for the slope (range: 0.93 to 1.08) [17]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sensor ID** & **Valid N** & **Mean** & **Std. Err.** & \
\begin{tabular}{c} **Lower** \\ **Quartile** \\ \end{tabular} & **Median** &
\begin{tabular}{c} **Upper** \\ **Quartile** \\ \end{tabular} \\ \hline
1a, 1b, 2a, 2b & 24,727 & 1.01 & 0.010 & 0.32 & 0.61 & 1.17 \\ \hline
4a & 24,727 & 1.07 & 0.011 & 0.30 & 0.61 & 1.22 \\ \hline
4b & 24,727 & 1.16 & 0.012 & 0.33 & 0.64 & 1.26 \\ \hline
5a & 24,725 & 1.06 & 0.012 & 0.29 & 0.57 & 1.15 \\ \hline
5b & 24,725 & 1.15 & 0.013 & 0.31 & 0.62 & 1.24 \\ \hline
6a & 24,725 & 1.17 & 0.013 & 0.31 & 0.62 & 1.30 \\ \hline
6b & 24,725 & 1.07 & 0.012 & 0.30 & 0.59 & 1.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Comparison of collocated monitors 4–6 to the calibrated monitors 1 and 2 in 2023 data from the Santa Rosa site.