## 4 Results
### Time Scaling  
For the purpose of the evaluation of the time scaling of the experiment, the LASSO regression was also applied for a period of one and a half months after the one month of the main experiment (i.e., from 14 May 2021 to 31 June 2021) to all low-cost sensors, and the results are presented in the figures below. Figure 20 shows the time series and scatter plots of the NO\({}_{2}\) noncorrected measurements of three low-cost sensors (N1, N2, N3) and reference measurements, in the time period of 14 May 2021 to 31 June 2021. Figure 21 shows the time series and scatter plots of the NO\({}_{2}\) corrected measurements of three low-cost sensors (N1, N2, N3) and reference measurements, in the time period of 14 May 2021 to 31 June 2021. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**O\({}_{3}\)**} \\ \hline
**Sensors** & **N1** & **N2** & **N3** & **N1** & **N2** & **N3** & **N1** & **N2** & **N3** \\ \hline
**Method** & \multicolumn{3}{c}{**MAD**} & \multicolumn{3}{c}{**MAE**} & \multicolumn{3}{c}{**RMSE**} \\ \hline Non-corrected & 16.21 & 19.30 & 16.16 & 19.94 & 23.18 & 21.37 & 1.52 & 1.74 & 0.10 \\ Corrected & 13.78 & 15.98 & 14.92 & 17.03 & 19.59 & 20.05 & 1.54 & 1.69 & 0.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: MAD, MAE, and RMSE methods of evaluation of O\({}_{3}\) measurements. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**NO\({}_{2}\)**} \\ \hline
**Method** & \multicolumn{3}{c}{**MAD**} & \multicolumn{3}{c}{**MAE**} & \multicolumn{3}{c}{**RMSE**} \\ \hline Sensors & N1 & N2 & N3 & N1 & N2 & N3 & N1 & N2 & N3 \\ \hline Non-corrected & 2.29 & 3.47 & 2.57 & 11.78 & 12.89 & 10.16 & 0.90 & 1.04 & 1.45 \\ Corrected & 2.34 & 1.89 & 2.60 & 12.59 & 11.78 & 12.77 & 1.05 & 1.09 & 1.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: MAD, MAE, and RMSE methods of evaluation of NO\({}_{2}\) measurements. Figure 20: Time series and scatter plots of the NO\({}_{2}\) noncorrected measurements of three low-cost sensors (N1, N2, N3) and reference measurements, in the time period of 14 May 2021 to 31 June 2021. (**a**) Time series of N1 (NO\({}_{2}\)) noncorrected and reference measurements; (**b**) Scatterplot of N1 (NO\({}_{2}\)) noncorrected and reference measurements; (**c**) Time series of N2 (NO\({}_{2}\)) noncorrected and reference measurements; (**d**) Scatterplot of N2 (NO\({}_{2}\)) noncorrected and reference measurements; (**e**) Time series of N3 (NO\({}_{2}\)) noncorrected and reference measurements; (**f**) Scatterplot of N3 (NO\({}_{2}\)) noncorrected and reference measurements. Figure 22 shows the time series and scatter plots of the O\({}_{3}\) noncorrected measurements of three low-cost sensors (N1, N2, N3) and reference measurements, in the time period of 14 May 2021 to 31 June 2021. Figure 23 shows the time series and scatter plots of the O\({}_{3}\) corrected measurements of three low-cost sensors (N1, N2, N3) and reference measurements, in the time period of 14 May 2021 to 31 June 2021. Figure 21: Time series and scatter plots of the NO\({}_{2}\) corrected measurements of three low-cost sensors (N1, N2, N3) and reference measurements, in the time period of 14 May 2021 to 31 June 2021. (**a**) Time series of N1 (NO\({}_{2}\)) corrected and reference measurements; (**b**) Scatterplot of N1 (NO\({}_{2}\)) corrected and reference measurements; (**c**) Time series of N2 (NO\({}_{2}\)) corrected and reference measurements; (**d**) Scatterplot of N2 (NO\({}_{2}\)) corrected and reference measurements; (**e**) Time series of N3 (NO\({}_{2}\)) corrected and reference measurements; (**f**) Scatterplot of N3 (NO\({}_{2}\)) corrected and reference measurements. Figure 22: Time series and scatter plots of the O\({}_{3}\) noncorrected measurements of three low-cost sensors (N1, N2, N3) and reference measurements, in the time period of 14 May 2021 to 31 June 2021.