# Indoor Air Quality Assessment in Grocery Stores
## 2 Materials and Methods
### Monitoring Campaign  
The MBs were placed in pre-determined locations in each GS, namely, the register, the fruits and vegetable area, or the storage area. The monitoring campaign took place between November 2021 and February 2022. The MBs were placed in each grocery store at a height of around 1.20 m for a period of 2 to 5 days. The placement and number of monitoring boxes allocated to each store were determined by the size of the GS and the existence of a storage area. Table S2 provides the location of each MB within the studied GSs.  
According to the Instituto Portugues do Mar e Atmosfera (IPMA), November had a mean air temperature of 11.2 \(\pm\) 1.2 \({}^{\circ}\)C (ranging from 5.8 \(\pm\) 2.1 \({}^{\circ}\)C to 16.6 \(\pm\) 0.3 \({}^{\circ}\)C), December had a mean air temperature of 11.7 \(\pm\) 1.2 \({}^{\circ}\)C (ranging from 7.7 \(\pm\) 1.6 \({}^{\circ}\)C to 15.7 \(\pm\) 1.8 \({}^{\circ}\)C), January had a mean air temperature of 9.7 \(\pm\) 0.8 \({}^{\circ}\)C (ranging from 4.0 \(\pm\) 0.5 \({}^{\circ}\)C to 15.3 \(\pm\) 2.2 \({}^{\circ}\)C), and February had a mean air temperature of 11.3 \(\pm\) 1.3 \({}^{\circ}\)C (ranging from 5.3 \(\pm\) 0.3 \({}^{\circ}\)C to 17.4 \(\pm\) 3.0 \({}^{\circ}\)C) [25; 26; 27; 28].  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Monitoring** & **Parameter** & **Unit** & **m** & **b** & **R\({}^{2}\)** & **RMSE** & **Range REF** & **\(n\) Points** &
\begin{tabular}{c} **Ratio** \\ **MB/REF** \\ \end{tabular} \\ \hline \multirow{5}{*}{AirQ1} & PM\({}_{2.5}\) & \(\upmu\)g.m\({}^{-3}\) & 3.5262 & 3.5003 & 0.977 & 61.2 & 4.2–382.2 & 763 & 0.26 \\  & PM\({}_{10}\) & \(\upmu\)g.m\({}^{-3}\) & 3.4709 & 1.6958 & 0.973 & 56.7 & 4.2–383.0 & 884 & 0.28 \\  & CO\({}_{2}\) & ppm & 1.0389 & \(-\)12.427 & 0.986 & 37 & 369–2549 & 1336 & 0.98 \\ (A) & VOCs & ppb & 0.4529 & \(-\)191.69 & 0.426 & 535.7 & 60.0–139.3 & 278 & 6.77 \\  & T & \({}^{\circ}\)C & 1.1421 & \(-\)4.4108 & 0.936 & 1.5 & 15.0–31.7 & 1418 & 1.07 \\  & RH & \% & 1.2837 & \(-\)9.0300 & 0.927 & 4.7 & 36.1–69.6 & 1430 & 1.09 \\ \hline \multirow{5}{*}{AirQ2} & PM\({}_{2.5}\) & \(\upmu\)g.m\({}^{-3}\) & 2.0717 & 1.3919 & 0.993 & 26.5 & 3.0–198.1 & 1206 & 0.46 \\  & PM\({}_{10}\) & \(\upmu\)g.m\({}^{-3}\) & 2.0024 & 0.9004 & 0.992 & 23.1 & 3.0–190.3 & 1289 & 0.48 \\  & CO\({}_{2}\) & ppm & 1.0259 & \(-\)78.503 & 0.987 & 70 & 369–2549 & 1461 & 1.11 \\ (B) & VOCs & ppb & 0.3484 & \(-\)63.02 & 0.635 & 355.2 & 60.0–122.0 & 281 & 4.82 \\  & T & \({}^{\circ}\)C & 1.144 & \(-\)3.9528 & 0.931 & 1.1 & 15.0–31.7 & 1470 & 1.04 \\  & RH & \% & 1.2346 & \(-\)8.2152 & 0.931 & 3.6 & 36.1–69.6 & 1470 & 1.06 \\ \hline \multirow{5}{*}{AirQ3} & PM\({}_{2.5}\) & \(\upmu\)g.m\({}^{-3}\) & 1.8409 & 1.7687 & 0.992 & 21.2 & 3.0–176.2 & 1246 & 0.50 \\  & PM\({}_{10}\) & \(\upmu\)g.m\({}^{-3}\) & 1.7658 & 1.2891 & 0.992 & 16.8 & 3.0–164.7 & 1267 & 0.53 \\ \cline{1-1}  & CO\({}_{2}\) & ppm & 0.9917 & \(-\)128.65 & 0.982 & 139 & 369–2549 & 1471 & 1.24 \\ (C) & VOCs & ppb & 0.3138 & \(-\)134.26 & 0.677 & 581.2 & 60.0–110.0 & 238 & 7.87 \\ \cline{1-1}  & T & \({}^{\circ}\)C & 1.0334 & \(-\)1.3159 & 0.949 & 1.0 & 15.0–31.7 & 1467 & 1.03 \\ \cline{1-1}  & RH & \% & 1.1233 & \(-\)3.2509 & 0.938 & 3.1 & 36.1–69.6 & 1473 & 1.06 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Intercomparison results between MBs and the reference equipment for all the studied parameters. RMSE stands for root mean square error (assessed as described elsewhere [24]). Range REF stands for the range of the pollutant as measured by the reference equipment (REF).