# Indoor Air Quality Assessment in Grocery Stores
## 3 Results and Discussions
### Discussion  
The present study presents some limitations such as: (i) the impossibility of performing measurements near the breathing zone, which would be the best approach, in order to assess human exposure; (ii) the location of the MBs, since MB had to be connected to power lines and, therefore, occasionally, had to stay lower or above the breathing zone; and \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{ID} & \multirow{2}{*}{MB} & \multirow{2}{*}{\begin{tabular}{c} **PM Concentration, C** \\ **(ug.m\({}^{-3}\))** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Time, _tj_** \\ **(h)** \\ \end{tabular} } & \multicolumn{2}{c}{\begin{tabular}{c} **Exposure to PM** \\ **(ug.m\({}^{-3}\).h\({}^{1}\))** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Potential Inhaled Dose (ug)** \\ \end{tabular} } \\ \cline{3-4} \cline{6-9}  & & \begin{tabular}{c} **PM\({}_{10}\)** \\ \end{tabular} & & \begin{tabular}{c} **PM\({}_{2.5}\)** \\ \end{tabular} & & \begin{tabular}{c} **PM\({}_{10}\)** \\ \end{tabular} & & \
\begin{tabular}{c} **PM\({}_{2.5}\)** \\ \end{tabular} & &
\begin{tabular}{c} **PM\({}_{10}\)** \\ \end{tabular} \\ \hline \multirow{3}{*}{**M10**} & **A** & 40.4 & 39.1 & 8.0 & 323.3 & 312.9 & 305.1 & 315.3 \\ \cline{2-9}  & **C** & 40.2 & 40.0 & 8.0 & 321.7 & 320.3 & 312.3 & 313.7 \\ \hline \multirow{3}{*}{**M11**} & **A** & 20.0 & 18.5 & 8.0 & 159.8 & 148.3 & 144.6 & 155.8 \\ \cline{2-9}  & **B** & 16.9 & 15.9 & 8.0 & 135.5 & 127.0 & 123.8 & 132.1 \\ \hline \multirow{3}{*}{**M12**} & **C** & 9.2 & 8.1 & 8.0 & 73.2 & 65.0 & 63.4 & 71.4 \\ \cline{2-9}  & **M13** & **B** & 17.9 & 16.9 & 8.0 & 143.4 & 135.4 & 132.1 & 139.8 \\ \hline \multicolumn{3}{l}{**Mean \(\pm\) SD**} & \multicolumn{1}{c}{\(21.3\pm 7.2\)} & \multicolumn{1}{c}{\(20.2\pm 7.3\)} & \multicolumn{1}{c}{\(170.0\pm 57.4\)} & \multicolumn{1}{c}{\(161.7\pm 58.7\)} & \multicolumn{1}{c}{\(157.7\pm 57.2\)} & \multicolumn{1}{c}{\(165.8\pm 56.0\)} \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 8: PM\({}_{2.5}\) exposure levels of workers at all studied locations of the GSs, considering a working period of 8 h.  
(iii) the lack of studies available in grocery stores did not allow a comparison of the present results with similar micro-environments. It is also important to highlight that the use of low-cost sensors in such studies relies on the performance of the sensors, their specifications, and the environmental conditions under which they are used. Despite the inter-comparison with reference real-time instruments allowing us to obtain calibration factors with R\({}^{2}\) above 0.90 (except for VOCs), which were applied afterward to the raw data, the inter-comparison procedure was done only before the monitoring campaign. However, during the monitoring campaign (which took three months), the sensors may have changed slightly in performance. Therefore, in future studies, it is important to evaluate the performance of the sensors during several moments of the monitoring campaign to understand if the calibrations should be updated from time to time. Regarding the hourly variability of IAQ parameters, this was found mainly with T and CO\({}_{2}\), as shown by Figure S2 (in the supplementary section), which provides the hourly variability of all studied parameters for the GS M4, at location B. Overall, the only air pollutant that showed levels above the limit value established by the IAQ Portuguese legislation was PM\({}_{2.5}\). Regarding comfort parameters, around half of the studied grocery stores showed relative humidity levels below the lower limit value (50%) established by Portuguese legislation. A large proportion of the indoor particles may come from indoor sources, such as cooking, cleaning, and resuspension of particles, due to the movement of the occupants.