# Indoor Air Quality Assessment in Grocery Stores
## 3 Results and Discussions
### Particulate Matter  
Figures 6 and 7 present the mean PM\({}_{2.5}\) and PM\({}_{10}\) levels assessed in each studied location of all the GSs, respectively. Regarding PM\({}_{2.5}\), 23.1% of the 13 GSs presented mean PM\({}_{2.5}\) levels above the limit value of 25 \(\mu\)g.m\({}^{-3}\) established by Portuguese legislation [34], namely, M3, M9, and M10. Considering PM\({}_{10}\), all GSs presented mean values below the limit value of 50 \(\mu\)g.m\({}^{-3}\) established by Portuguese legislation [34]. Figure 5: VOC levels assessed in all locations of the studied GSs. The red line represents the limit value of 262 ppb established by Portuguese legislation [34]. Considering World Health Organization (WHO) air quality guidelines, which establish guideline values of 5 \(\upmu\)g.m\({}^{-3}\) and 15 \(\upmu\)g.m\({}^{-3}\) for PM\({}_{2.5}\) and PM\({}_{10}\), respectively, all the GSs presented PM\({}_{2.5}\) levels above the guideline value and only four GSs presented PM\({}_{10}\) levels below the PM\({}_{10}\) guideline value (M2, M4, M5, and M12). The variability of indoor particle levels was found to be high among the studied GSs, with mean levels of 20.2 \(\pm\) 7.3 \(\upmu\)g.m\({}^{-3}\) (ranging from 1.4 \(\upmu\)g.m\({}^{-3}\) to 278.5 \(\upmu\)g.m\({}^{-3}\)) for PM\({}_{2.5}\) and 21.3 \(\pm\) 7.2 \(\upmu\)g.m\({}^{-3}\) (ranging from 2.9 \(\upmu\)g.m\({}^{-3}\) to 279.0 \(\upmu\)g.m\({}^{-3}\)) for PM\({}_{10}\). It is important to highlight that these levels were obtained with the monitoring instruments in different locations and GSs. Sudden increases in PM concentrations indoors are typically due to indoor activities [38]. Additionally, the movement of people in these environments is high since there are always clients coming in and out of the store and, therefore, the possibility of resuspension of dust is elevated [33]. GS stores with selling areas of more than 100 m\({}^{2}\) proved to have significantly higher levels of PM\({}_{2.5}\) (24.0 \(\pm\) 10.8 \(\upmu\)g.m\({}^{-3}\)) and PM\({}_{10}\) (24.9 \(\pm\) 10.7 \(\upmu\)g.m\({}^{-3}\)) when compared with GSs with lower selling areas (PM\({}_{2.5}\): 16.5 \(\pm\) 4.8 \(\upmu\)g.m\({}^{-3}\), ANOVA: F(1,23) = 4.816, \(p\)-value = 0.039; PM\({}_{10}\): 24.0 \(\pm\) 10.8 \(\upmu\)g.m\({}^{-3}\), ANOVA: F(1,23) = 4.760, \(p\)-value = 0.040). Figure 6: PM\({}_{2.5}\) levels assessed in all locations of the studied GSs. The red line represents the limit value (LV) of 25 \(\upmu\)g.m\({}^{-3}\) established by Portuguese legislation [34] and the green line represents the air quality guideline of 5 \(\upmu\)g.m\({}^{-3}\) established by the WHO [39]. Figure 7: PM\({}_{10}\) levels assessed in all locations of the studied GSs. The red line represents the limit value (LV) of 50 \(\upmu\)g.m\({}^{-3}\) established by Portuguese legislation [34] and the green line represents the air quality guideline of 15 \(\upmu\)g.m\({}^{-3}\) established by the WHO [39]. Similar results were found in a study in classrooms in France, with mean PM\({}_{2.5}\) levels of 22 \(\pm\) 8 ug.m\({}^{-3}\), ranging from 10 to 47 ug.m\({}^{-3}\)[40]. In contrast, less-crowded environments have a lower possibility of resuspension of particles. Therefore, for example, a study in elderly care centers in Lisbon assessed lower PM\({}_{10}\) levels, ranging from 11 ug.m\({}^{-3}\) to 19 ug.m\({}^{-3}\)[33]. In relation to the influence of other GS characteristics, no other significant impacts were found on either PM2.5 or PM10. However, some studies showed that some activities in houses had peak concentrations of PM, such as during the preparation of breakfast, tea, and toast, and natural-gas burning, as well as other types of cooking [41; 42; 43]. Some retail environments have different indoor spaces within and with different associated activities, which can promote different emissions of pollutants (including particulate matter, from fine to ultrafine particles) [44].