## 3 Results and Discussion  
### Comparison of Sampling Locations  
Sampling locations and environments were selected to be representative of classes where series of known events are present, in addition to the availability of tools to perform the sampling (i.e., electrical connection and protection from the atmospheric events) for eight (8) consecutive hours, approximately from 9 a.m. to 5 p.m. Normally in the warehouse, emission sources are absent and air recirculation is low: This condition is indicated as \"indoor quiet.\" Occasionally, building work in the presence of extraordinary emission sources is performed: This condition is indicated as \"indoor busy.\" Direct car exhaust emissions and resuspension of fine particles are present in the garage. Uncontrollable diffuse emissions are present outdoors. All the daily patterns collected with KORA and AirVisual Pro along with the specific events that occurred during the monitoring period are reported in the Supplementary Materials (Figures S2 and S3 and Table S1). Both patterns allowed a simple and immediate evaluation of PM2.5 concentration trends, showing peaks corresponding to the presence of identified emission sources. For a detailed comparison, a one-day representative of each sampling location and environmental conditions was selected. The corresponding PM2.5 daily patterns collected with KORA are reported in Figure 2, with the identification of the most relevant emission sources (see Supplementary Materials Table S1 for the code descriptions).  
The locations have different ranges of average concentration values. The average PM2.5 baseline concentrations indoors fell in the range of 4-15 \(\mathrm{\SIUnitSymbolMicro m}^{3}\) and were clearly influenced by the presence of peaks, up to 40-45 \(\mathrm{\SIUnitSymbolMicro m}^{3}\) under busy conditions due to emissions from internal combustion engines in the warehouse. During the indoor busy condition, the occurrence of events such as a truck entering the warehouse at 9 a.m. and the following wall demolition at 11 a.m. were reflected over different duration periods, lasting the time needed for full air recirculation in the area investigated. The presence of a forced aspiration near the emission source rapidly abated PM2.5 concentrations. The average PM2.5 concentration outdoors was significantly higher (about 40-50 \(\mathrm{\SIUnitSymbolMicro m}^{3}\)) and quite constant during the day apart from sporadic events due to smokers in the proximity of the sampling device (three sharp peaks were registered between 11:16 and 12:28 a.m.). They  
Figure 2: Daily patterns of PM2.5 concentrations measured by KORA in different environments: (a) indoor busy, (b) indoor quiet, (c) outdoors, (d) garage, respectively. The labels (E: car exhausts, S: cigarette smoke, H: hammering works, C: crane movements, T: crane truck circulation, B: building and construction works, V: local forced ventilation, D: drilling work) describe the local ongoing activities (a complete list is given in Table S1).  
were not persistent and did not influence the background value, as it was to be expected in a not-confined area. The PM\({}_{2.5}\) concentration range was significantly higher with respect to the previous one, mostly due to the urban contribution, which was higher during these days, as confirmed by the official data of the Regional Agency for Environmental Protection [38] A different situation was recorded in the garage, assumed to be a semi-confined outdoor area and presenting concentrations of up to 60 \(\upmu\)g/m\({}^{3}\) with peaks corresponding to emissions from car exhausts, mostly concentrated in the early morning. These emissions increased background concentrations over a large duration of time, depending on the natural ventilation conditions.