# Ventilation Systems and Their Impact on Nanoparticle Concentrations in Office Buildings
## 3 Results
### Diurnal Cycles of Nanoparticle Concentrations and the Ventilation Flows  
The NP concentrations and the simultaneous ventilation flows in the five most characteristic buildings are presented in Figures 5-10. The buildings were chosen in order to represent buildings with: (1) variable and (2) more constant ventilation flow and (3) different distances from a busy street. Building 1 represents a newly completed building where the ventilation was not yet properly working (switched off during two working days) (Figure 5). In some cases, an increase in NP concentration can be seen after ventilation turn-on or increase in capacity. In Buildings 3 and 7, the ventilation flow was decreased during nighttime and weekends (Figures 6 and 7). Nevertheless, the effect on NP concentrations cannot be seen in Building 3, and a tendency of anticorrelation is shown in Building 7. Building 8 had sensor-controlled ventilation in the office rooms, and these systems were switched off during nighttime and weekends (Figure 8). Here, there were several days with a decrease in NP concentrations in connection with the systems being switched off, and an increase in connection with the system being switched on again (Figure 8).  
Figure 5: The NP number concentration (blue line) and the ventilation flow (orange line) in Building 1 during the heating season. The NP concentrations and the ventilation flow were measured in five-minute intervals.  
Figure 8: The NP number concentration (blue line) and the ventilation flow (orange line) in Building 8 during the heating season. The NP concentrations and the ventilation flow were measured in five-minute intervals.  
Figure 6: The NP number concentration (blue line) and the ventilation flow (orange line) in Building 3 during the heating season. The NP concentrations and the ventilation flow were measured in five-minute intervals.  
Figure 7: The NP number concentration (blue line) and the ventilation flow (orange line) in Building 7 during the heating season. The NP concentrations and the ventilation flow were measured in five-minute intervals.  
The Correlation Coefficients (Pearson) between the Ventilation Flow and the NP Concentrations at Different Size Fractions  
In order to determine the filtration efficiency at different particle size fractions, the correlation coefficients between the ventilation flows and the NP concentrations measured during the whole one-week measurement periods were calculated. These correlation coefficients are presented in Figures 11-14. The figures were selected in order to include buildings with a variable ventilation flow throughout the day and the night during the whole measurement week.  
Figure 11: The correlation coefficients (Pearson) between the ventilation flow and the NP number concentration during the one-week measurement period presented for each size fraction in Building 3 during the heating season.  
Figure 12: The correlation coefficients (Pearson) between the ventilation flow and the NP number concentration during the one-week measurement period presented for each size fraction in Building 4 during the heating season.  
Figure 13: The correlation coefficients (Pearson) between the ventilation flow and the NP number concentration during the one-week measurement period presented for each size fraction in Building 7 during the heating season.  
The correlation coefficients in Figures 11-14 were in general relatively low in the size fractions of 10-20 nm. In Figure 13 (Building 7), negative correlations were in general shown during the entire size range. Building 7 was located furthest away from a busy street (Table 2).