## 3 Results  
### Time Series Plot 3.1 Analysis of Temporal Trends in Truck Traffic and UFP Levels  
At the simplest level, the investigation looked at simultaneous trends in truck traffic count and particle number count for the smallest particle size, assuming it would be the size most likely attributable to diesel particulate matter at the site where engine exhaust was also the most visible. Figure 2 strongly indicates there may have been a correlation for those variables alone. At Brockway Avenue and Beechurst Avenue, the particle size distribution modes were characterized by a proportion of smaller particles, with a dominant peak near 0.015 \(\upmu\)m (Figure 3). The selection of this size channel of the UFP aerosol was thus considered as a likely indicator of related truck traffic in this investigation. This suggests that a substantial fraction of the UFPs present at this location are freshly emitted nucleation-mode particles, likely originating from diesel truck emissions [47]. Thus, a considerable portion of the generated UFPs (60%) at Brockway Avenue appear to be attributable to diesel trucks (Figure 4). The F-statistics, which measured how well the model explained variance relative to unexplained variables, returned a reading of 124.82, which suggests that the model was highly significant overall with an extremely small \(p\)-value (<0.0001). As with the first site, a positive correlation was observed between truck count and UFP concentration at the Beechurst Avenue site (Figure 5). The plot illustrates a positive correlation, suggesting that an increase in truck count was associated with a rise in UFP concentration. The regression analysis indicated that, despite a lower slope at Beechurst Avenue compared with Brockway Avenue, an increase in truck traffic correlated with elevated UFP concentrations. In contrast to Brockway, where pollutant entrapment was more pronounced due to the terrain, the flatter topography at Beechurst Avenue allowed for enhanced dispersion, resulting in relatively lower peak UFP levels than Brockway Avenue (Figure 6). The results from Figures 2-4 provide a narrative on the influence of diesel truck traffic on ultrafine particle (UFP) pollution at the Brockway Avenue site. Figure 2 presents a time series analysis of truck traffic count and UFP concentrations measured at minute-level intervals. The data show that sharp increases in UFP concentration (red line) frequently coincided with peaks in truck activity (blue line), indicating a strong temporal association between vehicle presence and pollutant levels. These synchronous spikes suggest that real-time truck traffic is a proximate contributor to near-road UFP emissions, consistent with the expected emission patterns from heavy-duty diesel engines during uphill climbs. Figure 4: Linear regression relationship between truck count (x-axis) and UFP concentration (y-axis). This regression analysis model for the Brockway site’s 15.4 nm particle count (per cc) vs. truck count, accounting for variability in terrain, resulted in an R squared value of 0.6035. Figure 5: Scatter plot demonstrating the lower overall concentrations at the flatter, more open, Beechurst site and the slightly less but still statistically significant (\(p<0.0002\)) linear regression correlation between truck count and UFP concentration (15.4 nm particle count per cc). Figure 3 further substantiates the source and nature of UFFs through particle number size distributions captured during the sampling period. The bimodal distribution observed at Brockway Avenue (with geometric mean count diameters of 0.07 \(\upmu\)m and 0.016 \(\upmu\)m) reflects the emission profile typical of combustion sources, especially diesel exhaust. The smaller mode (\(\sim\)15.4 nm) corresponds to freshly nucleated particles, while the second mode (\(\sim\)70 nm) likely results from particle growth due to coagulation and condensation.