## 3 Results
### Time Series Plot 3.1 Analysis of Temporal Trends in Truck Traffic and UFP Levels
The similarity of the bimodal pattern across both terrain types suggests a consistent emission source, but the elevated concentrations and sharper modes at Brockway point toward greater accumulation due to both higher emission intensity and topographic constraints on dispersion. Figure 4 shows the statistical confirmation of this single variable relationship with a distinct upward trend, suggesting that UFP concentration rises in correlation with increased truck counts. The differences in the correlation coefficients between the two sites were concerning. Having strongly considered the possibility that the relationship might be multicastal, a multivariate analysis was therefore conducted while considering the particle size distributions (using both total and individual bin counts), the loading conditions (loaded versus unloaded), the transit times of the trucks through the sampling locations, and the associated speeds. This model quantifies the contribution of truck traffic to localized UFP levels, particularly highlighting how truck-induced emissions significantly drive the concentration of the smallest and most respirable particle fractions, which are known to deeply penetrate the alveolar regions of the lungs. The moderate-to-strong R\({}^{2}\) value implies that truck activity alone accounted for over 60% of the variation in near-road UFP levels during the monitoring period. Together, these three figures support the hypothesis that diesel truck traffic, amplified by steep terrain, is a major determinant of localized UFP pollution at Brockway. The combination of a real-time spike (Figure 2), emission-related particle size  
Figure 6: The linear regression plot shows similar slopes for both sites but potentially slight topographic and subsequent engine load impacts on 15.4 nm UFP concentrations at Beechurst (blue) and Brockway (red). profiles (Figure 3), and a strong statistical association (Figure 4) creates an argument for both the source and behavior of UFPs in this microenvironment. Analysis of Particle Size Distribution at Brockway and Bechurst Avenue Sites and Its Implication for Lung Dose Estimation Using a Deposition Model  
There is a Multiple-Path Particle Dosimetry (MPPD) model yielding estimates of lung deposition that offers a vital framework for analyzing the deposition of ultrafine particulate matter across various regions of the human respiratory system [44]. The results from Brockway Avenue and Beechurst Avenue, as indicated by their respective particle size distributions, have significant implications for inhalation exposure and potential health risks. The similarity in particle size distributions between these two locations suggests a potentially easy applicability of the UFP techniques described herein in source characterization, as well as in atmospheric transformation processes and dispersion mechanisms, all of which directly impact where and how these particles deposit within the lungs. The risk due to variation in particle size related lung deposition exposure (Figure 3) was indicated for both sites by the broader bimodal distribution, with both sites having two significant peaks, similar in size but differing in proportion, relative to the total distribution. The first peak (~15.4 nm) represents smaller, perhaps more freshly emitted and less agglomerated UFPs, likely from diesel combustion and the most likely choice for indicating the presence of diesel traffic in subsequent analyses. The second peak (~0.07 \(\upmu\)m-0.1 \(\upmu\)m) suggests the presence of larger, accumulation-mode (perhaps agglomerated) particles representing a proportionately lesser impact for Brockway Avenue (40% of total) and a greater relative impact at Beechurst Avenue (60% of total).