# Exposure to NO\({}_{2}\) and PM\({}_{2.5}\) While Commuting: Utility of Low-Cost Sensor
## 3 Results
### Comparison Across Commuting Modes  
The comparison of three commuting modes (by bicycle, vehicle, and walking) during non-heating season revealed that the longest average commuting time was by vehicles (46.5 min) while walking was the shortest (20.7 min). Bicycle commuting time increased in the heating season (+4.2 min), while vehicle use was reduced (\(-\)8.8 min). However, these differences were not significantly different (\(p\) > 0.05). Analysis of the length of trips indicated that only in the case of bicycle trips was a significant difference between the heating (5.6 km) and non-heating (3.6 km) seasons observed. Figures 2 and 3 present the direct comparisons between concentrations of NO\({}_{2}\) and PM\({}_{2.5}\) during heating and non-heating seasons for three travel modes based on the average concentration over a single trip. The result of the Kruskal-Wallis test (\(p\) = 0.480) showed no statistically significant differences in NO\({}_{2}\) levels between groups (bicycle, vehicle, or walking). During the heating season, the mean concentrations of NO\({}_{2}\) recorded while traveling by bicycle, walking, and by vehicle were 28.1, 33.0, and 34.8 \(\mu\)g/m\({}^{3}\), respectively, with the mean concentration increasing in the order: bicycle < walking < vehicle (median values 19.2, 33.1, and 32.8 \(\mu\)g/m\({}^{3}\). In contrast, during the non-heating season, the mean concentrations followed the order: walking < bicycle < vehicle, with mean values of 21.4, 22.7, and 24.8 \(\mu\)g/m\({}^{3}\), and median values of 20.4, 19.9, and 20.8 \(\mu\)g/m\({}^{3}\), respectively. The lack of significant differences indicates that the choice of transport mode is not a determining factor in the NO\({}_{2}\) concentration. In the case of PM\({}_{2.5}\) concentrations, the Kruskal-Wallis test (\(p\) < 0.05) showed statistically significant differences between the groups. The highest mean rank was observed for trips made by bicycle, while the lowest was recorded for walking, suggesting that the mode of transport may influence exposure to PM\({}_{2.5}\). Vehicle users did not exhibit significantly different exposure levels compared to the other modes of transport. During the heating season, the mean concentrations of PM\({}_{2.5}\) increased in the order: vehicle (5.5 \(\mu\)g/m\({}^{3}\)) < walking (7.3 \(\mu\)g/m\({}^{3}\)) < bicycle (9.5 \(\mu\)g/m\({}^{3}\)), with corresponding median values of 2.5, 2.6, and 4.1 \(\mu\)g/m\({}^{3}\), respectively. In the non-heating season, the mean concentrations followed the order: walking (7.3 \(\mu\)g/m\({}^{3}\)) < vehicle (10.6 \(\mu\)g/m\({}^{3}\)) < bicycle (12.1 \(\mu\)g/m\({}^{3}\)), with respective median values of 2.3, 2.8, and 3.1 \(\mu\)g/m\({}^{3}\). The differences in NO\({}_{2}\) and PM\({}_{2.5}\) concentrations measured by individual sensors were not statistically significant between seasons, contrary to the stationary measurements at the Air lab and monitoring station, which showed statistically significant differences between seasons (\(p\) < 0.05). Seasonal trends were evident in the stationary monitoring data but not in the mobile sensor measurements, possibly due to variability in individual exposure patterns while moving. While traveling, personal exposure might be influenced more by local sources (e.g., traffic emissions near the route). Movement and changing surroundings may cause air pollution levels to fluctuate rapidly, making it harder to detect seasonal trends. In order to examine whether the choice of transport mode varies between the two participants, an additional analysis was conducted, considering the individual as a differentiating factor. The results of the Kruskal-Wallis test showed that person 1 (male participant) traveling from the suburbs to the city center was exposed to significantly different NO\({}_{2}\) levels between modes of transport.