# Exposure to NO\({}_{2}\) and PM\({}_{2.5}\) While Commuting: Utility of Low-Cost Sensor
## 4 Discussion
### Analysis of Exposure According to Commuting Patterns  
Figure 6 summarizes PM\({}_{2.5}\) exposure associated with different modes of transport across various global cities, highlighting clear spatial and contextual differences. In several locations, such as Salt Lake City (USA), Barcelona (Spain), and Hamilton (Canada), the lowest concentrations were recorded inside private cars with closed windows, while the highest exposures occurred during walking or cycling. In cities like Bogota (Colombia) and Vellore (India), pedestrians and cyclists experienced the greatest exposure, likely due to direct proximity to traffic emissions. Only in European cities such as Milan (Italy) and during our study in Gliwice was seasonal variation presented--exposure levels were notably higher during the heating season compared to non-heating periods. These examples demonstrate that the mode of transport, local infrastructure, and seasonal factors substantially influence personal exposure to PM\({}_{2.5}\) in urban environments.  
Figure 7 summarizes NO\({}_{2}\) exposure levels associated with different modes of transport in three urban locations: Montreal (Canada), Milan (Italy), and our study in Gliwice (Poland). Across all cases, individuals traveling by vehicle (V) experienced the lowest NO\({}_{2}\) concentrations, while higher exposures were generally observed among those walking (W) or cycling (B). In Montreal, the exposure ranking was V \(<\) C \(<\) B, suggesting a clear protective effect of enclosed vehicle environments. Similarly, in Milan, exposure during the heating season followed the pattern C \(<\) B \(<\) W, whereas, in the non-heating period, car use offered the greatest protection (C \(<\) W \(<\) B). In Gliwice, seasonal differences were again apparent: during the heating season, cyclists were the most exposed (B \(<\) W \(<\) C), while in the non-heating period, the highest concentrations were observed among pedestrians (W \(<\) B \(<\) C). These findings emphasize that mode of transport, seasonal conditions, and the degree of  
Figure 6: Comparison of PM\({}_{2.5}\) exposure concentrations (\(\mu\)g/m\({}^{3}\)) and inhaled doses (\(\mu\)g per km or per trip) by different modes of transport, based on location-specific data from this and other studies.  
physical enclosure significantly affect NO2 exposure in urban settings, with walking and cycling consistently associated with increased concentrations relative to vehicle travel.  
The individual analysis of the participants' exposure patterns provided additional insights. Person 1 (male participant), commuting from the suburbs to the city center, showed significant variations in NO2 exposure between transport modes, with the highest levels observed while walking. This could be attributed to prolonged exposure in high-traffic urban environments. Conversely, person 2 (female participant), who mainly traveled within the city center, exhibited no significant NO2 differences between modes but showed higher PM2.5 exposure when cycling or using a vehicle. These differences underscore the impact of route characteristics, urban infrastructure, and traffic conditions on personal exposure.