# Exposure to NO\({}_{2}\) and PM\({}_{2.5}\) While Commuting: Utility of Low-Cost Sensor
## 4 Discussion
### Inhaled Doses of Pollutants
Similarly, NO\({}_{2}\) exposure was significantly higher in high-traffic areas (39.5 \(\upmu\)g/m\({}^{3}\) in winter) than in low-traffic zones (25.5 \(\upmu\)g/m\({}^{3}\) in winter). These results align with findings from Gliwice, where seasonal and traffic-related differences impact pedestrian exposure levels. Figure 6 summarizes the estimated inhaled dose of PM\({}_{2.5}\) across different modes of transport in selected urban areas, emphasizing the role of physical activity and ventilation rate in personal exposure. In cities such as Barcelona (Spain) and Xi'an (China), just as in our study in Gliwice, the highest doses were associated with walking or cycling, despite these modes not always corresponding to the highest ambient concentrations. This is likely due to increased respiratory rates during physical activity, which enhance pollutant uptake. In contrast, the lowest doses were generally recorded inside private vehicles with closed windows, as seen in Milan (Italy) and Salt Lake City (USA). In Bogota (Colombia) and Hamilton (Canada), cycling led to significantly higher doses, further illustrating the influence of exertion on inhaled pollutant load. These findings confirm that, beyond ambient concentrations, individual activity level and transport context are key determinants of the actual dose of PM\({}_{2.5}\) received. A summary of the inhaled dose of nitrogen dioxide (NO\({}_{2}\)) across different modes of transport in selected urban areas--Montreal (Canada), Milan (Italy), and during our study in Gliwice (Figure 7)--reveals a consistent pattern in which active modes of travel, such as walking and cycling, are associated with the highest doses. This is attributed to elevated ventilation rates during physical activity, which increases pollutant uptake regardless of ambient concentration. In Montreal, the dose ranking was C \(<\) V \(<\) B, indicating that cycling results in the highest dose. In Milan, the pattern remained consistent across seasons, with the lowest dose observed in car users and the highest in pedestrians (C \(<\) B \(<\) W). In Gliwice, sex-specific differences were noted. For the female, the ranking was V \(<\) B \(<\) W, whereas for the male, it was V \(<\) C \(<\) W. These results underline that the actual respiratory burden from NO\({}_{2}\) exposure is strongly influenced by the physiological demands of each transport mode in addition to environmental concentrations. Our findings emphasize the necessity of tailored air quality policies to reduce exposure for commuters using different transport modes. Measures such as improved ventilation in public transport, traffic management strategies, and the promotion of cleaner vehicle technologies could significantly lower inhalation doses for urban travelers. Additionally, observed gender-based differences may be attributed to variations in respiratory patterns, lung tidal volumes, and cycling speed, where women might inhale more pollutants due to lower ventilation efficiency or different exposure behaviors. However, the elevated inhaled doses among pedestrians emphasize the need for urban planning strategies to mitigate air pollution exposure. Implementing pedestrian-friendly infrastructure, increasing green spaces, and promoting low-emission zones can effectively reduce inhalation risks for city dwellers. Moreover, increasing public awareness regarding pollution exposure during walking could encourage behavioral changes, such as route selection to avoid highly polluted areas.