# Exposure to NO\({}_{2}\) and PM\({}_{2.5}\) While Commuting: Utility of Low-Cost Sensor
## 4 Discussion
### Inhaled Doses of Pollutants  
The variability in air pollution exposure across locations highlights the influence of urban air quality. Cities with high pollutant levels, such as Bogota, Colombia (130.0-176.3 ug/m\({}^{3}\) PM\({}_{2.5}\) in buses), and Vellore, India (118-150 ug/m\({}^{3}\) in buses, 174-202 ug/m\({}^{3}\) in cars), demonstrate the impact of dense traffic and industrial emissions on inhaled doses. In contrast, cities such as Salt Lake City benefit from cleaner air, leading to lower doses. In this comparison, Gliwice appears to be a city with moderate air quality. A gender-based analysis of inhaled doses demonstrated a notable disparity. During cycling, inhaled doses per kilometer showed higher mean values for the female than the male participant. The mean PM2.5 dose per kilometer was 19.8 ug/km for the female compared to 9.8 ug/km for the male participant, while the NO2 dose per kilometer was 58.7 ug/km for the female participant and 33.8 ug/km for the male participant. Several studies also provide insights into inhaled doses during cycling. In Milan, Italy, the inhaled NO2 dose varied between 12.8 ug/km in winter and 5.5 ug/km in summer, indicating strong seasonal effects. Similarly, studies in Mexico City and Vellore, India, reported higher inhaled PM2.5 doses (10.59 ug/km and 12-17 ug/km, respectively), comparable to our results from Gliwice. During traveling by vehicle, the male participant inhaled higher doses of both PM2.5 (3.3 ug/km) and NO2 (8.1 ug/km) than the female (0.6 ug/km and 2.4 ug/km, respectively). In Montreal, Canada, car users inhaled an average of 5.52 ug/km PM2.5 and 6.78 ug/km  
Figure 7: Comparison of NO2 exposure concentrations (ug/m\({}^{3}\)) and inhaled doses (ug per km or per trip) by different modes of transport, based on location-specific data from this and other studies. for bus users, whereas in Lisbon, bus passengers had a PM\({}_{2.5}\) dose of 25 \(\upmu\)g/km and car passengers 13 \(\upmu\)g/km. In Mexico City, the inhaled PM\({}_{2.5}\) dose for bus users was 5.77 \(\upmu\)g/km, while car and carsharing users had lower doses of 3.09 and 2.77 \(\upmu\)g/km, respectively. In Salt Lake City, USA, vehicle users had much lower inhaled doses, ranging from 0.2 \(\upmu\)g/km in buses to 0.46 \(\upmu\)g/km in cars without air conditioning. In comparison, Montreal car users inhaled an average of 5.52 \(\upmu\)g/km of PM\({}_{2.5}\), while bus users inhaled 6.78 \(\upmu\)g/km. In Lisbon, bus passengers received a PM\({}_{2.5}\) dose of 25 \(\upmu\)g/km, whereas car passengers received a dose of 13 \(\upmu\)g/km. In Mexico City, the inhaled PM\({}_{2.5}\) dose for bus users was 5.77 \(\upmu\)g/km, while car and carsharing users had lower doses of 3.09 and 2.77 \(\upmu\)g/km, respectively. In Salt Lake City, USA, vehicle users had much lower inhaled doses, ranging from 0.2 \(\upmu\)g/km in buses to 0.46 \(\upmu\)g/km in cars without air conditioning. In the case of walking as a mode of transport, inhaled doses of both PM\({}_{2.5}\) and NO\({}_{2}\) were significantly higher than for bicycle and vehicle users. In Gliwice, pedestrians inhaled the highest doses of PM\({}_{2.5}\), with the male participant averaging 30.7 \(\upmu\)g/km and the female participant 31.6 \(\upmu\)g/km. For NO\({}_{2}\), the male participant inhaled 141.3 \(\upmu\)g/km, whereas the female participant inhaled 77.9 \(\upmu\)g/km. These values indicate that walking exposes individuals to increased air pollution due to longer exposure times and direct contact with ambient pollutants. Comparisons with other cities highlight notable differences in pedestrian exposure. In Xi'an, China, PM\({}_{2.5}\) concentrations for pedestrians reached 35.4 \(\upmu\)g/m\({}^{3}\), with inhaled doses of 8.65 \(\upmu\)g/km for adults and 6.75 \(\upmu\)g/km for teenagers. In Milan, Italy, pedestrian exposure varied between high- and low-traffic areas, with PM\({}_{2.5}\) concentrations reaching up to 16.9 \(\upmu\)g/m\({}^{3}\) in winter for high-traffic zones.