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Page 12 of 24 Luo et al. Carbon Footprints 2025, 4, 14 https://dx.doi.org/10.20517/cf.2024.53

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Table 7. Summary statistics of traffic-derived NO pollution exposure (µg/m )
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Period Mean Minimum Maximum Standard deviation
Daytime 12.62 12.31 12.75 0.15
Nighttime 6.62 6.58 6.67 0.02
Morning peak 16.00 15.83 16.14 0.10
Evening peak 18.41 18.13 18.63 0.15

Figure 4. Spatiotemporal simulation results of road traffic-related NO .
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polluted areas. On weekends, travel tends to be more flexible and discretionary, with a reduction in travel
frequency and lower concentrations of traffic-related NO pollution, thereby decreasing exposure risk.
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However, this weekday-weekend distinction is less evident at night due to the continued operation of freight
and logistics services. Nighttime travel tends to be limited in scope, and there is no significant variation in
pollution exposure between weekdays and weekends, leading to a relatively stable risk level.

Spatial variation
In this study, the mean-standard deviation classification method is employed to depict the spatial
distribution characteristics of traffic-derived NO pollution exposure risk, with an emphasis on identifying
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areas with extreme exposure values. The mean exposure level serves as a baseline, and each grid is classified
into one of four risk levels: low risk (0.5 and ≤ 1.5 SD), high risk (> 1.5 and ≤ 2.5 SD), and critical risk
(> 2.5 SD).