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Page 18 of 24 Luo et al. Carbon Footprints 2025, 4, 14 https://dx.doi.org/10.20517/cf.2024.53
surfaces, such as soot-catalyzed NO oxidation, further enhance NO formation, contributing to an elevated
2
[51]
ratio .
Temporal Resolution Advantage: The national standard relies on annual averages, which overlook daily
variations. Studies have shown that midday O peaks can raise the NO /NO ratio to 0.6-0.7, while nighttime
3
2
x
values drop to 0.3-0.4. These temporal patterns are supported by monitoring data .
[52]
This broader ratio range more accurately captures the chemical complexity in high-emission, high-ozone
urban environments, justifying its adoption for policy-relevant urban air quality modeling.

Group exposure disparities
This study reveals significant disparities in traffic-related NO exposure across gender and age groups,
2
highlighting the significance of activity-path-based environmental exposure assessment in environmental
equity research.

Gender disparities
Gender-based differences in exposure to traffic pollution can be explained by the concept of the social
stratification of road networks, as proposed by the Institute of Human Geography . Urban roads, as
[53]
dynamic spaces of activity, serve both as infrastructure and public services, enabling access to various
destinations. However, travel patterns differ substantially between genders due to factors such as family
responsibilities, the division of labor, and environmental conditions, leading to gender-based segregation in
[54]
mobility patterns and, ultimately, social stratification .

Previous research has shown that women, who often bear the primary responsibility for household chores,
tend to choose jobs located closer to home. Consequently, their daily mobility is subject to various
limitations and constraints . As a result, women's travel typically involves short-distance, environmentally
[55]
[56]
friendly trips, often along urban routes that include access to public transportation . In contrast, men
generally have fewer domestic responsibilities and greater career mobility. Their longer commuting
distances lead to a preference for high-capacity urban arterials and expressways to optimize travel efficiency.

Furthermore, the division of labor contributes to occupational disparities in traffic exposure. In Shanghai,
men dominate employment in the transportation, warehousing, postal, and construction sectors.
Specifically, men account for 72% of workers in transportation-related industries and as much as 83% in
construction . Given these occupational trends and mobility behaviors, men experience greater exposure
[57]
to traffic-related pollution and are therefore more vulnerable to its health impacts.

Age disparities
Significant differences in NO exposure were also observed across age groups. Older adults experienced the
2
lowest levels of exposure across all time periods, primarily due to their limited, short-distance, and
temporally concentrated travel patterns. Their reliance on walking or cycling, along with a tendency to
remain within community-based areas, further reduced their contact with high-pollution zones such as
highways. In contrast, working-age adults (19-44 years), whose mobility is largely dictated by rigid
commuting schedules and occupational demands, faced the highest NO exposure, particularly during
2
evening peak hours when pollutant concentrations exceeded daily averages.

These exposure disparities were most pronounced during the evening peak, likely due to the diversity of
travel purposes and the wide dispersion of routes, which exacerbate inequities across age groups.