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

signal data to examine spatial and temporal variations in PM exposure risk among different
2.5
[32]
socioeconomic groups in Shenzhen . Additionally, studies investigating exposure during commuting have
revealed that traffic congestion and longer commuting distances significantly increase pollution exposure
[33]
levels .

Exposure equity and environmental justice
The principle of environmental justice asserts that all individuals, regardless of socioeconomic status, should
have equitable access to public resources and share an equal burden of the health impacts resulting from
environmental degradation . Originating in the United States in the 1980s, the concept initially focused on
[34]
the spatial inequities associated with the placement of polluting facilities in marginalized communities,
exemplified by the 1,982 protests against the siting of a hazardous waste landfill in Warren County, North
Carolina . Over time, this framework has expanded to encompass disparities in air quality, access to
[35]
transportation, flood risk management, and other dimensions, evolving into a critical interdisciplinary field
that bridges social geography and public health.

A major subfield of environmental justice research is the assessment of equity in air pollution exposure,
which seeks to identify disparities in exposure levels among different sociodemographic groups (e.g., by
gender, age, income, ethnicity). Extensive evidence confirms that low-income and less-educated
populations, along with children, the elderly, and ethnic minorities, often bear a disproportionate share of
pollution exposure risks . For example, studies in the United Kingdom have revealed a “Matthew effect” in
[36]
air quality improvement policies, whereby middle- to high-income groups - who typically have lower
baseline exposure - benefit disproportionately, while high-exposure, impoverished communities suffer
unintended consequences during policy transitions. This trend risks deepening regional resource allocation
conflicts and perpetuating environmental injustices.

However, current research on exposure equity is largely concentrated in developed nations, particularly the
United States and the United Kingdom, with relatively limited attention to developing countries such as
China. Amid China’s rapid urbanization and industrialization, air pollution from transportation, ports, and
construction has become increasingly intertwined with daily human activity, intensifying exposure
disparities across social groups. Consequently, examining group-specific disparities in traffic-related
pollution exposure in Chinese cities is now a critical pathway for promoting health equity and enhancing
environmental governance.

METHODS
Case study
Baoshan District, located in the northeastern part of Shanghai, falls under the city’s jurisdiction. Positioned
at the confluence of the Yangtze River, Huangpu River, and Yunzaobang, the district features a 46.5-
kilometer-long shoreline. Its port area connects to more than 400 ports across 164 countries and regions. As
a key “waterway gateway” for Shanghai, Baoshan features an integrated transport infrastructure that links
waterborne shipping with highways, railways, and urban roads [Figure 1]. Due to the area's distinctive
industrial profile, a high concentration of warehousing and logistics enterprises has developed, resulting in
frequent freight vehicle activity. Consequently, traffic-related air pollution in this district is notably severe.

Simulation of traffic-derived NO pollution using the CALPUFF model
x
The CALPUFF modeling system consists of four main components: a preprocessing module, a
meteorological module (CALMET), a dispersion module (CALPUFF), and a postprocessing module
(CALPOST) [Figure 2]. First, the preprocessing module converts land use and terrain elevation data into
georeferenced formats compatible with the CALMET module. It also processes surface and upper-air