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Page 2 of 19 Wang et al. Carbon Footprints 2024;3:14 https://dx.doi.org/10.20517/cf.2024.19

INTRODUCTION
Global carbon dioxide (CO ) emissions have been rising at an alarming rate, driven primarily by fossil fuel
2
consumption, industrial activities, and deforestation. These emissions contributed to global warming and
resulting climate change, which posed a severe threat to ecosystems, economies, and human health
[1]
worldwide . Despite international society’s efforts to curb CO emissions, including agreements such as the
2
Paris Agreement , global emissions continued to increase, with significant contributions from both
[2]
developed and developing nations, emphasizing the need for immediate and sustained reductions in global
[3,4]
CO emissions to mitigate the worst impacts of climate change . In response, many countries were
2
implementing ambitious policies and initiatives, such as transitioning to renewable energy sources,
[5]
enhancing energy efficiency, promoting electric vehicles , and investing in carbon capture and storage
technologies . These measures are critical to meeting global climate targets and slowing the pace of climate
[6]
change.
In this global context, China pledged in 2020 to strive for carbon peaking by 2030 and achieve carbon
neutrality by 2060 in response to the escalating global warming crisis and the imperative to mitigate CO
2
emissions . This commitment reflects China's active engagement in addressing climate change and
[7,8]
underscores its dedication to sustainable development and environmental protection. As the world’s largest
CO emitter, driven by rapid urbanization and industrialization, China recognizes the critical importance of
2
developing city-specific emission reduction policies . In alignment with this goal, the Ministry of Ecology
[9]
and Environment of the People’s Republic of China launched the “Pilot Project for Carbon Monitoring and
Assessment” in September 2021. This project aimed to implement pilot projects focusing on carbon
monitoring and assessment in target cities and key industries to enhance the collaborative monitoring
capability of pollution and carbon reduction. Chengdu, one of the 16 pilot cities, would concentrate on
high-resolution and high-precision CO monitoring and assessment, establishing a comprehensive CO
2
2
concentration monitoring network.

Recognizing the central role of cities in achieving these ambitious goals, China’s carbon emission mitigation
initiatives have focused on city areas, which were crucial participants in the realization of CO emissions
2
control objectives [10-12] . As primary hubs for human activities, cities concentrate substantial population,
exhibit high economic density, and display elevated energy consumption intensity, thereby emerging as a
significant source of anthropogenic CO emissions . From a global perspective, according to statistical
[13]
2
analyses, Wei et al. (2021) stated that among the 167 cities or metropolitan areas across 53 countries, the top
25 cities alone contributed to more than half of the global emissions . Another survey from the
[14]
International Energy Agency (IEA) estimated that city areas accounted for 71% of global energy
consumption CO emissions . In China, where rapid urbanization continued to drive population
[15]
2
migration to cities, 40% of city residents consumed 75% of the total energy , leading to city environmental
[16]
degradation, particularly in the thermal environment, due to increased fuel usage, material consumption,
housing demand, and uncontrolled land use expansion [17-20] . Owing to their substantial energy consumption
driven by construction, production, and economic growth, cities have become critical arenas for
implementing emission-reduction strategies and are central to the global search for climate change
mitigation solutions [21-24] .

To establish city-scale carbon monitoring networks that can effectively guide regional CO emission
2
reduction, CO emission flux inversion is essential. This inversion process not only helps identify specific
2
emission sources but also provides key data for policymakers to implement effective emission reduction