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Volume 16
Issue 12
10.3390/atmos16121351
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This is an early access version, the complete PDF, HTML, and XML versions will be available soon.
Article

Mobile Measurement of CO2 and CH4 on Ring Roads and Expressways in Xi’an, China: Spatial Patterns and Influencing Factors

by
Feng Wei
1,
Ji Zhou
1,
Yingfei Cao
1,
Xuan Zhang
1,
Qian Li
1,
Nixia Cui
1,
Yang Zhuo
2,
Jie Tian
3,
Jiarui Wu
3,
Shugang Wu
3,
Zhenpeng Ma
4,
Changlin Zhan
5,
Weiwei Chen
6,
Haiyan Ni
2,* and
Chong Wei
4,6,7,*
1
Shaanxi Transportation Holding Green Development Group Co., Ltd., Xi’an 710018, China
2
School of Environmental and Municipal Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, China
3
State Key Laboratory of Loess Science, Institute of Earth Environment, Chinese Academy of Sciences, Xi’an 710061, China
4
Shaanxi Key Laboratory of Carbon Dioxide Sequestration and Enhanced Oil Recovery, Research Institute of Yanchang Petroleum Co., Ltd., Xi’an 710065, China
5
School of Environmental Science and Engineering, Hubei Key Laboratory of Mine Environmental Pollution Control and Remediation, Hubei Polytechnic University, Huangshi 435003, China
6
Key Laboratory of Groundwater Resources and Environment of the Ministry of Education, College of New Energy and Environment, Jilin University, Changchun 130021, China
7
Center for Advanced Energy System & Equipment, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210, China
*
Authors to whom correspondence should be addressed.
Atmosphere 2025, 16(12), 1351; https://doi.org/10.3390/atmos16121351 (registering DOI)
Submission received: 26 October 2025 / Revised: 22 November 2025 / Accepted: 27 November 2025 / Published: 28 November 2025
(This article belongs to the Special Issue Sources, Spatio-Temporal Distribution and Health Effects of Atmospheric Compositions (2nd Edition))
Versions Notes

Abstract

Carbon dioxide (CO2) and methane (CH4) are important greenhouse gases emitted by vehicles, yet their spatial pattern within urban road networks remains poorly characterized. This study conducts mobile measurements of CO2 and CH4 along the 1st Ring Road (mean speed of the monitoring vehicle: 22 km h−1), 2nd Ring Road (22 km h−1), and Ring Expressway (90 km h−1) in Xi’an, China, to investigate their spatial distribution and influencing factors. Average CO2 and CH4 concentrations on the three ring roads exhibited a clear decline with increasing distance from the city center. Both CO2 and CH4 showed higher concentrations at lower vehicle speeds and at higher traffic volumes, but CH4 hotspots differed spatially from CO2 and exhibited weaker dependence on vehicle speed, indicating additional off-road CH4 sources (e.g., natural gas leaks, nearby livestock farms). In a tunnel case study, CO2, CH4, and CO concentrations increased concurrently from entrance to exit, resulting in strong correlations between CH4 and CO2 (R2 = 0.86) and between CO and CO2 (R2 = 0.66). This produced emission ratios (ΔCH4/ΔCO2 = 0.160 ppb ppm−1; ΔCO/ΔCO2 = 3.151 ppb ppm−1), representative of incomplete combustion under congestion. Our results provide direct observational evidence linking urban traffic dynamics to greenhouse gas emissions and emphasize the need for congestion mitigation to reduce on-road climate-relevant emissions.
Keywords: greenhouse gases; mobile on-road measurements; road tunnel; spatial distribution; vehicular emissions; emission ratios; cavity ring-down spectrometer greenhouse gases; mobile on-road measurements; road tunnel; spatial distribution; vehicular emissions; emission ratios; cavity ring-down spectrometer

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MDPI and ACS Style

Wei, F.; Zhou, J.; Cao, Y.; Zhang, X.; Li, Q.; Cui, N.; Zhuo, Y.; Tian, J.; Wu, J.; Wu, S.; et al. Mobile Measurement of CO2 and CH4 on Ring Roads and Expressways in Xi’an, China: Spatial Patterns and Influencing Factors. Atmosphere 2025, 16, 1351. https://doi.org/10.3390/atmos16121351

AMA Style

Wei F, Zhou J, Cao Y, Zhang X, Li Q, Cui N, Zhuo Y, Tian J, Wu J, Wu S, et al. Mobile Measurement of CO2 and CH4 on Ring Roads and Expressways in Xi’an, China: Spatial Patterns and Influencing Factors. Atmosphere. 2025; 16(12):1351. https://doi.org/10.3390/atmos16121351

Chicago/Turabian Style

Wei, Feng, Ji Zhou, Yingfei Cao, Xuan Zhang, Qian Li, Nixia Cui, Yang Zhuo, Jie Tian, Jiarui Wu, Shugang Wu, and et al. 2025. "Mobile Measurement of CO2 and CH4 on Ring Roads and Expressways in Xi’an, China: Spatial Patterns and Influencing Factors" Atmosphere 16, no. 12: 1351. https://doi.org/10.3390/atmos16121351

APA Style

Wei, F., Zhou, J., Cao, Y., Zhang, X., Li, Q., Cui, N., Zhuo, Y., Tian, J., Wu, J., Wu, S., Ma, Z., Zhan, C., Chen, W., Ni, H., & Wei, C. (2025). Mobile Measurement of CO2 and CH4 on Ring Roads and Expressways in Xi’an, China: Spatial Patterns and Influencing Factors. Atmosphere, 16(12), 1351. https://doi.org/10.3390/atmos16121351

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