Refinement of vehicle emission factor estimation in tunnel experiments using CFD and field measurement

Xiaoyu Liang ¹, Jianfei Peng ¹, Yan Liu ¹

⁰Tianjin Key Laboratory of Urban Transport Emission Research & State Environmental Protection Key Laboratory of Urban Ambient Air Particulate Matter Pollution Prevention and Control, College of Environmental Science and Engineering, Nankai University, Tianjin, 300071, China.

Environmental Pollution (Barking, Essex : 1987) +

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July 17, 2025

View abstract on PubMed

Summary

Tunnel experiments can underestimate vehicle emission factors by up to 40%. This study uses CFD modeling to correct these errors, improving accuracy for emission inventories and air quality management.

Area Of Science

Environmental Science
Atmospheric Chemistry
Transportation Engineering

Background

Tunnel experiments are standard for vehicle emission factor (EF) determination.
Spatial heterogeneity in wind and pollutant dispersion causes inaccuracies in field measurements.
Limited sampling locations can lead to significant underestimation of real-world emissions.

Purpose Of The Study

To integrate Computational Fluid Dynamics (CFD) modeling with tunnel measurements.
To quantify and correct errors in fleet-average vehicle emission factors derived from tunnel studies.
To enhance the reliability of tunnel-derived EFs for accurate emission inventories.

Main Methods

Combined CFD simulations with real-world tunnel measurements.
Developed and validated correction schemes for emission factors.
Analyzed the influence of external atmospheric conditions on internal tunnel flows.

Main Results

Field measurements alone underestimated EFs by up to 40%, especially under low traffic and weak wind.
Average EFs for NOx, CO, and PM2.5 were underestimated by 24.50, 161.66, and 3.33 mg km⁻¹·veh⁻¹, respectively.
CFD analysis revealed external atmospheric conditions significantly impact tunnel flows near entrances.

Conclusions

The study provides a validated method to correct tunnel-derived emission factors, enhancing accuracy.
Corrected EFs improve emission inventories and support targeted air quality management policies.
Findings offer guidance for optimizing tunnel siting and sampling strategies for future studies.

Keywords:

Pollutant dispersion Traffic emission Tunnel measurement Vehicle emission factor