Index Geophysics

Vehicle emissions of greenhouse gases and related tracers from a tunnel study: CO : CO2, N2O : CO2, CH4 : CO2, O2 : CO2 ratios, and the stable isotopes 13C and 18O in CO2 and CO

Measurements of CO₂, CO, N₂O and CH₄ mole fractions, O₂ / N₂ ratios and the stable isotopes ¹³C and ¹⁸O in CO₂ and CO have been performed in air samples from the Islisberg highway tunnel (Switzerland). The molar CO : CO₂ ratios, with an average of (4.15 ± 0.34) ppb:ppm, are lower than reported in previous studies, pointing to a reduction in CO emissions from traffic. The ¹³C in CO₂ reflects the isotopic composition of the fuel. ¹⁸O in CO₂ is slightly depleted compared to the ¹⁸O in atmospheric O₂, and shows significant variability. In contrast, the δ¹³C values of CO show that significant fractionation takes place during CO destruction in the catalytic converter. ¹³C in CO is enriched by 3‰ compared to the ¹³C in the fuel burnt, while the ¹⁸O content is similar to that of atmospheric O₂. We compute a fractionation constant of (−2.7 ± 0.7)‰ for ¹³C during CO destruction. The N₂O : CO₂ average ratio of (1.8 ± 0.2) × 10⁻² ppb:ppm is significantly lower than in past studies, showing a reduction in N₂O emissions likely related to improvements in the catalytic converter technology. We also observed small CH₄ emissions, with an average CH₄ : CO₂ ratio of (4.6 ± 0.2) × 10^−2 ppb:ppm. The O₂ : CO₂ ratios of (−1.47 ± 0.01) ppm:ppm are very close to the expected, theoretically calculated values of O₂ depletion per CO₂ enhancement.

Popa, M. E.

Vollmer, M. K.

Jordan, A.

Brand, W. A.

Pathirana, S. L.

Rothe, M.

Röckmann, T.

2018-01-15

Text

application/pdf

10.5194/acp-14-2105-2014

https://acp.copernicus.org/articles/14/2105/2014/

eISSN: 1680-7324

eng