Vehicle emissions of greenhouse gases and related tracers from a tunnel study: CO : CO<sub>2</sub>, N<sub>2</sub>O : CO<sub>2</sub>, CH<sub>4</sub> : CO<sub>2</sub>, O<sub>2</sub> : CO<sub>2</sub> ratios, and the stable isotopes <sup>13</sup>C and <sup>18</sup>O in CO<sub>2</sub> and CO
Measurements of CO<sub>2</sub>, CO, N<sub>2</sub>O and CH<sub>4</sub> mole fractions, O<sub>2</sub> / N<sub>2</sub> ratios and the stable isotopes <sup>13</sup>C and <sup>18</sup>O in CO<sub>2</sub> and C...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/14/2105/2014/acp-14-2105-2014.pdf |
| Summary: | Measurements of CO<sub>2</sub>, CO, N<sub>2</sub>O and CH<sub>4</sub> mole fractions,
O<sub>2</sub> / N<sub>2</sub> ratios and the stable isotopes <sup>13</sup>C and <sup>18</sup>O in
CO<sub>2</sub> and CO have been performed in air samples from the Islisberg
highway tunnel (Switzerland). The molar CO : CO<sub>2</sub> 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 <sup>13</sup>C in
CO<sub>2</sub> reflects the isotopic composition of the fuel. <sup>18</sup>O in CO<sub>2</sub>
is slightly depleted compared to the <sup>18</sup>O in atmospheric O<sub>2</sub>, and
shows significant variability. In contrast, the δ<sup>13</sup>C values of
CO show that significant fractionation takes place during CO destruction in
the catalytic converter. <sup>13</sup>C in CO is enriched by 3‰ compared to the <sup>13</sup>C in the fuel burnt, while the
<sup>18</sup>O content is similar to that of atmospheric O<sub>2</sub>. We compute a
fractionation constant of (−2.7 ± 0.7)‰ for
<sup>13</sup>C during CO destruction. The N<sub>2</sub>O : CO<sub>2</sub> average ratio of (1.8 ± 0.2) × 10<sup>−2</sup> ppb:ppm is significantly lower than in
past studies, showing a reduction in N<sub>2</sub>O emissions likely related to
improvements in the catalytic converter technology. We also observed small
CH<sub>4</sub> emissions, with an average CH<sub>4</sub> : CO<sub>2</sub> ratio of (4.6 ± 0.2) × 10<sup>−2</sup> ppb:ppm.
The O<sub>2</sub> : CO<sub>2</sub> ratios of (−1.47 ± 0.01) ppm:ppm are very close to the expected, theoretically
calculated values of O<sub>2</sub> depletion per CO<sub>2</sub> enhancement. |
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| ISSN: | 1680-7316 1680-7324 |