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| Titel |
Using semi-continuous, in-situ measurements of nitrous oxide isotopic composition at a suburban site to track emission processes |
| VerfasserIn |
Eliza Harris, Stephan Henne, Christoph Hüglin, Christoph Zellweger, Béla Tuzson, Erkan Ibraim, Lukas Emmenegger, Joachim Mohn |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250137340
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| Publikation (Nr.) |
 EGU/EGU2017-12.pdf |
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| Zusammenfassung |
| Nitrous oxide (N2O) is a potent greenhouse gas and the strongest ozone-destroying substance
emitted this century. The atmospheric N2O mole fraction has been increasing at a rate of
0.2-0.3% per year over the past decades due to anthropogenic emissions; in addition, recent
results suggest that the rate of increase is rising – therefore effective mitigation of N2O
emissions is a critical point for environmental policy. However, N2O sources are
poorly defined and disperse, complicating the development of targeted mitigation
strategies.
Online isotopic measurements using preconcentration and laser spectroscopy [1,2,3] have
great potential to unravel spatial and temporal variations in sources, sinks and chemistry of
trace gases such as N2O. Semi-continuous, real-time measurements of N2O isotopic
composition (δ18O, site preference [SP = 14N15N16O - 15N14N16O] and δ15Nbulk)
were performed at the suburban site of Dübendorf, Switzerland, for 19 months
between July 2014 and February 2016. The data precision reached 0.1‰ in the final
months, thus the results could clearly identify nocturnal build-up of N2O, with a
corresponding decrease in δ18O, SP and δ15Nbulk due to isotopically depleted anthropogenic
sources.
Daily mean source isotopic composition was calculated by considering the measured and
the background mole fraction and isotopic composition. Delta values of the mean emission
source were highest in winter, with a seasonal cycle of 12, 8 and 5‰ for δ18O, SP and
δ15Nbulk respectively. The chemical and meteorological parameters controlling source
isotopic composition were considered using data from the Swiss National Air Pollution
Monitoring Network (NABEL) as well as a transport regime cluster analysis. A clear spatial
distribution for source isotopic composition was observed for δ18O, as well as a significant
relationship with the level of urban pollution, indicating δ18O may be a strong indicator of
combustion/industrial vs. agricultural N2O. In contrast, δ15Nbulk and particularly SP appear
to vary too strongly in response to other factors affecting emission processes to
provide a useful distinction between source categories on a regional scale – these
isotopocules may however be useful to distinguish emission pathways on a local
scale.
For comparison, FLEXPART-COSMO transport simulations [4] were combined with
emissions from the EDGAR inventory and estimates of source isotopic composition from
literature, to simulate N2O isotopic composition at the sampling site. The model was able to
capture variability in N2O mole fraction adequately (R2 = 0.34; p <<0.01). However, the
measured variability in source isotopic composition was 1-2 orders of magnitude larger than
simulated, illustrating that our knowledge of isotopic source signatures – in particular
technical N2O sources – is still too limited to successfully model variations in ambient N2O
isotopic composition.
[1] Mohn et al. (2012) Atmospheric Measurement Techniques, doi:10.5194/amt-5-1601-2012
[2] Harris et al. (2014) Analytical Chemistry, doi: 10.1021/ac403606u.
[3] Röckmann et al. (2016) Atmospheric Chemistry and Physics, doi:10.5194/acp-16-10469-2016.
[4] Henne et al. (2016) Atmospheric Chemistry and Physics, doi:10.5194/acp-16-3683-2016. |
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