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| Titel |
Renewed methane increase (2007–2014): contribution of oil and natural gas emissions determined from methane and ethane column observations |
| VerfasserIn |
Petra Hausmann, Ralf Sussmann, Dan Smale |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133789
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| Publikation (Nr.) |
 EGU/EGU2016-14439.pdf |
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| Zusammenfassung |
| Harmonized time series of column-averaged mole fractions of atmospheric methane and
ethane over the period 1999–2014 are derived from solar Fourier transform infrared (FTIR)
measurements at the Zugspitze summit (47˚ N, 2964 m a.s.l.) and at Lauder (45˚
S, 370 m a.s.l.). Long-term trend analysis reveals a consistent renewed methane
increase since 2007 of 6.2 [5.6, 6.9] ppb yr−1 at the Zugspitze and 6.0 [5.3, 6.7]
ppb yr−1 at Lauder (95 % confidence intervals). Several recent studies provide
pieces of evidence that the renewed methane increase is most likely driven by two
main factors: (i) increased methane emissions from tropical wetlands, followed by
(ii) increased thermogenic methane emissions due to growing oil and natural gas
production. Here, we quantify the magnitude of the second class of sources, using
long-term measurements of atmospheric ethane as tracer for thermogenic methane
emissions. In 2007, after years of weak decline, the Zugspitze ethane time series shows
the sudden onset of a significant positive trend (2.3 [1.8, 2.8] × 10−2 ppb yr−1
for 2007–2014), while a negative trend persists at Lauder after 2007 (-0.4 [-0.6,
-0.1] × 10−2 ppb yr−1). Zugspitze methane and ethane time series are significantly
correlated for the period 2007–2014 and can be assigned to thermogenic methane
emissions with an ethane-to-methane ratio of 10–21 %. We present optimized emission
scenarios for 2007–2014 derived from an atmospheric two-box model. From our trend
observations we infer a total ethane emission increase over the period 2007–2014
from oil and natural gas sources of 1–11 Tg yr−1 along with an overall methane
emission increase of 24–45 Tg yr−1. Based on these results, the oil and natural gas
emission contribution C to the renewed methane increase is deduced using three
different emission scenarios with dedicated ranges of methane-to-ethane ratios
(MER). Reference scenario 1 assumes an oil and gas emission combination with
MER = 3.3–7.6, which results in a minimum contribution C > 28 % (given as
lower bound of 99 % confidence interval). For the limiting cases of pure oil-related
emissions with MER = 1.7–3.3 (scenario 2) and pure natural gas sources with MER =
7.6–12.1 (scenario 3) the results are C > 13 % and C > 53 %, respectively. Our
results suggest that long-term observations of column-averaged ethane provide
a valuable constraint on the source attribution of methane emission changes and
provide basic knowledge for developing effective climate change mitigation strategies. |
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