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| Titel |
Compact, Low-power Nitrous Oxide Monitor for Eddy Flux Soil Emission Measurements |
| VerfasserIn |
Joanne Shorter, David Nelson, Barry McManus, Mark Zahniser |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250107664
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| Publikation (Nr.) |
 EGU/EGU2015-7374.pdf |
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| Zusammenfassung |
| Nitrous oxide, N2O, is one of the most important greenhouse and ozone-depleting gases. The
concentration of N2O in the atmosphere has been increasing at a rate of 0.3% per year, with
this rise believed to be largely due to soil emissions and agricultural practices (Park et al.
2011; Park et al. 2012). The eddy covariance technique, which requires fast (~10 Hz)
measurement of mixing ratios and wind data, is perhaps the most effective technique
available to quantify the exchange of gases between the atmosphere and the biosphere. It is
very useful for addressing the high spatial and temporal variability of nitrous oxide emissions
from soils.
Nitrous oxide monitors appropriate for eddy covariance measurements generally require
large flow rates (~10 - 15 slpm) and high speed, high power vacuum pumps (500 lpm, 600
W). These requirements complicate and in some environments prevent successful field
deployment. We have addressed this by developing a compact, low-power nitrous
oxide monitor for eddy flux or soil chamber measurements with a dramatically
reduced sample cell volume. The sample volume is reduced nearly 5 fold (from
500 to 108 cm3) with only a two-fold reduction in optical path length (from 76
m to 36 m). The new multi-pass cell has an aluminum tube insert with a tapered
internal volume that follows the mode envelope of the multi-pass spot pattern. This
permits the use of a much smaller, lower power pump while still achieving high
precision and fast response. Precision of 26 parts per trillion (ppt) in 1 sec was
achieved with a 1/e response time of 0.14 s using a relatively low speed vacuum pump
(100 lpm, 350 W). Further reductions in cell volume are planned which should
permit sensitive eddy covariance measurements of nitrous oxide using an even
smaller, lower power pump (60 lpm, 160 W) and modest sample flow rates (~2
slpm).
We have also recently studied the application of a standard ARI nitrous oxide monitor
to measurement of N2O isotopologues emitted into soil chambers. We measured
nitrous oxide isotopologues, 14N15N16O (456), 14N14N16O (446), and15N14N16O
(546), in the headspace of soil incubation jars. No significant interferences were
observed and differences in isotopic ratios between distinctive soil samples were
observed.
Park, S., P. Croteau, K. A. Boering, D. M. Etheridge, D. Ferretti, P. J. Fraser, K. R. Kim,
P. B. Krummel, R. L. Langenfelds, T. D. van Ommen, L. P. Steele and C. M. Trudinger
(2012). "Trends and seasonal cycles in the isotopic composition of nitrous oxide since 1940."
Nature Geosci 5(4): 261-265.
Park, S., T. Pérez, K. Boering, S. Trumbore, J. Gil, S. Marquina and S. Tyler (2011). "Can
N2O stable isotopes and isotopomers be useful tools to characterize sources and microbial
pathways of N2O production and consumption in tropical soils?" Global Biogeochemical
Cycles 25(1): GB1001. |
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