Nitrous oxide (N₂O) isotopic composition in the troposphere : instrumentation, observations at Mace Head, Ireland, and regional modeling
Author(s)Potter, Katherine Ellison
Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.
Ronald G. Prinn and Shuhei Ono.
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Nitrous oxide (N₂O) is a significant greenhouse gas and main contributor to stratospheric ozone destruction. Surface measurements of N₂O mole fractions have been used to attribute source and sink strengths, but large uncertainties remain. Stable isotopic ratios of N₂O (here considered ¹⁴N¹⁵N¹⁶O, ¹⁵N¹⁴N¹⁶O, ¹⁴N¹⁴N¹⁸O, relative to the abundant ¹⁴N¹⁴N¹⁶O) linked to source and sink isotopic signatures can provide additional constraints on emissions and counter-balancing stratospheric sink. However, the isotopic composition in the troposphere has been regarded and measured as a fixed value, limited by insufficient measurement precision and few data. This thesis provides the foundation for high-frequency, high-precision measurements and utilization of N₂O tropospheric isotopic composition. This is achieved through the development of a new measuring capability with sufficient precision to detect the subtle signals of N₂O isotopic composition in tropospheric air and uniquely fully-automated and high-frequency capable. This instrument was applied to produce the first set of tropospheric air observations gathered at a remote research station covering a full annual cycle, paired with air origin information, and providing a valuable assessment of tropospheric composition and its potential utility. The first regional model of tropospheric N₂O isotopic composition was developed for further assessment of expected variability and utility of isotopic composition data. The optimized fully-automated, liquid-cryogen-free pre-concentration device coupled to continuous flow IRMS resulted in ¹⁵N site-specific precisions markedly improved over other systems of 0.11 and 0.14 0/00 (1[sigma]) for [delta]¹⁵N[alpha] and [delta]¹⁵Nbulk, respectively, and among the best bulk composition precisions of 0.05 and 0.10 0/00 for [delta]¹⁵Nbulk and [delta]¹⁸O, respectively. The high-precision, non-continuous flask observations of N₂O ¹⁵N site-specific composition (January 2010 to January 2011; Mace Head Atmospheric Research Station, Ireland) detected statistically significant signals on short-term and annual timescales, and when analyzed with air history information showed consistencies with source-receptor relationships. No seasonal cycle could be detected in the low-frequency observations, but regional model scenarios of the stratospheric seasonal signal resulted in amplitudes at the cusp of current measurement capabilities. This thesis illustrated detectable variations in tropospheric N₂O isotopic composition which can potentially reduce uncertainty in the N₂O budget with high-frequency, high-precision observations, now feasible by the instrumentation developed here.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references.
DepartmentMassachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.
Massachusetts Institute of Technology
Earth, Atmospheric, and Planetary Sciences.