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| Titel |
Quantifying the isotopic composition of NOx emission sources: An analysis of collection methods |
| VerfasserIn |
D. Fibiger, M. Hastings |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068415
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| Zusammenfassung |
| We analyze various collection methods for nitrogen oxides, NOx (NO2 and NO), used to
evaluate the nitrogen isotopic composition (δ15N). Atmospheric NOx is a major contributor
to acid rain deposition upon its conversion to nitric acid; it also plays a significant role in
determining air quality through the production of tropospheric ozone. NOx is released by
both anthropogenic (fossil fuel combustion, biomass burning, aircraft emissions) and natural
(lightning, biogenic production in soils) sources. Global concentrations of NOx are rising
because of increased anthropogenic emissions, while natural source emissions also
contribute significantly to the global NOx burden. The contributions of both natural and
anthropogenic sources and their considerable variability in space and time make it
difficult to attribute local NOx concentrations (and, thus, nitric acid) to a particular
source. Several recent studies suggest that variability in the isotopic composition
of nitric acid deposition is related to variability in the isotopic signatures of NOx
emission sources. Nevertheless, the isotopic composition of most NOx sources has
not been thoroughly constrained. Ultimately, the direct capture and quantification
of the nitrogen isotopic signatures of NOx sources will allow for the tracing of
NOx emissions sources and their impact on environmental quality. Moreover, this
will provide a new means by which to verify emissions estimates and atmospheric
models.
We present laboratory results of methods used for capturing NOx from air into solution.
A variety of methods have been used in field studies, but no independent laboratory
verification of the efficiencies of these methods has been performed. When analyzing isotopic
composition, it is important that NOx be collected quantitatively or the possibility of
fractionation must be constrained. We have found that collection efficiency can vary widely
under different conditions in the laboratory and fractionation does not vary predictably with
collection efficiency. For example, prior measurements frequently utilized triethanolamine
solution for collecting NOx, but the collection efficiency was found to drop quickly as
the solution aged. The most promising method tested is a NaOH/KMnO4 solution
(Margeson and Knoll, Anal. Chem., 1985) which can collect NOx quantitatively from
the air. Laboratory tests of previously used methods, along with progress toward
creating a suitable and verifiable field deployable collection method will be presented. |
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