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Titel |
Atmospheric HULIS: How humic-like are they? A comprehensive and critical review |
VerfasserIn |
E. R. Graber, Y. Rudich |
Medientyp |
Artikel
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Sprache |
Englisch
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ISSN |
1680-7316
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Digitales Dokument |
URL |
Erschienen |
In: Atmospheric Chemistry and Physics ; 6, no. 3 ; Nr. 6, no. 3 (2006-03-06), S.729-753 |
Datensatznummer |
250003519
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Publikation (Nr.) |
copernicus.org/acp-6-729-2006.pdf |
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Zusammenfassung |
A class of organic molecules extracted from atmospheric aerosol particles
and isolated from fog and cloud water has been termed HUmic-LIke Substances
(HULIS) due to a certain resemblance to terrestrial and aquatic humic and
fulvic acids. In light of the interest that this class of atmospheric
compounds currently attracts, we comprehensively review HULIS properties, as
well as laboratory and field investigations concerning their formation and
characterization in atmospheric samples. While sharing some important
features such as polyacidic nature, accumulating evidence suggests that
atmospheric HULIS differ substantially from terrestrial and aquatic humic
substances. Major differences between HULIS and humic substances, including
smaller average molecular weight, lower aromatic moiety content, greater
surface activity, better droplet activation ability, as well as others, are
highlighted. Several alternatives are proposed that may explain such
differences: (1) the possibility that mono- and di-carboxylic acids and
mineral acids abundant in the atmosphere prevent the formation of large
humic "supramolecular associations"; (2) that large humic macromolecules
are destroyed in the atmosphere by UV radiation, O3, and OH- radicals; (3) that "HULIS" actually consists of a complex, unresolved
mixture of relatively small molecules rather than macromolecular entities;
and (4) that HULIS formed via abiotic and short-lived oxidative reaction
pathways differ substantially from humic substances formed over long time
periods via biologically-mediated reactions. It should also be recalled that
the vast majority of studies of HULIS relate to the water soluble fraction,
which would include only the fulvic acid fraction of humic substances, and
exclude the humic acid (base-soluble) and humin (insoluble) fractions of
humic substances. A significant effort towards adopting standard extraction
and characterization methods is required to develop a better and meaningful
comparison between different HULIS samples. |
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