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| Titel |
HONO fluxes from soil surfaces: an overview |
| VerfasserIn |
Dianming Wu, Matthias Sörgel, Alexandra Tamm, Nina Ruckteschler, Emilio Rodriguez-Caballero, Yafang Cheng, Ulrich Pöschl, Bettina Weber |
| 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 |
250126389
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| Publikation (Nr.) |
 EGU/EGU2016-6100.pdf |
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| Zusammenfassung |
| Gaseous nitrous acid (HONO) contributes up to 80% of atmospheric hydroxyl (OH) radicals
and is also linked to health risks through reactions with tobacco smoke forming carcinogens.
Field and modeling results suggested a large unknown HONO source in the troposphere
during daytime. By measuring near ground HONO mixing ratio, up to 30% of HONO can be
released from forest, rural and urban ground as well as snow surfaces. This source has been
proposed to heterogeneous reactions of nitrogen dioxide (NO2) on humic acid surfaces or
nitric acid photolysis. Laboratory studies showed that HONO emissions from bulk soil
samples can reach 258 ng m−2 s−1 (in term of nitrogen), which corresponding
to 1.1 × 1012 molecules cm−2 s−1and ∼ 100 times higher than most of the field
studies, as measured by a dynamic chamber system. The potential mechanisms
for soil HONO emissions include chemical equilibrium of acid-base reaction and
gas-liquid partitioning between soil nitrite and HONO, but the positive correlation
of HONO fluxes with pH (largest at neutral and slightly alkaline) points to the
dominance of the formation process by ammonia-oxidizing bacteria (AOB). In general
soil surface acidity, nitrite concentration and abundance of ammonia-oxidizing
bacteria mainly regulate the HONO release from soil. A recent study showed that
biological soil crusts in drylands can also emit large quantities of HONO and NO,
corresponding to ∼20% of global nitrogen oxide emissions from soils under natural
vegetation. Due to large concentrations of microorganisms in biological soil crusts,
particularly high HONO and NO emissions were measured after wetting events.
Considering large areas of arid and arable lands as well as peatlands, up to 70% of global
soils are able to emitting HONO. However, the discrepancy between large soil
HONO emissions measured in lab and low contributions of HONO flux from ground
surfaces in field as well as the role of microorganisms should be further investigated. |
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