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| Titel |
Pseudo steady states of HONO measured in the nocturnal marine boundary layer: a conceptual model for HONO formation on aqueous surfaces |
| VerfasserIn |
P. Wojtal, J. D. Halla, R. McLaren |
| 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 ; 11, no. 7 ; Nr. 11, no. 7 (2011-04-05), S.3243-3261 |
| Datensatznummer |
250009590
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| Publikation (Nr.) |
 copernicus.org/acp-11-3243-2011.pdf |
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| Zusammenfassung |
| A complete understanding of the formation mechanism of nitrous acid
(HONO) in the ambient atmosphere is complicated by a lack of
understanding of processes occurring when aqueous water is present. We
report nocturnal measurements of HONO, SO2 and NO2
by differential optical absorption spectroscopy over the ocean surface
in a polluted marine environment. In this aqueous environment, we
observed reproducible pseudo steady states (PSS) of HONO every night,
that are fully formed shortly after sunset, much faster than seen in
urban environments. During the PSS period, HONO is constant with time,
independent of air mass source and independent of the concentration of
NO2. The independence of HONO on the concentration of
NO2 implies a 0° order formation process, likely on
a saturated surface, with reversible partitioning of HONO to the gas
phase, through vaporization and deposition to the surface. We observed
median HONO/NO2 ratios starting at 0.13 at the beginning of
the PSS period (with an apparent lower bound of 0.03), rising to
median levels of ~0.30 at the end of the PSS period (with an
upper bound >1.0). The implication of these numbers is that they
suggest a common surface mechanism of HONO formation on terrestrial and aqueous
surfaces, with an increase in the HONO/NO2 ratio with the
amount of water available at the surface. The levels of HONO during
the nocturnal PSS period are positively correlated with temperature,
consistent with a partitioning of HONO from the surface to the gas
phase with an apparent enthalpy of vaporization of ΔHSNL (HONO)=55.5±5.4 kJ mol−1. The
formation mechanism on aqueous surfaces is independent of relative
humidity (RH), despite observation of a negative HONO-RH
correlation. A conceptual model for HONO formation on ambient aqueous
surfaces is presented, with the main elements being the presence of
a surface nanolayer (SNL), highly acidic and saturated with N(IV)
precursors, production of HNO3, that diffuses to underlying water
layers, and HONO, which partitions reversibly between the SNL and the
gas phase. Implications of the conceptual model are discussed. |
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