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| Titel |
Vertical profiles of O3 and NOx chemistry in the polluted nocturnal boundary layer in Phoenix, AZ: I. Field observations by long-path DOAS |
| VerfasserIn |
S. Wang, R. Ackermann, J. Stutz |
| 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. 9 ; Nr. 6, no. 9 (2006-07-06), S.2671-2693 |
| Datensatznummer |
250003983
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| Publikation (Nr.) |
 copernicus.org/acp-6-2671-2006.pdf |
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| Zusammenfassung |
| Nocturnal chemistry in the atmospheric boundary layer plays a key role in
determining the initial chemical conditions for photochemistry during the
following morning as well as influencing the budgets of O3 and
NO2. Despite its importance, chemistry in the nocturnal boundary layer
(NBL), especially in heavily polluted urban areas, has received little
attention so far, which greatly limits the current understanding of the
processes involved. In particular, the influence of vertical mixing on
chemical processes gives rise to complex vertical profiles of various
reactive trace gases and makes nocturnal chemistry altitude-dependent. The
processing of pollutants is thus driven by a complicated, and not well
quantified, interplay between chemistry and vertical mixing.
In order to gain a better understanding of the altitude-dependent
nocturnal chemistry in the polluted urban environment, a field study
was carried out in the downtown area of Phoenix, AZ, in summer 2001.
Vertical profiles of reactive species, such as O3, NO2,
and NO3, were observed in the lowest 140 m of the troposphere
throughout the night. The disappearance of these trace gas vertical
gradients during the morning coincided with the morning transition
from a stable NBL to a well-mixed convective layer. The vertical
gradients of trace gas levels were found to be dependent on both
surface NOx emission strength and the vertical stability of
the NBL. The vertical gradients of Ox, the sum of O3
and NO2, were found to be much smaller than those of O3
and NO2, revealing the dominant role of NO emissions followed
by the O3+NO reaction for the altitude-dependence of nocturnal
chemistry in urban areas. Dry deposition, direct emissions, and
other chemical production pathways of NO2 also play a role for
the Ox distribution. Strong positive vertical gradients of
NO3, that are predominantly determined by NO3 loss near
the ground, were observed. The vertical profiles of NO3 and the
calculated vertical profiles of its reservoir species
(N2O5) confirm earlier model results suggesting complex
vertical distributions of atmospheric denoxification processes
during the night. |
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