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| Titel |
Observations of the diurnal and seasonal trends in nitrogen oxides in the western Sierra Nevada |
| VerfasserIn |
J. G. Murphy, D. A. Day, P. A. Cleary, P. J. Wooldridge, R. C. Cohen |
| 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. 12 ; Nr. 6, no. 12 (2006-11-27), S.5321-5338 |
| Datensatznummer |
250004188
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| Publikation (Nr.) |
 copernicus.org/acp-6-5321-2006.pdf |
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| Zusammenfassung |
Observations of speciated nitrogen oxides, namely NO2, total peroxy
nitrates (ΣPNs), total alkyl nitrates (ΣANs), and HNO3
by thermal dissociation laser induced fluorescence (TD-LIF), and supporting
chemical and meteorological measurements at Big Hill (1860 m), a high
elevation site in California's Sierra Nevada Mountains, are described. From
May through October, terrain-driven winds in the region routinely bring air
from Sacramento, 100 km southwest of the site, upslope over oak and pine
forests to Big Hill during the day, while at night, the site often samples
clean, dry air characteristic of the free troposphere. Winter differs mainly
in that the meteorology does not favour the buildup of Sacramento's
pollution over the Sierra Nevada range, and the urban-influenced air that is
seen has been less affected by biogenic VOC emissions, resulting in longer
lifetime for NO2 and a predominance of the inorganic forms of nitrogen
oxides.
Summertime observations at Big Hill can be compared with those from Granite
Bay, a Sacramento suburb, and from the University of California's Blodgett
Forest Research Station to examine the evolution of nitrogen oxides and
ozone within the urban plume. Nitrogen oxide radicals (NO and NO2),
which dominate total nitrogen oxides (NOy) at Granite Bay, are rapidly
converted into HNO3, ΣPNs, and ΣANs, such that these
compounds contribute 29, 30, and 21% respectively to the NOy budget
in the plume at Big Hill. Nevertheless, the decreasing concentrations of
NO2 as the plume is advected to Big Hill lead to decreases in the
production rate of HNO3 and ozone. The data also demonstrate the role
that temperature plays in sequestering NO2 into peroxy nitrates,
effectively decreasing the rate of ozone production. The important
contribution of ΣANs to NOy in the region suggests that they
should be considered with regards to export of NOy from the boundary
layer. Nocturnal observations of airmasses characteristic of the free
troposphere showed lower NOy concentrations, which were dominated by
HNO3 with a relatively small contribution from the organic nitrates. |
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