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| Titel |
Long term measurements of NO3 radical at a semi-arid urban site: Extreme concentration events and their oxidation capacity |
| VerfasserIn |
David Asaf, Daniel Pedresen, Mordechai Peleg, Christoph Kern, Ulrich Platt, Menachem Luria |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250045585
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| Zusammenfassung |
| Nitrate radical (NO3), an important nighttime tropospheric oxidant, was measured
continuously for two years (July 2005-September 2007) in Jerusalem, a semi-arid urban site,
by long-path differential optical absorption spectroscopy (LP-DOAS). Joint measurements
with the University of Heidelberg’s LP-DOAS showed good agreement (r=0.94). Extreme
episodes of NO3 were measured during this period, with maximum mixing ratios above 800
ppt, two-fold greater than measured anywhere else. The unique chemistry of these extreme
levels is a consequence of several factors: (i) an increase in ozone concentrations parallel to a
substantial decrease in relative humidity during the night, (ii) mean nighttime NO2
levels above 10 ppbv preventing a deficiency in NO3 precursors, (iii) negligible
NO levels during the night, and (iv) a substantial decrease in the loss processes
leading to lower degradation frequencies and allowing the NO3 lifetimes to build
up to a maximum mean of 25 minutes. The results indicate that for these extreme
events, the major sink pathway for NO3 was direct homogeneous gas phase reactions
with VOCs. We have found that compared to OH and O3, NO3 extreme events
are responsible for approximately 70% of the oxidation of total VOCs and nearly
75% of the olefinic VOCs, twice the oxidation potential of the OH radical for the
VOC’s. These results establish the NO3 radical as a significant atmospheric oxidant in
Jerusalem and as a predominant contributor to VOC degradation in urban atmospheres. |
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