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| Titel |
Missing OH source in a suburban environment near Beijing: observed and modelled OH and HO2 concentrations in summer 2006 |
| VerfasserIn |
K. D. Lu, A. Hofzumahaus, F. Holland, B. Bohn, T. Brauers, H. Fuchs, M. Hu, R. Häseler, K. Kita, Y. Kondo, X. Li, S. R. Lou, A. Oebel, M. Shao, L. M. Zeng, A. Wahner, T. Zhu, Y. H. Zhang, F. Rohrer |
| 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 ; 13, no. 2 ; Nr. 13, no. 2 (2013-01-25), S.1057-1080 |
| Datensatznummer |
250017616
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| Publikation (Nr.) |
 copernicus.org/acp-13-1057-2013.pdf |
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| Zusammenfassung |
| Measurements of ambient OH and HO2 radicals were performed by laser
induced fluorescence (LIF) during CAREBeijing2006 (Campaigns of Air Quality
Research in Beijing and Surrounding Region 2006) at the suburban site Yufa in
the south of Beijing in summer 2006. On most days, local air chemistry was
influenced by aged air pollution that was advected by a slow, almost stagnant
wind from southern regions. Observed daily concentration maxima were in the
range of (4–17) × 106 cm−3 for OH and
(2–24) × 108 cm−3 for HO2 (including an estimated
interference of 25% from RO2). During daytime, OH reactivities were
generally high (10–30 s−1) and mainly contributed by observed VOCs and
their calculated oxidation products. The comparison of modelled and measured
HOx concentrations reveals a systematic underprediction of OH as a
function of NO. A large discrepancy of a factor 2.6 is found at the lowest NO
concentration encountered (0.1 ppb), whereas the discrepancy becomes
insignificant above 1 ppb NO. This study extends similar observations from
the Pearl-River Delta (PRD) in South China to a more urban environment. The
OH discrepancy at Yufa can be resolved, if NO-independent additional OH
recycling is assumed in the model. The postulated Leuven Isoprene Mechanism
(LIM) has the potential to explain the gap between modelled and measured OH
at Beijing taking into account conservative error estimates, but lacks
experimental confirmation. This and the hereby unresolved discrepancy at PRD
suggest that other VOCs besides isoprene might be involved in the required,
additional OH recycling. Fast primary production of ROx radicals up
to 7 ppb h−1 was determined at Beijing which was dominated by the
photolysis of O3, HONO, HCHO, and dicarbonyls. For a special case, 20 August,
when the plume of Beijing city was encountered, a missing primary
HOx source (about 3 ppb h−1) was determined under high
NOx conditions similar to other urban areas like Mexico City.
CAREBeijing2006 emphasizes the important role of OVOCs as a radical source
and sink, and the need for further investigation of the chemical degradation
of VOCs in order to better understand radical chemistry in VOC-rich air. |
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