Journal Article

PreJuSER-20026

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Observation and modelling of OH and HO2 concentrations in the Pearl River Delta 2006: a missing OH source in a VOC rich atmosphere

Lu, K. D.FZJ* ; Rohrer, F.FZJ* ; Holland, F.FZJ* ; Fuchs, H.FZJ* ; Bohn, B.FZJ* ; Brauers, T.FZJ* ; Chang, C. C. ; Häseler, R.FZJ* ; Hu, M. ; Kita, K. ; Kondo, Y. ; Li, X.FZJ* ; Lou, S. R.FZJ* ; Nehr, S.FZJ* ; Shao, M. ; Zeng, L. M. ; Wahner, A.FZJ* ; Zhang, Y. H. ; Hofzumhaus, A.FZJ*

2012
EGU Katlenburg-Lindau

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Please use a persistent id in citations: http://hdl.handle.net/2128/7418  doi:10.5194/acp-12-1541-2012

Abstract: Ambient OH and HO2 concentrations were measured by laser induced fluorescence (LIF) during the PRIDE-PRD2006 (Program of Regional Integrated Experiments of Air Quality over the Pearl River Delta, 2006) campaign at a rural site downwind of the megacity of Guangzhou in Southern China. The observed OH concentrations reached daily peak values of (15-26) x 10(6) cm(-3) which are among the highest values so far reported for urban and suburban areas. The observed OH shows a consistent high correlation with j((OD)-D-1) over a broad range of NOx conditions. The correlation cannot be reproduced by model simulations, indicating that OH stabilizing processes are missing in current models. The observed OH exhibited a weak dependence on NOx in contrast to model predictions. While modelled and measured OH agree well at NO mixing ratios above 1 ppb, a continuously increasing underprediction of the observed OH is found towards lower NO concentrations, reaching a factor of 8 at 0.02 ppb NO. A dependence of the modelled-to-measured OH ratio on isoprene cannot be concluded from the PRD data. However, the magnitude of the ratio fits into the isoprene dependent trend that was reported from other campaigns in forested regions. Hofzumahaus et al. (2009) proposed an unknown OH recycling process without NO, in order to explain the high OH levels at PRD in the presence of high VOC reactivity and low NO. Taking a recently discovered interference in the LIF measurement of HO2 into account, the need for an additional HO2 -> OH recycling process persists, but the required source strength may be up to 20% larger than previously determined. Recently postulated isoprene mechanisms by Lelieveld et al. (2008) and Peeters and Muller (2010) lead to significant enhancements of OH expected for PRD, but an underprediction of the observed OH by a factor of two remains at low NO (0.1-0.2 ppb). If the photolysis of hydroperoxy aldehydes from isoprene is as efficient as proposed by Peeters and Muller (2010), the corresponding OH formation at PRD would be more important than the primary OH production from ozone and HONO. While the new isoprene mechanisms need to be confirmed by laboratory experiments, there is probably need for other, so far unidentified chemical processes to explain entirely the high OH levels observed in Southern China.

Keyword(s): J

Note: We thank the PRIDE-PRD2006 campaign team (2002CB410801), especially F. Yang, H. Su, A. Nowak, N. Takegawa, and A. Oebel for help and support at the field site. We thank P. H. Xie, Anhui Institute of Optics and Fine Mechanics in Hefei, China, for providing the methane data. We acknowledge financial support by the National Natural Science Foundation of China (Major Program: 21190052) and by EU-project PEGASOS (grant no. 265307).

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Contributing Institute(s):

1. Troposphäre (IEK-8)

Research Program(s):

1. Atmosphäre und Klima (P23)

Appears in the scientific report 2012

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Database coverage:
; ; ; ; Current Contents - Social and Behavioral Sciences ; JCR ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Thomson Reuters Master Journal List ; Web of Science Core Collection

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