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@ARTICLE{Lu:20026,
      author       = {Lu, K.D. and Rohrer, F. and Holland, F. and Fuchs, H. and
                      Bohn, B. and Brauers, T. and Chang, C.C. and Häseler, R.
                      and Hu, M. and Kita, K. and Kondo, Y. and Li, X. and Lou,
                      S.R. and Nehr, S. and Shao, M. and Zeng, L.M. and Wahner, A.
                      and Zhang, Y.H. and Hofzumhaus, A.},
      title        = {{O}bservation and modelling of {OH} and {HO}2
                      concentrations in the {P}earl {R}iver {D}elta 2006: a
                      missing {OH} source in a {VOC} rich atmosphere},
      journal      = {Atmospheric chemistry and physics},
      volume       = {12},
      issn         = {1680-7316},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {PreJuSER-20026},
      pages        = {1541-1569},
      year         = {2012},
      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).},
      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.},
      keywords     = {J (WoSType)},
      cin          = {IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {Atmosphäre und Klima},
      pid          = {G:(DE-Juel1)FUEK491},
      shelfmark    = {Meteorology $\&$ Atmospheric Sciences},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000300656500021},
      doi          = {10.5194/acp-12-1541-2012},
      url          = {https://juser.fz-juelich.de/record/20026},
}