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@ARTICLE{Tan:866650,
      author       = {Tan, Zhaofeng and Lu, Keding and Hofzumahaus, Andreas and
                      Fuchs, Hendrik and Bohn, Birger and Holland, Frank and Liu,
                      Yuhan and Rohrer, Franz and Shao, Min and Sun, Kang and Wu,
                      Yusheng and Zeng, Limin and Zhang, Yinsong and Zou, Qi and
                      Kiendler-Scharr, Astrid and Wahner, Andreas and Zhang,
                      Yuanhang},
      title        = {{E}xperimental budgets of {OH}, {HO} 2 , and {RO} 2
                      radicals and implications for ozone formation in the {P}earl
                      {R}iver {D}elta in {C}hina 2014},
      journal      = {Atmospheric chemistry and physics},
      volume       = {19},
      number       = {10},
      issn         = {1680-7324},
      address      = {Katlenburg-Lindau},
      publisher    = {EGU},
      reportid     = {FZJ-2019-05729},
      pages        = {7129 - 7150},
      year         = {2019},
      abstract     = {Hydroxyl (OH) and peroxy radicals (HO2 and RO2) were
                      measured in the Pearl River Delta, which is one of the most
                      polluted areas in China, in autumn 2014. The radical
                      observations were complemented by measurements of OH
                      reactivity (inverse OH lifetime) and a comprehensive set of
                      trace gases including carbon monoxide (CO), nitrogen oxides
                      (NOx=NO, NO2) and volatile organic compounds (VOCs). OH
                      reactivity was in the range from 15 to 80 s−1, of which
                      about $50 \%$ was unexplained by the measured OH
                      reactants. In the 3 weeks of the campaign, maximum median
                      radical concentrations were 4.5×106 cm−3 for OH at noon
                      and 3×108 and 2.0×108 cm−3 for HO2 and RO2,
                      respectively, in the early afternoon. The completeness of
                      the daytime radical measurements made it possible to carry
                      out experimental budget analyses for all radicals (OH, HO2,
                      and RO2) and their sum (ROx). The maximum loss rates for OH,
                      HO2, and RO2 reached values between 10 and 15 ppbv h−1
                      during the daytime. The largest fraction of this can be
                      attributed to radical interconversion reactions while the
                      real loss rate of ROx remained below 3 ppbv h−1.
                      Within experimental uncertainties, the destruction rates of
                      HO2 and the sum of OH, HO2, and RO2 are balanced by their
                      respective production rates. In case of RO2, the budget
                      could be closed by attributing the missing OH reactivity to
                      unmeasured VOCs. Thus, the presumption of the existence of
                      unmeasured VOCs is supported by RO2 measurements. Although
                      the closure of the RO2 budget is greatly improved by the
                      additional unmeasured VOCs, a significant imbalance in the
                      afternoon remains, indicating a missing RO2 sink. In case of
                      OH, the destruction in the morning is compensated by the
                      quantified OH sources from photolysis (HONO and O3),
                      ozonolysis of alkenes, and OH recycling (HO2+NO). In the
                      afternoon, however, the OH budget indicates a missing OH
                      source of 4 to 6 ppbv h−1. The diurnal variation of
                      the missing OH source shows a similar pattern to that of the
                      missing RO2 sink so that both largely compensate each other
                      in the ROx budget. These observations suggest the existence
                      of a chemical mechanism that converts RO2 to OH without the
                      involvement of NO, increasing the RO2 loss rate during the
                      daytime from 5.3 to 7.4 ppbv h−1 on average. The
                      photochemical net ozone production rate calculated from the
                      reaction of HO2 and RO2 with NO yields a daily integrated
                      amount of 102 ppbv ozone, with daily integrated ROx
                      primary sources being 22 ppbv in this campaign. The
                      produced ozone can be attributed to the oxidation of
                      measured $(18 \%)$ and unmeasured $(60 \%)$
                      hydrocarbons, formaldehyde $(14 \%),$ and CO $(8 \%).$
                      An even larger integrated net ozone production of 140 ppbv
                      would be calculated from the oxidation rate of VOCs with OH
                      if HO2 and all RO2 radicals react with NO. However, the
                      unknown RO2 loss (evident in the RO2 budget) causes
                      30 ppbv less ozone production than would be expected from
                      the VOC oxidation rate.},
      cin          = {IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {243 - Tropospheric trace substances and their
                      transformation processes (POF3-243)},
      pid          = {G:(DE-HGF)POF3-243},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000469430600001},
      doi          = {10.5194/acp-19-7129-2019},
      url          = {https://juser.fz-juelich.de/record/866650},
}