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@ARTICLE{Albrecht:862048,
      author       = {Albrecht, Sascha R. and Novelli, Anna and Hofzumahaus,
                      Andreas and Kang, Sungah and Baker, Yare and Mentel, Thomas
                      and Wahner, Andreas and Fuchs, Hendrik},
      title        = {{M}easurements of hydroperoxy radicals
                      $({HO}\<sub\>2\</sub\>)$ at atmospheric concentrations using
                      bromide chemical ionisation mass spectrometry},
      journal      = {Atmospheric measurement techniques},
      volume       = {12},
      number       = {2},
      issn         = {1867-8548},
      address      = {Katlenburg-Lindau},
      publisher    = {Copernicus},
      reportid     = {FZJ-2019-02414},
      pages        = {891 - 902},
      year         = {2019},
      abstract     = {Hydroxyl and hydroperoxy radicals are key species for the
                      understanding of atmospheric oxidation processes. Their
                      measurement is challenging due to their high reactivity;
                      therefore, very sensitive detection methods are needed.
                      Within this study, the measurement of hydroperoxy radicals
                      (HO2) using chemical ionisation combined with a
                      high-resolution time-of-flight mass spectrometer (Aerodyne
                      Research Inc.) employing bromide as the primary ion is
                      presented. The sensitivity reached is equal to 0.005×108
                      HO2 cm−3 for 106 cps of bromide and 60 s of
                      integration time, which is below typical HO2 concentrations
                      found in the atmosphere. The detection sensitivity of the
                      instrument is affected by the presence of water vapour.
                      Therefore, a water-vapour-dependent calibration factor that
                      decreases approximately by a factor of 2 if the water vapour
                      mixing ratio increases from $0.1 \%$ to $1.0 \%$ needs
                      to be applied. An instrumental background, most likely
                      generated by the ion source that is equivalent to a HO2
                      concentration of (1.5±0.2)×108 molecules cm−3, is
                      subtracted to derive atmospheric HO2 concentrations. This
                      background can be determined by overflowing the inlet with
                      zero air. Several experiments were performed in the
                      atmospheric simulation chamber SAPHIR at the
                      Forschungszentrum Jülich to test the instrument performance
                      in comparison to the well-established laser-induced
                      fluorescence (LIF) technique for measurements of HO2. A
                      highly linear correlation coefficient of R2=0.87 is
                      achieved. The slope of the linear regression of 1.07
                      demonstrates the good absolute agreement of both
                      measurements. Chemical conditions during experiments allowed
                      for testing the instrument's behaviour in the presence of
                      atmospheric concentrations of H2O, NOx, and O3. No
                      significant interferences from these species were observed.
                      All of these facts demonstrate a reliable measurement of HO2
                      by the chemical ionisation mass spectrometer presented.},
      cin          = {IEK-8},
      ddc          = {550},
      cid          = {I:(DE-Juel1)IEK-8-20101013},
      pnm          = {899 - ohne Topic (POF3-899)},
      pid          = {G:(DE-HGF)POF3-899},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000458115600002},
      doi          = {10.5194/amt-12-891-2019},
      url          = {https://juser.fz-juelich.de/record/862048},
}