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@ARTICLE{Bohn:49902,
      author       = {Bohn, B.},
      title        = {{S}olar spectral actinic flux and photolysis frequency
                      measurements in a deciduous forest},
      journal      = {Journal of Geophysical Research},
      volume       = {111},
      issn         = {0148-0227},
      address      = {Washington, DC},
      publisher    = {Union},
      reportid     = {PreJuSER-49902},
      pages        = {D15303},
      year         = {2006},
      note         = {Record converted from VDB: 12.11.2012},
      abstract     = {[ 1] Within the Emission and Chemical Transformation of
                      Biogenic Volatile Organic Compounds ( ECHO) project the
                      photochemistry of biogenic organic compounds in a forest was
                      investigated. In this context, two spectroradiometers were
                      used to determine solar spectral actinic flux and photolysis
                      frequencies within and above a deciduous forest at Julich,
                      Germany. Locations in the forest and in a small clearing
                      were examined 2 m above ground. Under overcast conditions,
                      photolysis frequencies were within 1 - $3\%$ and 6 - $8\%$
                      of above canopy values at forest and clearing locations,
                      respectively. In a spectral range below 500 nm the canopy
                      was found to act as a gray filter that diminished spectral
                      actinic flux independent of daytime and wavelength. Under
                      clear-sky conditions, diurnal variations within the forest
                      also followed that of diffuse sky radiation above the forest
                      except for sharp peaks from direct sunlight that was
                      incident sporadically at the selected locations. The results
                      under all conditions were in accord with the foliage being
                      opaque toward UV and gaps in the canopy being responsible
                      for the remaining actinic flux. Sky photographs showed that
                      the distribution and size of gaps in the foliage were
                      extremely heterogeneous with patterns changing rapidly upon
                      changing location. Regarding daytime chemical reactions of
                      biogenic compounds within the forest, it was estimated that
                      degradation by OH was reduced by a factor similar to the
                      photolysis frequencies, while potential degradation by NO3
                      was increased by a factor of similar to 3 compared with
                      above forest conditions. As a result, it was estimated that
                      minor fractions of $0.8\%$ of isoprene and $3.4\%$ of
                      monoterpenes were degraded by reactions with OH, NO3, and
                      O-3 prior to transport into the layer above the forest.},
      keywords     = {J (WoSType)},
      cin          = {ICG-II},
      ddc          = {550},
      cid          = {I:(DE-Juel1)VDB48},
      pnm          = {Atmosphäre und Klima},
      pid          = {G:(DE-Juel1)FUEK406},
      shelfmark    = {Meteorology $\&$ Atmospheric Sciences},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000239786800010},
      doi          = {10.1029/2005JD006902},
      url          = {https://juser.fz-juelich.de/record/49902},
}