Atmospheric Chemistry and Physics
www.atmos-chem-phys.net
1680-7316
1680-7324
5
1
2005
10.5194/acp-5-191-2005
http://www.atmos-chem-phys.net/5/191/2005/
http://www.atmos-chem-phys.net/5/191/2005/acp-5-191-2005.html
http://www.atmos-chem-phys.net/5/191/2005/acp-5-191-2005.pdf
191
206
2005-01-25
Model-aided radiometric determination of photolysis frequencies in a sunlit atmosphere simulation chamber
B. Bohn
H. Zilken
Institut für Chemie und Dynamik der Geosphäre II: Troposphäre, Forschungszentrum Jülich, 52425 Jülich, Germany
Zentralinstitut für Angewandte Mathematik, Forschungszentrum Jülich, 52425 Jülich, Germany
In this work diurnal and seasonal variations of mean photolysis
frequencies for the atmosphere simulation chamber SAPHIR at
Forschungszentrum Jülich are calculated. SAPHIR has a complex
construction with UV permeable teflon walls allowing natural
sunlight to enter the reactor volume. The calculations are based
on external measurements of solar spectral actinic flux and a
model considering the time-dependent impact of shadows from
construction elements as well as the influence of the teflon
walls. Overcast and clear-sky conditions are treated in a
consistent way and different assumptions concerning diffuse sky
radiance distributions are tested. Radiometric measurements inside
the chamber are used for an inspection of model predictions. Under
overcast conditions we obtain fractions of 0.74 and 0.67 of
external values for photolysis frequencies <i>j</i>(NO<sub>2</sub>) (NO<sub>2</sub>+<i>h</i>ν→NO+O(<sup>3</sup>P)) and <i>j</i>(O<sup>1</sup>D)
(O<sub>3</sub>+<i>h</i>ν→O<sub>2</sub>+O(<sup>1</sup>D)), respectively. On a clear
sky summer day these values are time-dependent within ranges
0.65-0.86 and 0.60-0.73, for <i>j</i>(NO<sub>2</sub>) and <i>j</i>(O<sup>1</sup>D),
respectively. A succeeding paper (Bohn
et al., 2004) is dealing with
an on-road test of the model approach by comparison with
photolysis frequencies from chemical actinometry experiments
within SAPHIR.