Verlag des Forschungszentrums Jülich
JUEL-2998
Gilge, Stefan; Kley, Dieter; Volz-Thomas, Andreas; Geiß, Heiner
Messungen von Wasserstoffperoxid und organischen Hydroperoxiden am Schauinsland im Schwarzwald. Ein Beitrag zur Charakterisierung der limitierenden Faktoren bei der Ozonproduktion
166 S., 1995
Abstract
Continuous measurements ofH202and organic hydroperoxides were performed at the
field station Schauinsland between January 1989 and June 1991 using an ezyme catalysed
fluorescence instrument. The mixing ratios were in the range of the detection
limit (20 ppt) up to 4.4 ppb for ~Oz and 1.7 ppb for ROOR. Both Hz02 and ROOH
show a strong seasonal variation with maximum concentrations in summer. The observed
seasonal trend is in line with the photochemical formation mechanism on the
one hand and the main atmospheric loss processes on the other hand.
The mixing ratios ofHz02 and ROOH are strongly influenced by wet deposition. For
interpretation ofthe behavior ofthese substances in gas phase, this influence has to be
eliminated. This was achieved by selecting sunny periods from the whole data set.
In addition, periods were selected, where production exeeds chemical losses, because
then, the measured concentrations of photochemically produced species, in first approximation,
should reflect their production rates. This is the case when air masses
arrive at Schauinsland from the nearby city of Freiburg and Rhine valley during
summer and daytime.
Comparison of results of smog chamber experiments performed by Hess et al. (1992
a.b,c) with chemical box model calculations using the EURORADM mechanism
(Stockwell and Kley, 1994) showed, that a positive slope in the H20/Ox ratio with
increasing photochemical age is an indicator for NOx limitation of photochemical
ozone production. The box model was initialized using typical NOx start concentrations
and VOCINOx ratios for the Schauinsland site.
Analysis ofthe measured concentration ratios ofH202 and Ox versus the photochemical
age of the air masses gave the result, that a large fraction of these measurements
already fall into thecategory where theozone production isNOx limited.
For this analysis only data were used, where the station was influenced by fresh anthropogenic
emissions from Freiburg and the Rhine Valley, i.e. the analysed air masses
were exposed to anthropogenic emissions later than four hours before arrival at
the site. Since the advected air mass from other wind sectors are photochemically
further processed, because anthropogenic sources are more distant, it C3Jl be coneluded
that at Schauinsland the photochemical ozone production is in most cases limited
by the availibility ofNOx' Since Schauinsland is relative dose to a large anthropogenic
pollution source, this conclusion shoud be also valid for most rural areas in
Europe.
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