Messungen von Wasserstoffperoxid und organischen Hydroperoxiden am Schauinsland im Schwarzwald: ein Beitrag zur Charakterisierung der limitierenden Faktoren bei der Ozonproduktion
- Publisher: Forschungszentrum Jülich
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.