Verlag des Forschungszentrums Jülich
JUEL-3597
At the beginning of the campaign, relatively large differences in the
calibration of the Luminol-chemiluminescence instruments used for
detection of the NO2 from the chemical amplifiers were found for some
groups. A meaningful comparison of the radical measurements thus required
harmonisation of the NO2 standards. This was achieved by tying all NO2
measurements to the NO2 calibration of the TOR station and by adopting a
common procedure for taking the non-linear response of the Luminol
detector into account. Thereafter, the different chemical amplifiers and
MIESR agreed within (30% for measurements of HO2 radicals produced
artificially by H2O photolysis. Somewhat larger discrepancies were found
for a comparison with CH3O2 radicals produced by
photolysis of CH3I and for CH3COO2 radicals produced by thermolysis of PAN.
In ambient air, all instruments found similar diurnal variations in the
RO2 concentrations, with maximum concentrations around or shortly after
noon time. The correlation was best under situations with high wind
speeds and low precursor concentrations. Overall, the chemical amplifiers
seemed to have less dynamic range than the MIESR, with the highest RO2
concentrations found by MIESR being underestimated by the chemical
amplifiers by up to a factor of 2. Possible explanations are a lower
conversion efficiency for large organic peroxy radicals and/or a strong
inverse dependence of the chain length on the relative humidity that was
found very recently in laboratory experiments and which was not accounted
for by the calibration procedures during PRICE. The decrease in
chainlength with increasing relative humidity would indeed bring the data
from the chemical amplifiers into much better agreement with MIESR. Given
the magnitude of the effect and its sensitivity to fluctuations in
ambient humidity and temperature, correction of the data in retrospect,
however, will be extremely difficult if not impossible.
Since high quality measurements of peroxy radicals can provide deep
insight in the degradation mechanism of organic compounds and
photo-oxidant formation, a vital interest remains in the further
development of the CA, including the conversion efficiencies for the
higher organic peroxy radicals and, most important, of the influence of
humidity on the chain length.
Volz-Thomas, Andreas; Arnold, T.; Behmann, T.; Borrell, P.; Borrell, P. M.; Burrows, J. P.; Cantrell, C. A.; Carpenter, L. J.; Clemitshaw, K. C.; Gilge, S.; Heitlinger, M.; Klüpfel, T.; Kramp, F.; Mihelcic, D.; Müsgen, P.; Pätz, H.- W.; Penkett, S. A.; Perner, D.; Schultz, M.; Shetter, R.; Slems, J.; Weissenmayer, M.
Peroxy Radical Inter Comparison Exercise (PRICE)
133 S., 1998
PRICE was organised as a formal comparison of different methods to
measure peroxy radicals (HO2 and RO2). It was conducted in summer 1994 at
the TOR(*1)-station Schauinsland in South-West Germany as a task of the
EU-project OCTA(*2). The comparison involved matrix isolation ESR
spectroscopy (MIESR) and five chemical amplifiers (CA). The campaign
lasted 5 weeks, with ambient measurements being performed over a time
period of 2 weeks. Between and after the ambient measurements, the
different calibration procedures used for the chemical amplifiers were
compared. Data delivery was performed after a formal data protocol.
Neuerscheinungen
Schriften des Forschungszentrums Jülich
Ihre Ansprechperson
Heike Lexis
+49 2461 61-5367
zb-publikation@fz-juelich.de