Actinometric measurements of NO2 photolysis frequencies in the atmosphere simulation chamber SAPHIR B. Bohn, F. Rohrer, T. Brauers, and A. Wahner Institut für Chemie und Dynamik der Geosphäre II: Troposphäre, Forschungszentrum Jülich, 52425 Jülich, Germany
Abstract. The simulation chamber SAPHIR at Forschungszentrum Jülich
has UV permeable teflon walls facilitating atmospheric
photochemistry studies under the influence of natural sunlight.
Because the internal radiation field is strongly affected by
construction elements, we use external, radiometric measurements
of spectral actinic flux and a model to calculate mean photolysis
frequencies for the chamber volume Bohn04B. In this work
we determine NO2 photolysis frequencies j(NO2) within
SAPHIR using chemical actinometry by injecting NO2 and
observing the chemical composition during illumination under
various external conditions. In addition to a photo-stationary
approach, a time-dependent method was developed to analyse the
data. These measurements had two purposes. Firstly, to check the
model predictions with respect to diurnal and seasonal variations
in the presence of direct sunlight and secondly to obtain an
absolute calibration factor for the combined radiometry-model
approach. We obtain a linear correlation between calculated and
actinometric j(NO2). A calibration factor of 1.34±0.10
is determined, independent of conditions in good approximation.
This factor is in line with expectations and can be rationalised
by internal reflections within the chamber. Taking into account
the uncertainty of the actinometric j(NO2), an accuracy of
13% is estimated for the determination of j(NO2) in SAPHIR.
In separate dark experiments a rate constant of
(1.93±0.12)x10-14 cm3 s-1 was
determined for the NO+O3 reaction at 298K using
analytical and numerical methods of data analysis.
Citation: Bohn, B., Rohrer, F., Brauers, T., and Wahner, A.: Actinometric measurements of NO2 photolysis frequencies in the atmosphere simulation chamber SAPHIR, Atmos. Chem. Phys., 5, 493-503, doi:10.5194/acp-5-493-2005, 2005.