Actinometric measurements of NO<sub>2</sub> photolysis frequencies in the atmosphere simulation chamber SAPHIR

Abstract

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 (Bohn and Zilken, 2005). In this work we determine NO 2 photolysis frequencies j (NO 2 ) within SAPHIR using chemical actinometry by injecting NO 2 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 radiometrymodel approach. We obtain a linear correlation between calculated and actinometric j (NO 2 ). 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 (NO 2 ), an accuracy of 13% is estimated for the determination of j (NO 2 ) in SAPHIR. In separate dark experiments a rate constant of (1.93±0.12)×10 −14 cm 3 s −1 was determined for the NO+O 3 reaction at 298 K using analytical and numerical methods of data analysis.

Technical Note: Formal blind intercomparison of HO<sub>2</sub> measurements in the atmosphere simulation chamber SAPHIR during the HOxComp campaign

“…The chamber is in operation since 2001 and has been described in more detail elsewhere (e.g. Bohn et al, 2005;Rohrer et al, 2005;Wegener et al, 2007). The chamber was successfully used in a number of intercomparison experiments.…”

Comparison of N<sub>2</sub>O<sub>5</sub> mixing ratios during NO3Comp 2007 in SAPHIR

“…A description of the chamber and its properties can be found elsewhere Bohn et al, 2005). The chamber offers the possibility to investigate chemical processes under atmospheric conditions.…”

Comparison of OH concentration measurements by DOAS and LIF during SAPHIR chamber experiments at high OH reactivity and low NO concentration

“…The chamber air can be humidified by evaporating Milli-Q water, which is added together with a large flow of synthetic air. A more detailed description of the chamber and its properties can be found elsewhere Bohn et al, 2005).…”