Actinometric measurements of NO2 photolysis frequencies in the atmosphere simulation chamber SAPHIR

[摘要] The simulation chamber SAPHIR at Forschungszentrum Jülichhas UV permeable teflon walls facilitating atmosphericphotochemistry studies under the influence of natural sunlight.Because the internal radiation field is strongly affected byconstruction elements, we use external, radiometric measurementsof spectral actinic flux and a model to calculate mean photolysisfrequencies for the chamber volume Bohn04B. In this workwe determine NO₂ photolysis frequencies j(NO₂) withinSAPHIR using chemical actinometry by injecting NO₂ andobserving the chemical composition during illumination undervarious external conditions. In addition to a photo-stationaryapproach, a time-dependent method was developed to analyse thedata. These measurements had two purposes. Firstly, to check themodel predictions with respect to diurnal and seasonal variationsin the presence of direct sunlight and secondly to obtain anabsolute calibration factor for the combined radiometry-modelapproach. We obtain a linear correlation between calculated andactinometric j(NO₂). A calibration factor of 1.34±0.10is determined, independent of conditions in good approximation.This factor is in line with expectations and can be rationalisedby internal reflections within the chamber. Taking into accountthe uncertainty of the actinometric j(NO₂), an accuracy of13% 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 wasdetermined for the NO+O₃ reaction at 298K usinganalytical and numerical methods of data analysis.

[学科分类] 大气科学