Kinetics and mechanistic studies in the HIRAC chamber

Atmospheric chambers are integral in the understanding of key issues surrounding the atmosphere. Atmospheric chemical processes can be studied both kinetically and mechanistically under predetermined and controlled conditions to better understand VOC oxidation processes occurring in the atmosphere. Wide arrays of atmospheric chambers enable the underpinning of key issues surrounding the behaviour of atmospheric trace gases and aerosols. Moreover, their input has also spread increasingly into mechanism development and development of new methods for detecting and investigating trace gases by intercomparison of different measuring instruments. The Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) chamber at the University of Leeds is a 2.25 m3 stainless steel reactor that allows the study of a wide range of kinetics and mechanistic investigations over the full range of tropospheric temperatures and pressures. A temperature control system has been setup and tested in HIRAC. Absolute rate measurements ozonolysis reactions with propene were performed over a temperature range of 220 – 320 K to characterise this system. Relative rate measurements have also been used to measure the kinetics of a number of reactions, using Gas Chromatography (GC-FID) and Fourier Transform Infra-red (FTIR) spectrometry detection. An investigation of chlorine atom reactions with butanes and pentanes over a similar temperature range relevant to the entire troposphere were performed and branching ratios calculated over varying temperatures using GC and FTIR detection. High precision measurements were also obtained for several chlorine atom reactions and the rate coefficients of a series of higher ketones, esters and alkanes were generated in HIRAC using this method. GC-FID and FTIR were also useful in a preliminary investigation on the reaction of chlorine atoms with ethanol, and initial results on HCl and DCl ratios were obtained from this study. Relative rate experiments were also useful in the assessment of different OH radical generation techniques under low NOx conditions. A characterisation of tert-butyl hydroperoxide photolysis in HIRAC was performed under low NOx conditions utilising the HIRAC FAGE for absolute OH measurements.