LE STUDIUM RESEARCH FELLOW / ARD 2020 - PIVOTS Programme
Dr Abdelwahid Mellouki & Dr Véronique Daële
Experimental measurements of atmospheric chemical reactions
The goal of this project is to obtain accurate and precise data on the rates and products associated with chemical reactions occurring in the atmosphere, using a wide variety of measurement techniques available at ICARE. Some of these measurements are challenging and the fellow will be required to utilize his experience to try to address long-standing uncertainties within atmospheric chemistry. He will also helping to develop experimental protocols and techniques at the host laboratory.
Achievements so far: The fellow has been focussing on the reaction of sulphur dioxide with the OH radical. This is a very important reaction in atmosphere, since it leads to the formation of sulphuric acid, which is of crucial importance to aerosol formation, and therefore has a major effect in terms of air pollution and climate change. However, there remain some key uncertainties in this reaction rate, primarily related to the effect of pressure on this reaction. To begin with, a thorough survey of the literature regarding this reaction was performed, and the gaps in the knowledge were assessed. Accordingly the fellow has conducted a series of careful measurements in the presence of a variety of bath gases (helium, nitrogen and argon) using the pulsed laser photolysis–laser induced fluorescence (PLP-LIF) technique. The maximum pressure available to the PLP-LIF technique is ~400 Torr (below atmsopheric pressure), and therefore to complement this technique, a series of simulation chamber measurements have been made in the presence of nitrogen, oxygen, argon and air at 760 Torr. By measuring this reaction using different techniques over a wide range of conditions, we have made definitive progress regarding understanding the pressure dependence of this reaction. This allows us to compare with previous measurements, and to determine, which, if any, are accurate. It is expected that this work will result in a publication that will be of interest to the atmospheric chemical community. The fellow has also taken the responsibility of instructing a PhD student, Ms. Hajar Elothmani, in atmospheric chemistry and the techniques involved in making accurate gas-phase kinetic measurements.