Dwayne Heard

Research section: Physical Chemistry

KEYWORDS Atmospheric chemistry Field measurements Hydroxyl radicals Laser induced fluorescence spectroscopy Reaction kinetics and photochemistry Chamber studies

RESEARCH INTERESTS

The future well-being of our atmosphere relies on a detailed understanding of the chemistry responsible for the oxidation of man-made and natural emissions. Numerical models are used to predict future changes in global warming and air quality, and drive all legislative controls on emissions. Our research aims to improve the accuracy of the chemistry contained in these models through (1) field measurements in the atmosphere of key intermediates, for example, the hydroxyl radical, OH, which removes almost all trace gases, and drives almost all of the chemistry, and (2) laboratory and smog chamber studies of the kinetics and photochemistry of key atmospheric reactions.

Field measurements of OH, HO₂ and IO free-radicals in the atmosphere
State-of-the-art instruments using laser-induced fluorescence spectroscopy at low pressure (FAGE) have been developed for quantitative measurement of the hydroxyl radical (OH), hydroperoxy radical HO₂ and iodine oxide radical (IO), both from ground-based mobile laboratories and the NERC FAAM BAe-146 instrumented aircraft. Since 1996 we have participated in 17 field campaigns worldwide (including Antarctica, Africa, Tasmania and Cape Verde) and future campaigns in 2008 include the Arctic (Hudson Bay) and the Tropics (Borneo rainforest and Cape Verde Islands). Measurements are compared with calculations from a range of models, including the Master Chemical Mechanism, which was developed at Leeds and currently contains up to 15,000 reactions. The level of agreement with models is an excellent test of how well we understand the chemistry of our atmosphere for different environments. We have also developed a new instrument to measure the chemical lifetime of OH, and new isntruments are under development.

Laboratory and smog chamber studies of chemical kinetics and photochemistry
Each reaction in an atmospheric model requires a rate coefficient and branching ratio for the products to be specified as a function of temperature and pressure, and also wavelength in the case of photochemical reactions. In the well-equipped Dainton kinetics laboratory we use laser flash-photolysis combined with a variety of laser spectroscopic probes to study the details of key chemical and photochemical atmospheric processes, many of which involve free-radicals. Using a pulsed Laval nozzle we are able to access temperatures are low as 50K which are representative of the atmosphere of other planets and moons. The Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC) enables us to study our atmosphere whilst controlling the chemical composition, and by using a variety of state-of-the art instruments we are able to detect both stable species and free-radicals, including OH, the latter using FAGE.

Much of the work is performed in collaboration with colleagues in Chemistry (Seakins, Plane and Pilling) and in the School of the Environment, with whom there are a number of joint grants. Our research is highly collaborative, and we have very close links with other atmospheric groups within the University and across the wider UK and international community.

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FAGE group    Book published    HIRAC chamber   

SELECTED PUBLICATIONS

Measurement of OH and HO2 in the troposphere. D. E. Heard and M. J. Pilling, Chemical Reviews, 103, 5163-5198 (2003)

Detection of iodine monoxide radicals in the marine boundary layer using laser induced fluorescence spectroscopy, L.K. Whalley, K.L. Furneaux, T. Gravestock, H.M. Atkinson, C.S.E. Bale, T. Ingham, W.J. Bloss, D.E. Heard, Journal of Atmospheric Chemistry., 58, 19-39 (2007)

Observations of OH and HO2 radicals in coastal Antarctica, W. J. Bloss, J. D. Lee, D. E. Heard, R. A. Salmon, S. J.-B. Bauguitte, H. K. Roscoe, and A. E. Jones, Atmospheric Chemistry and Physics., 7, 4171-4185, 2007.

Pulsed Laval nozzle study of the kinetics of OH with unsaturated hydrocarbons at very low temperatures, S.E. Taylor, A. Goddard, M.A. Blitz, P.A. Cleary and D.E. Heard, Physical Chemistry Chemical Physics., DOI: 10.1039/b711411g, 2008