Dwayne Heard

Research section: Physical Chemistry

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

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, and comparison with model calculations. OH removes almost all trace gases, and drives much of the chemistry of the atmosphere, (2) laboratory studies of the kinetics and photochemistry of key atmospheric reactions, using a variety of laser-based methods, and (3) studies of atmospheric chemistry within the HIRAC chamber under simulated conditions.

Field measurements of OH, HO₂ and IO free-radicals in the atmosphere on ground and airborne platforms
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 ~20 field campaigns worldwide (including Antarctica, the Arctic, Borneo, Africa, Tasmania and Cape Verde) and future campaigns are planned in a variety of chemical environments, for example in central London and the Western Pacific in 2011/12. Measurements are compared with calculations from a range of models, including a box model utilitising the Master Chemical Mechanism, which was developed at Leeds and currently contains up to 15,000 reactions and over 5000 chemical species. 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 reactivity of OH, which was recently deployed in Borneo, and new instruments are under development for other species, for example, peroxy radicals.

Laboratory 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, for example Titan. Heterogeneous aerosol chemistry is also an important component of chemical models and we are measuring the uptake of radicals onto the surface of aerosols of differing size distributions and chemical composition.

Kinetic and mechanistic studies using The Leeds Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC)
HIRAC enables us to study mechanistic details of the oxidative chemistry and photochemistry of our atmosphere whilst controlling the chemical composition and conditions (e.g. temperature and pressure). Using a variety of state-of-the art instruments we are able to detect both stable species and free-radicals, including OH, HO₂ and NO₃ radicals, and comparison with model predictions confirms our mechanistic understanding. HIRAC also provides an ideal medium in which to calibrate field instruments under realistic conditions and is a testbed to develop new instruments.

The work is supported by the National Centre for Atmospheric Science (NCAS) which is based in Leeds and funded by NERC. Much of the work is performed in collaboration with colleagues here in Chemistry and also 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. Further information can be found on the links below.

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FAGE group    Publications    Book published    HIRAC chamber

SELECTED PUBLICATIONS

L. K. Whalley, K. L. Furneaux, A. Goddard, J. D. Lee, A. Mahajan, H. Oetjen, K. A. Read, N. Kaaden, L. J. Carpenter, A. C. Lewis, J. M. C. Plane, E. S. Saltzman, A. Wiedensohler, and D. E. Heard, The chemistry of OH and HO2 radicals in the boundary layer over the tropical Atlantic Ocean, Atmos. Chem. Phys. Discuss., 9, 15959-16009, 2009.

T. Ingham, A. Goddard, L. K. Whalley, K. L. Furneaux, P. M. Edwards, C. P. Seal, D. E. Self, G. P. Johnson, K. A. Read, J. D. Lee and D. E. Heard, A flow-tube based laser-induced fluorescence instrument to measure OH reactivity in the troposphere, Atmos. Meas. Tech. Discuss., 2, 1–37, 2009

K. L. Furneaux, L. K. Whalley, D. E. Heard, H. M. Atkinson, W. J. Bloss, M. J. Flynn, M. W. Gallagher, T. Ingham, L. Kramer, J. D. Lee, R. Leigh, G. B. McFiggans, A. S. Mahajan, P. S. Monks, H. Oetjen, J. M. C. Plane, and J. Whitehead, Measurements of iodine monoxide at a semi polluted coastal location, Atmos. Chem. Phys. Discuss., 9, 25737–25797, 2009

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., 10, 422-437, 2008