Department of Chemistry

The motivation for my research is to understand the chemical and dynamical factors that determine changes in atmospheric composition. These are fascinating as scientific problems in their own right and are also important for global environmental issues such as stratospheric ozone depletion and climate change. In the past, scientists have concentrated on relatively short term chemical processes (seconds to weeks); it is now important than ever to understand how atmospheric composition is influenced by longer-term processes (weeks to years).

A wealth of measurements exists that has been collected in global monitoring networks, during focussed field campaigns and by satellite instruments. Great opportunities exist to exploit these data to understand a range of atmospheric problems. My approach is to analyse and interpret the available measurements, collaborating closely with the atmospheric modelling (Prof. Pyle) and measurement (Prof. Jones and Dr Kalberer) groups in the Chemistry Department. Given the global nature of the problems considered, international collaborations are important components of the work. Topics are being studied include:

• Stratospheric ozone depletion over northern mid-latitudes. Quantifying past ozone loss and particularly the relative importance of chemical depletion and dynamical influences is essential to understanding how stratospheric ozone will change in future;
• Winter-time chemical ozone loss over the Arctic. This is a major factor influencing ozone over mid-latitudes and varies greatly, with much greater losses in cold winters. Since the cold Arctic winters are getting colder, it is important to understand its relation to climate change;
• Transport of chemical species in the Tropics. The bulk of air entering the stratosphere does so in the Tropics. There are large natural (terrestrial and oceanic) and anthropogenic sources of trace chemicals into the Tropical atmosphere whose influence is not well known.

In addition to interpreting existing observations, I have a small group developing and constructing instruments capable of running autonomously in order to make observations for months and years at a time. These custom-built instruments will be used to make measurements of short-lived halocarbons and hydrocarbons at sites in the West Pacific (Malaysia, Taiwan, Australia and New Zealand) as well as on commercial container ships. There are very few measurements in these places and these instruments will operate for months and years. The observations are thus valuable in their own right, and are being used to estimate emissions of these compounds, which are important for ozone in the stratosphere and troposphere and possibly for particle formation over the remote oceans.

Selected Publications

• Micro-DIRAC: An Autonomous Instrument for Halocarbon Measurements, Atmos. Meas. Tech. , 3, 507-521, (2010)
• Bromocarbons in the tropical marine boundary layer at the Cape Verde Observatory – measurements and modeling, Atmos. Chem. Phys. , 9, 9083–9099, www.atmos-chem-phys.net/9/9083/2009/ (2009)
• Understanding the relation between Arctic ozone loss and the volume of polar stratospheric clouds, Int. J. Rem. Sens. , 30, 15, 4065-4070, (2009)
• The long history of ozone: Analyses of recent measurements, Twenty Years of Ozone Decline, Eds. C. Zerefos, G. Contopoulos and G. Skalkeas, Springer Publications, 111-117, (2009)
• SCOUT-O3/ACTIVE High-altitude Aircraft Measurements around Deep Tropical Convection, Bull. Am. Met. Soc. , 647-662, DOI:10.1175/BAMS-89-5-647, (2008)