Professor Alastair Lewis

01904 322522
Email: ally.lewis@york.ac.uk

Atmospheric Chemistry

Career summary

Alastair Lewis was appointed as professor of atmospheric chemistry at the University of York in 2006; previous to this he held the positions of Reader (at York) and Lecturer in the Schools of Chemistry and Environment at the University of Leeds. He completed a PhD at the University of Leeds using hyphenated chromatographic techniques for the analysis of urban and combustion particles, working subsequently on the development and application of chromatographic and mass spectrometric techniques for the measurement of organic compounds in the environment. He has participated in > 30 major atmospheric science field projects, from polar regions to tropical oceans, city centres to remote forests.

Alastair was awarded the Desty Memorial Prize for Innovation in Separation Science in 2001, a Philip Leverhulme Prize in Earth, Ocean and Atmospheric Science in 2004, the Royal Society of Chemistry SAC Silver Medal in 2006 and the 2012 Royal Society of Chemistry John Jeyes Award for Environment, Energy and Sustainability.

Alastair has more than 180 peer reviewed publications and book chapters, and was editor of the textbook Multidimensional Chromatography by John Wiley & Sons. He has held NERC, EPSRC, EU, Wolfson and Royal Society awards and was Principle Investigator on two major NERC consortium experimental atmospheric chemistry projects, TORCH and ITOP, the latter being the first experiment to use the FAAM146 aircraft.  Alastair is a member of a number of expert advisory groups, including for the Department of Business Innovation and Skills, the National Physical Laboratory, STFC, Defra and WMO. He is currently a member of the REF-2014 sub-panel 8 (Chemistry).

In addition to teaching and research at the University, Alastair is also currently Director for atmospheric composition at the National Centre for Atmospheric Science (NCAS), and also its Deputy Director. Between 2007 and 2013 he was seconded part-time as Technologies theme leader for the Natural Environment Research Council advising on its science and technology strategy and research investments.

Current research studies reactive organic carbon in the atmosphere and its contribution to global air pollution, the transport of pollutants in weather systems including regional and long range effects, inter-annual observations in the background atmosphere, composition and evolution of organic aerosols, theoretical and experimental approaches to high complexity mixtures, multidimensional and multiphase chromatography, microfluidics and miniaturised sensors, petrochemical composition and natural products analysis.

Alastair works extensively with industry translating atmospheric chemical technologies into other fields. Recent collaborations include joint research projects with Markes International, the National Physical Laboratory, MoD and DSTL, Valco VICI, BP and AWE.

Further details on the activities of research staff from the National Centre for Atmospheric Science, based in York.

Research summary

Gas phase atmospheric chemistry

The oxidation of organic compounds in the presence of NOx generates tropospheric ozone, a key component of photochemical smog and a regulated air pollutant. Whilst the basic mechanism of O3 formation in the troposphere is well established, there is much still to discover about how individual organic compounds participate in these processes, how the chemistry of VOCs and NOx varies in time and space, and how these chemicals may change in the future as a result of regulation, economic and energy policy, land-use or climate change  The man-made sources of VOCs are known reasonably well described in developed countries, but emissions from rapidly growing mega-cities are much less certain, and our research aims to constraint these emissions used advanced measurements from aircraft. [See for example our estimates for Lagos by Hopkins et al. Atmos. Chem. Phys, 9, 8471-8477, 2008]. Natural emissions are often even less well understood; some VOCs are released from vegatation, others by biomass burning or from the oceans. We recently estabilshed for example the global impacts of benzene released from forest fires [Lewis et al. Atmos. Chem. Phys. 13, 851-867, 2013].

Our research places significant emphasis on field measurements; often these are short term activities, typically for 4-8 weeks in the field, and PhDs almost always include some element of field work.

Chemical metrology

Detecting organic and inorganic chemicals in air can be a difficult task. The abundance of many species is often very low, sometimes only a few parts per trillion, and the ‘matrix’, air itself, can be highly highly complex, containing many tens of thousands of different species at trace levels. By developing higher reoslution methods of analysis we showed how complex urban air can be – the original concepts published back in 2000 in Lewis et al., Nature, 405, 778-781. This theme of research continues today developing high resolution methods for compound specific measurements of chemicals in air. This uses techniques such as thermal desorption, gas chromatography, mass spectrometry, often adapted for use in the field. We have developed instruments for long-term field deployment, operation from vehicles and a GC-MS instrument that flies on the FAAM146 research aircraft.

In addition, the NCAS research group based in York provides instruments and measurements for community use and supports the detection of VOCs in emergencies – for example quantifying the emissions from the Elgin North Sea gas platform leak in 2012.

Making measurements tracable to common international standards is essential if data collected by our research group are to be intepreted in combination with others. Research into standards and tracability for gas phase measurements is an activity that cuts across much of the atmospheric research at York, and we collaborate in international research activities coordinated by the World Meterological Organisation.

Organic aerosol composition

The uptake of organic material onto atmospheric particles and the coagulation of material to form new fine aerosol is an area of significant current interest, since organic aerosol make a significant contribution to total aerosol number as well as influencing hygroscopic properties and subsequent ability to act as cloud condensation nuclei. Toxicologically there is also evidence that the very fine fraction of aerosol poses the most significant health risk, and that much of this fraction is made up of organic compounds. Determining the exact chemical composition of organics in aerosol is extremely difficult since many tens of thousands of compounds are present, varying widely in chemical properties. Speciation is critical however if we are to make direct links between gas phase emissions (for example from petrochemical or natural sources) and aerosol formation and modification. Developing methods to resolve such a complex mixture is an important area of our research producing highly detailed but data intensive characterisations of aerosol composition [See our first desription of more than 10,000 organics in aerosol in Hamilton et al. Atmos. Chem. & Phys. 13, 851-867, 2004, and more on Jacqui Hamilton’s web page]. The image below shows a proportion of a multidimensional GCxGC-TOFMS analysis of sub 400nm particles. Every spot is an individual organic compound - in this portion of the analysis over 3000 components are identified.

image of a proportion of a multidimensional GCxGC-TOFMS analysis of sub 400nm particles

Miniaturised and microfabricated devices

Most observations of chemicals in the environment are made using standard laboratory analytical instrumentation. Whilst these are sensitive and very reliable, they are also often large, heavy and very power hungry. Making observations in remote environments and where mains electricity may not be available requires a different approach. In 2008 we began a new research activity into atmospheric measurements using lab-on-a-chip approaches. This research worked first on developing monolith GC devices, but has expanded to include micro-preparative techniques, organic sensors for indoor and outdoor air, and inorganic sensors for detection of volcanic plumes.

photo of a section of microfabricated GC column
The figure above shows a section of microfabricated GC column, part of a planar field device made from wet etching glass. The column channels are circular - like traditional fused silica - but are laid out on a planar surface such that they may be heated and cooled by thermoelectric devices with high efficiency.