Professor Alastair Lewis

Phone: 01904 322522

Atmospheric Chemistry

Alastair Lewis was appointed as professor of atmospheric chemistry at the University of York in 2006 working within the Wolfson Atmospheric Chemistry Laboratories. In addition to teaching and research at the University, Alastair is currently Deputy Director of, and Director for atmospheric composition, at the National Centre for Atmospheric Science (NCAS).


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. Natural emissions are often even less well understood; some VOCs are released from vegetation, others by biomass burning or from the oceans. We recently established, for example, the global impacts of benzene released from forest firesOur 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 resolution methods of analysis we showed how complex urban air can be. 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 traceability 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 makes 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, the image below shows a proportion of a multidimensional GCxGC-TOFMS analysis of sub 400nm particles where 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

Career Summary

Previous to his appointment as professor, Alastair 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 has more than 230 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 been Principle Investigator on three major NERC consortium experimental atmospheric chemistry projects, TORCH, ITOP and AIRPRO, the latter being part of a major international collaboration studying air pollution in Beijing.  Alastair is a member of a number of expert advisory groups including for Defra, the World Meteorological Organisation and UNEP. He was a member of the last REF-2014 sub-panel 8 (Chemistry).

Current research activities include reactive air pollution in the atmosphere and its contribution to urban and global air pollution, indoor air quality, 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 government on air pollution policy, and is a member of the Defra Air Quality Expert Group, and has provided evidence to House of Commons select committees on this subject. He also works with industry translating atmospheric chemical technologies into other fields. Recent collaborations include joint research projects with Markes International, the National Physical Laboratory, DSTL, Givaudan UK, Anatune Ltd and AWE plc.


Selected publications (for a full list see the York Research database link in the right-hand column)

  • Validate Personal Air Pollution Sensors. A.C Lewis and Edwards P.M. Nature, 535, 29-31, 2016. DOI: 10.1038/535029a 
  • A Reversal Of Global Atmospheric Ethane And Propane Trends Largely Due To US Oil And Gas Production. D. Helmig, S Rossabi, J Hueber, P Tans, S Montzka, K Masarie, K Thoning, C Plass-Duelmer, A.C Lewis, L.J Carpenter, S Punjabi, S Reimann, M. Vollmer, R Steinbrecher, J Hannigan, L Emmons, E Mahieu, B Franco, D Smale & A Pozzer. Nature Geoscience. 9, 490-495, 2016. DOI:10.1038/ngeo2721 
  • Evidence for a recent decline in European vehicular NO2. S.K Grange, S.M Moller, A.C Lewis, and D.C Carslaw. Nature Geoscience, 10, 2017, 914-918. DOI: 10.1038/s41561-017-0009-0 
  • The Changing Face Of Urban Air Pollution. A.C Lewis. Science, 359, 744-745, 2018.  DOI: 10.1126/science.aar4925
  • Discrepancy Between Simulated And Observed Ethane And Propane Levels Explained By Underestimated Fossil Emissions. S.B Dalsøren, Myhre, Ø Hodnebrog, C Lund Myhre, A Stohl, I Pisso, S Schwietzke, L Höglund-Isaksson, D Helmig, S Reimann, S Sauvage, N Schmidbauer, K.A Read, L.J Carpenter, A.C Lewis, S Punjabi, and M Wallasch.Nature Geoscience, 11, 178-184, 2018. DOI:10.1038/s41561-018-0073-0

Awards and Activities

Awards and Prizes

  • Desty Memorial Prize for ‘Innovation in Separation Science’ (2001)
  • Philip Leverhulme Prize in ‘Earth Ocean and Atmospheric Sciences’ (2004)
  • Royal Society of Chemistry ‘SAC Silver Medal’. (2006)
  • Royal Society of Chemistry ‘John Jeyes Award’ (2012)

Research activities/funding

  • £25M in research funding from NERC, EPSRC, EU, MOD, Defra since 2001.
  • Industrial collaboration with more than 15 companies on chemical detection technologies.
  • Principal Investigator for NERC community consortium projects: TORCH (Tropospheric organic Chemistry Experiment), ITOP (Intercontinental Transport of Ozone and Precursors), AIRPRO (Air Pollution Processes in Beijing)
  • Around 230 published articles, including 10 book chapters and the Wiley reference book 'Multidimensional Chromatography'

Professional activities

  • Theme Leader for Technologies, Natural Environment Research Council (2007-2013)
  • Director for Atmospheric Composition, National Centre for Atmospheric Science (NCAS) (2007-present)
  • Science Advisory Group, Reactive Gases, World Meteorological Organisation (2009- 2016)
  • Science Advisory Panel, UNEP GEO-6 (2015-present)
  • STFC Futures Programme Advisory Board (2011-2014)
  • NERC Joint Capital Advisory Group (2014-2017)
  • Defra Air Quality Expert Group (2012-present)
  • HEFCE Research Excellence Framework (REF2014) sub-panel 8 (chemistry) member (2011-2014)
  • Advisory Board, Analytical Methods
  • Fellow of the Royal Society of Chemistry
  • IGAC, International Global Atmospheric Chemistry, Science Steering Committee (2015-2018).