School of Earth and Environment

Climate and Atmospheric Science (ICAS) PhD Projects

Halogens in the Lower Atmosphere

Supervisor: Professor Martyn Chipperfield

The halogen family of chemical species (i.e. chlorine, bromine and iodine) play very important roles in the chemistry of the stratosphere and troposphere. Over the past few decades the use of compounds such as chlorofluorocarbons (CFCs) has led to a large increase in the amount of chlorine in the stratosphere. Once released from the CFCs, chlorine can destroy stratospheric ozone and this leads to the Antarctic Ozone Hole every springtime. Through the Montreal Protocol, the production/emission of CFCs and similar long-lived gases is now controlled and stratospheric chlorine levels are decreasing. The stratospheric ozone layer should recover on a timescale of the next 50 years.

However, other factors will affect the recovery of stratospheric ozone. Bromine is about 50x more efficient at destroying stratospheric ozone than chlorine. Moreover, it is now known that about 25% of the bromine reaching the stratosphere comes from short-lived natural compounds (e.g. bromoform, dibromomethane). There is currently a great deal of uncertainty in the strength of these natural sources and how short-lived compounds reach the stratosphere (e.g. Hossaini et al., 2010). A field campaign as part of the European Union SHIVA project is planned in late 2011 in Malaysia to obtain more data on this.

Halogens also play a key role in the troposphere. Bromine is an important oxidant for dimethylsulfide (DMS), which affects aerosol/cloud formation and therefore climate (see Breider et al., 2010). Iodine is also believed to impact on the tropospheric ozone budget and recent studies suggest that tropospheric chlorine chemistry, which has so far been essentially ignored, might be important.

This modeling PhD project will build on a lot of our group’s work over the past few years (see reference list for example papers). The project will use state of the art three-dimensional models (TOMCAT/SLIMCAT and a Chemistry-Climate Model) to study combined troposphere/stratosphere halogen chemistry. A particular new focus will be on tropospheric iodine/chlorine chemistry. Depending on the start date, there could be the possibility to participate in the EU SHIVA campaign.

Applicants should have a good BSc degree in a quantitative physical science, computing, engineering or mathematics. Applications from Masters students are also welcome.

References

  • Breider, T., M. P. Chipperfield, N.A.D. Richards, K.S. Carslaw, G.W. Mann, and D.V. Spracklen, The impact of BrO on dimethylsulfide in the remote marine boundary layer, Geophys. Res. Lett., 37, L02807, doi:10.1029/2009GL040868, 2010.
  • Hossaini, R., M.P. Chipperfield, B.M. Monge-Sanz, N.A.D. Richards, E. Atlas, D.R. Blake, Bromoform and Dibromomethane in the Tropics: A 3D Model Study of Chemistry and Transport, Atmos. Chem. Phys., 10, 719-735, 2010.
  • Butz, A., H. Bösch, C. Camy-Peyret, M.P. Chipperfield, M. Dorf, S. Kreycy, L. Kritten, C. Prados-Román, J. Schwärzle, and K. Pfeilsticker, Constraints on inorganic gaseous iodine in the tropical upper troposphere and stratosphere inferred from balloon-borne solar occultation observations Atmos. Chem. Phys., 9, 7229-7242, 2009.
  • Sinnhuber BM, Sheode N, Sinnhuber M, Chipperfield MP, Feng W The contribution of anthropogenic bromine emissions to past stratospheric ozone trends: a modelling study Atmos. Chem. Phys., 9, 2863-2871, 2009.
  • Dorf, M., A. Butz, C. Camy-Peyret, M. P. Chipperfield, L. Kritten, and K. Pfeilsticker Bromine in the tropical troposphere and stratosphere as derived from balloon-borne BrO observations Atmos. Chem. Phys., 8, 7265-7271, 2008.
  • Kovalenko, L.J., NL Livesey, RJ Salawitch, C Camy-Peyret, MP Chipperfield, et al., Validation of Aura Microwave Limb Sounder BrO observations in the stratosphere, J. Geophys. Res., 112, D24S41, doi:10.1029/2007JD008817, 2007.