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Kinetics and Atmospheric Impacts of Criegee Intermediate Reactions with Peroxy Radicals

Dr Daniel Stone (SoC), Dr Mark Blitz (SoC), Prof Paul Seakins (SoC)

Contact email: d.stone@leeds.ac.uk

Volatile organic compounds (VOCs), emitted from both anthropogenic and biogenic sources, are oxidised in the atmosphere, leading to complex reaction cascades and production of highly reactive trace species (Johnson and Marston, 2008; Stone et al., 2012). This chemistry is responsible for the removal of primary pollutants from the atmosphere and for the production of secondary pollutants including ozone and secondary organic aerosol, and is consequently central to air quality and climate. Policies designed to address such issues are reliant on a fundamental understanding of the chemistry controlling atmospheric composition. 

For saturated VOCs, oxidation is often initiated by reaction with the OH radical, generating peroxy radicals (RO2), while for unsaturated VOCs there are additional oxidation mechanisms initiated by reaction with ozone which lead to formation of Criegee intermediates (R2COO) (Johnson and Marston, 2008).

Figure 1: Molecular structures of peroxy radicals (right) and Criegee intermediates (left).

Developments in laboratory studies of Criegee intermediate chemistry within the last few years have led to a number of discoveries regarding the role of Criegees in the atmosphere, including work by this group (Stone et al., 2013; Stone et al., 2014, Lewis et al., 2015), and have highlighted several unexpected and important atmospheric impacts. Recent work has shown the potential for reactions between Criegee intermediates and peroxy radicals, offering explanations that link gas phase chemistry with the first steps in the formation of secondary organic aerosol (SOA) (Vereecken et al., 2012; Anglada et al., 2013; Bonn et al., 2014; Zhao et al., 2015; Ahmad et al., 2017). However, detailed examination of the kinetics of reactions between Criegee intermediates and peroxy radicals has yet to be performed, and is critical to the assessment of the role of these reactions in secondary aerosol formation and thus on air quality and climate.

Objectives

In this project you will take advantage of new opportunities to investigate the chemistry and impacts of Criegee intermediates in the atmosphere, with a particular focus on their reactions with peroxy radicals.  You will use laser flash photolysis combined with novel time-resolved multipass broadband UV spectroscopy techniques recently developed in Leeds (Lewis et al., 2015) to monitor Criegee intermediates and peroxy radicals directly, in real-time, to determine their reaction kinetics. You will also be involved in the development of novel instrumentation using quantum cascade lasers (QCLs) to make direct observations reaction products by time-resolved infrared spectroscopy in order to determine product yields at temperatures and pressures relevant to the atmosphere. According to your particular research interests, the studentship could involve:

  • Laser flash photolysis coupled with time-resolved broadband UV spectroscopy to monitor Criegee intermediates and peroxy radicals in real-time throughout their reactions to determine reaction kinetics.
  • Development of novel instrumentation using quantum cascade lasers to monitor reaction products via infrared spectroscopy in real-time throughout a reaction.
  • Further instrument development to enable monitoring of Criegee intermediates and peroxy radicals in complex reaction systems in an atmospheric chamber.
  • Modelling of experimental results to assess atmospheric impacts.
  • Application of experimental techniques to combustion chemistry and other areas of atmospheric relevance.

Figure 2: Schematic of experimental apparatus for time-resolved broadband UV absorption measurements of Criegee intermediates and peroxy radicals.

Figure 3: Schematic of experimental apparatus for infrared absorption measurements of Criegee intermediates and reaction products.

Potential for high impact outcome

The role of chemistry in controlling atmospheric composition is of fundamental importance to our understanding of air quality and climate change.  This work will lead to improved understanding of the chemistry and impacts of Criegee intermediates in the atmosphere, providing greater constraints on model calculations of global oxidising capacity and production of secondary organic aerosol. Criegee chemistry has been the subject of a number of high impact papers in Science and Nature in recent years (Welz et al., 2012; Mauldin et al., 2012; Taatjes et al., 2013; Su et al., 2013). It is anticipated that this project will generate several papers, with potential for publication in high impact journals.

Training

The student will work under the supervision of Dr Daniel Stone, Dr Mark Blitz and Prof Paul Seakins within the atmospheric and physical chemistry group in the School of Chemistry in Leeds. You will be supported by a range of supervisions from monthly meetings and group presentations, through to daily informal chats with supervisors. You will work in well-equipped laboratories and be part of an active, thriving and well-funded atmospheric chemistry community. The Leeds and York groups receive funding from the National Centre for Atmospheric Science (NCAS) and are part of the Atmospheric Measurement Facility, and have an internationally leading reputation in atmospheric chemistry for field measurements of atmospheric composition, laboratory studies of chemical kinetics and photochemistry, and the development of numerical models and chemical mechanisms, including the Master Chemical Mechanism (MCM). Activities in these three areas are intimately linked and interdependent, providing a significant advantage. You will be supported to attend both national and international conferences, and will receive a wide range of training, for example in communication skills, project management, and with other technical aspects (for example Labview and computing). The PhD will provide a broad spectrum of experience in the use of high power lasers, vacuum systems, optics, computer controlled data acquisition systems and methods in numerical calculations. The successful PhD student will have access to a broad spectrum of training workshops that include an extensive range of training workshops in numerical modelling, through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).

Student profile

The student should have an interest in atmospheric chemistry, air quality and global environmental problems, with a strong background in experimental physical chemistry or similar (e.g. physics, engineering, environmental science).

References

  • W. Ahmad et al., J. Aero. Sci., 2017, 110, 70-83
  • J. M. Anglada et al., Phys. Chem. Chem. Phys., 2013, 15, 18921-18933
  • B. Bonn et al., Atmos. Chem. Phys., 2014, 14, 10823-10843
  • D. Johnson & G. Marston, Chem. Soc. Rev., 2008, 37, 699-716
  • T. Lewis et al., Phys. Chem. Chem. Phys., 2015, 17, 4859-4863
  • R.L. Mauldin et al., Nature, 2012, 488, 193-197
  • D. Stone et al., Chem. Soc. Rev., 2012, 41, 6348-6404
  • D. Stone et al., Phys. Chem. Chem. Phys., 2013, 15, 19119-19124
  • D. Stone et al., Phys. Chem. Chem. Phys., 2014, 16, 1139-1149
  • Y.T. Su, Science, 2013, 340, 174-176
  • C.A. Taatjes et al., Science, 2013, 340, 177-180
  • L. Vereecken et al., Phys. Chem. Chem. Phys., 2012, 14, 14682-14695
  • O. Welz et al., Science, 2012, 335, 204-207
  • Y. Zhao et al., Phys. Chem. Chem. Phys., 2015, 17, 12500-12514

Related undergraduate subjects:

  • Atmospheric science
  • Chemistry
  • Environmental science
  • Natural sciences
  • Physical science
  • Physics