Atmospheric Chemistry of Multi-functional Compounds

The atmospheric photochemistry of hydrocarbons plays important roles in issues such as photochemical smog formation (with links to air quality and health) and to aerosol formation (with links to air quality, health and climate). Whilst there have been many studies on the atmospheric oxidation of important simple species such as isoprene (a key biogenic emission) or aromatics (important anthropogenic emissions), much less is known about the chemistry of multifunctional species which are the focus of this project.

The first step in the oxidation process is the reaction of a radical, usually OH, with the organic compound to generate a radical species. A simple example would be the reaction of OH with propane, CH3CH2CH3. Abstraction at the CH3 group will lead to the production of an aldehyde, propanal; abstraction at the CH2 group leads to a ketone, acetone, being formed. Aldehydes and ketones have different atmospheric impacts (reactivities, absorption cross sections, toxicities) so knowing the site at which the reaction takes place to crucial to the subsequent chemistry.

Structure activity relationships (SAR) are based on experimental data and can be used to predict abstraction sites for compounds where experimental data are lacking. SARs have been developed for a number of simple compounds, e.g. alkanes and alcohols.1 Well validated SAR do not exist for multifunctional species.

An important example of a multifunctional species would be monoethanolamine (MEA) which contains both OH and NH2 functional groups and proposed as an important material in Carbon Capture and Storage (CCS, this is highly topical considering the recent UK Government announcement on greening of energy production). How do these two functional groups interact to determine the overall reactivity of this species? For MEA there have been some studies at Leeds2 that start to answer these questions, but for most multifunctional species, whether they be primary emissions such as MEA, or formed in the atmosphere from the oxidation of simpler species, no information is available.

Given the huge number of multifunctional species, an experimental determination of each compound is unfeasible; we need to combine experimental effort with an accurate predictive capability. Structure Activity Relationships (SAR) are currently used to predict reaction rates, but reliable SAR for multifunctional species do not exist.

There are several strands to this project which will allow you to develop a range of skills:

  1. The generation of a range of test-bed data on the reactions of OH with a range of multifunctional compounds. You would use a range of experimental methods including studies based around laser methods3 and also using the HIRAC simulation chamber.
  2. Construction of SAR for important multifunctional species based on your own measurements and literature surveys.
  3. Testing SAR predictions against measured OH rate coefficients and site specific data obtained from chamber measurements.
  4. Assessing the impact of your experimental data and SAR on important systems. Inputting new or revised site specific rate coefficients into comprehensive models such as the Master Chemical Mechanism (MCM), will allow you to assess the impact of your results and compare with real observations (e.g. satellite measurements).

Skills, Opportunities, Support

As part of the project you should gain a wide range of skills across a range of experimental techniques (e.g. FTIR, mass spectroscopy, laser spectroscopy) and into various aspects of modelling. These skills should allow you to access opportunities in further research (academic or commercial) or in industry.

As well as working with a wide range of techniques and approaches here at Leeds, there would be opportunities to interact with other experimental and modelling groups for example in York and Edinburgh. Work in this project links to current NERC grants: UNFOGS (Understanding Formaldehyde and Glyoxal Chemistry for Satellite measurements) and PEROXY (Peroxy Radical Chemistry) where the supervisory team are either the lead investigators or co-investigators.

PhD students and researchers from UNFOGS and PEROXY will be available to provide day-to-day support and you will be part of an active research group with regular group meetings and opportunities for internal presentations to both the group and wider audiences. Students and researchers in the groups are actively encouraged to present their work at international conferences such as AGU, EGU and ACM.

References

  1. Bethel, H. L.; Atkinson, R.; Arey, J., Kinetics and products of the reactions of selected diols with the OH radical. Int. J. Chem. Kinet. 2001, 33 (5), 310-316.
  2. Onel, L.; Blitz, M. A.; Breen, J.; Rickardcd, A. R.; Seakins, P. W., Branching ratios for the reactions of OH with ethanol amines used in carbon capture and the potential impact on carcinogen formation in the emission plume from a carbon capture plant. PCCP 2015, 17 (38), 25342-25353.
  3. Glowacki, D. R.; Lockhart, J.; Blitz, M. A.; Klippenstein, S. J.; Pilling, M. J.; Robertson, S. H.; Seakins, P. W., Interception of excited vibrational quantum states by O2 in atmospheric association reactions. Science 2012, 337 (6098), 1066-1069.