Since October 2008, post-doc at the School of Chemistry, University of Leeds.

PhD in physical chemistry at the University of Oxford (2005).

Post-Doc in the department of physics N.U.I Cork (2006-2008).

DPhil Atmospheric Chemistry

Thesis: Atmospheric interaction of NO₃ with RO₂ at night

 The principal aims of my DPhil research was to study the kinetics of the reactions of NO₃ with peroxy radicals, RO₂, to establish if a relationship between the rate constants and the physical properties of the RO₂ exists, and to assess the impact of the reactions on the night-time chemistry of the troposphere. My research was conducted under the supervision of Professor Richard Wayne, and with the collaboration of Dr Carlos Canosa-Mas, Dr Vasili Kasyutich, and Dr Dudley Shallcross.

I designed and built a reaction system, comprising a discharge–flow tube coupled to CEAS detection systems for NO₃ at λ = 662 nm and NO₂ at λ = 404 nm. This novel use of CEAS allowed the reactions of NO₃ with different RO₂ (CH₃O₂, C₂H₅O₂, CH₂FO₂, CH₂ClO₂, c-C₅H₉O₂, c-C₆H₁₁O₂, CF₃O₂ and CF₃CFO₂CF₃) to be studied in conditions where secondary chemistry was constrained (i.e. [NO₃] < [RO₂]). Rate constants, k, for these reactions were determined to be in the range (0.23 – 3.8) ´ 10⁻¹² cm³ molecule⁻¹ s⁻¹, with only the rate constants for the reactions between the fully-fluorinated peroxy radicals and NO₃ being less than 10⁻¹² cm³ molecule⁻¹ s⁻¹. Calculations of the orbital energies of the reactants, using the Gaussian 03 suite of programs, showed a weak dependence of ln k on the orbital energies of the peroxy species, and it was concluded that the rate constants for the reactions of NO₃ with the majority of RO₂ that are present in the atmosphere are of the order of 10⁻¹² cm³ molecule⁻¹ s⁻¹. A two-box atmospheric model was then used to show that these reactions contribute significantly to the night-time production of OH radicals, compared to a situation where the rate constants were much smaller.

In addition to this primary research, I used a discharge–flow tube coupled to a resonance-fluorescence detection system for Cl to study the kinetics of the reaction of Cl with acetone, using different flow-tube conditions to reduce heterogeneous losses of Cl in the reaction system. Also, I used resonance-fluorescence detection of hydroxy radicals (OH) to investigate the kinetics of the reactions of OH with chlorodimethyl sulphide and compounds that have been suggested as tracers for OH in field experiments, and I developed a relationship between the rate constant for the reactions of OH with substituted aromatics and the energies of the frontier orbitals of the reactants.

Kinetic studies of reactions of Cl atoms with biogenic species of atmospheric importance

A discharge–flow tube, coupled to resonance-fluorescence (RF) detection systems for Cl and I, was employed to quantify the release of atomic iodine in the reaction of Cl with CH₃I. Also, a discharge–flow system, coupled to a multipass absorption cell for detection of NO₃ at λ = 662 nm, was used to study the kinetics of the reaction of NO₃ with 1,4-pentadiene.

2005    Royal Society of Chemistry’s 130^th Faraday Discussions, University of Leeds

Kinetic studies of reactions of the nitrate radical (NO₃) with peroxy radicals (RO₂): an indirect source of OH at night?

2004    International Gas Kinetics Symposium, University of Bristol

            Discharge–flow studies of the reactions of NO₃ with CH₃O₂, C₂H₅O₂ and CF₃O₂.

Apr 2005         Skinner Prize – Best poster at the 130^th Faraday Discussions, University of Leeds.

 

• Kinetic studies of reactions of the nitrate radical (NO₃) with peroxy radicals (RO₂): an indirect source of OH at night? S. Vaughan, C. E. Canosa-Mas, C. Pfrang, D. E. Shallcross, L. Watson, R. P. Wayne, Phys. Chem. Chem. Phys., 8(32), 3749 – 3760, 2006.

• Kinetics of the reaction between OH radicals and chlorodimethylsulphide (CH₃SCH₂Cl). D. E. Shallcross, S. Vaughan, D. R. Trease, C. E. Canosa-Mas, M. V. Ghosh, J. M. Dyke and R. P. Wayne, Atmos. Environ., 40(36), 6899 – 6904, 2006.

• Cavity enhanced absorption: detection of nitrogen dioxide and iodine monoxide using a violet laser diode. V. L. Kasyutich, C. S. E. Bale, C. E. Canosa-Mas, C. Pfrang, S. Vaughan and R. P. Wayne, Appl. Phys. B, 76, 691 – 697, 2003.

•  Off-axis continuous-wave cavity-enhanced absorption spectroscopy of narrow-band and broadband absorbers using red diode lasers. V. L. Kasyutich, C. E. Cansoa-Mas, C. Pfrang, S. Vaughan and R. P. Wayne, Appl. Phys. B, 75, 755 – 761, 2002.

26 November 2008