Atmospheric chemical processing determines the link between emissions to the air and atmospheric composition, which in turn affects climate and health. The biosphere is the largest source of organic compounds to the atmosphere, with trees dominating production of biogenic volatile organic compounds (BVOCs) such as isoprene and monoterpenes. VOCs go on to form ozone (harmful to human health, crop yields and ecosystems) and fine particles (again, harmful to health, and impacting climate through scattering of radiation and influencing cloud formation).
However, the totality of BVOC emissions is poorly understood. Many thousands of species are formed and attempts to characterise them individually face large gaps: bottom-up estimates indicate differences of up to 50% between individually measured species and the total concentration known to be present! This matters because BVOC loading determines the pool of reactive organic material available to form atmospheric particles. In addition, oxidation cycles are initiated by reagents such as OH, where alkene ozonolysis is a major source of OH and ozone sinks. Key questions include: What is the total BVOC population present in key environments? What is the contribution of alkene-ozone reactions to OH formation and subsequent particle formation?
This student will work with an improved design of the unique University of Birmingham Total Ozone Reactivity System (TORS), refining recent upgrades to allow us to vary the reaction time in a controlled and reproducible way, allowing ozone decay to be measured across a well-defined kinetic window. Experiments with selected BVOCs will determine reaction rates and establish how instrument conditions affect sensitivity and precision. Where feasible, mass spectrometry (PTR-MS) measurements will track selected gas-phase products, providing constraints on product formation while recognising the limitations of mass-spectrometric isomer identification. The measurements will be interpreted using an established atmospheric model, the Master Chemical Mechanism (MCM). Box-model simulations and sensitivity analysis will test the consistency of proposed chemistry, identify influential product channels and quantify how revised kinetics affect predicted ozone loss, radical production and downstream oxidation. By connecting precision laboratory kinetics with mechanism evaluation, the project will deliver fundamental data needed for more reliable predictions of atmospheric composition.
This project does not offer a CASE studentship
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The project combines flow-reactor kinetics, trace-gas analysis and atmospheric modelling, following on from earlier studies at the BIFoR FACE facility which started identifying key BVOCs relevant in ambient and elevated CO2 forested environments. The student will refine TORS around a movable injection point, then characterise residence time, mixing, wall losses, and detection limits. For selected unsaturated BVOCs, pseudo-first-order experiments will measure ozone decay across multiple reaction times and concentrations, yielding bimolecular rate coefficients. PTR-MS will monitor reactants and selected volatile products where signals can be assigned and calibrated, with complementary standards or literature constraints used where required. MCM box modelling will simulate experiments, comparing measured and predicted time profiles. The resulting rate coefficients and product constraints will then be tested under representative atmospheric conditions to determine their influence on further secondary chemistry.
DRs will be awarded CENTA Training Credits (CTCs) for participation in CENTA-provided and ‘free choice’ external training. One CTC can be earned per 3 hours training, and DRs must accrue 100 CTCs across the three and a half years of their PhD.
During this PhD you will develop an integrated experimental and computational skillset. Training will cover flow-reactor design, vacuum and gas-handling systems, instrument automation, ozone measurements and PTR-MS, alongside safe handling of trace gases. You will learn kinetic experimental design, calibration, uncertainty analysis and reproducible data processing in Python. Training in the Master Chemical Mechanism and atmospheric box modelling will connect laboratory observations to environmental consequences. You will also develop transferable skills in project management, scientific writing, presentations, teamwork, data management and public engagement through CENTA training, seminars, workshops and conferences.
Year 1: Rebuild and characterise the sliding-injection TORS; establish residence times, mixing, wall-loss corrections, calibration procedures and benchmark kinetics.
Year 2: Measure ozone + BVOC rate coefficients across selected compounds and conditions; introduce PTR-MS measurements of reactants and selected products.
Year 3: Complete priority kinetics and product studies; integrate results into MCM box models, quantify atmospheric impacts, and prepare publications and the thesis.
Sommariva, R., et al., (2020) ‘An instrument for in situ measurement of total ozone reactivity’, Atmospheric Measurement Techniques, 13, pp.1655-1670. doi: 10.5194/amt-13-1655-2020
Atkinson, R. and Arey, J. (2003) ‘Atmospheric degradation of volatile organic compounds’, Chemical Reviews, 103, pp. 4605–4638. doi: 10.1021/cr0206420.
Bloss, C. et al. (2005) ‘Development of a detailed chemical mechanism (MCMv3.1) for the atmospheric oxidation of aromatic hydrocarbons’, Atmospheric Chemistry and Physics, 5, pp. 641–664. doi: 10.5194/acp-5-641-2005.
He, X. et al. (2026) ‘Tree selection in urban greening shapes air quality for global cities’, Science Advances, 12, pp. eaee5583. doi:10.1126/sciadv.aee5583
Project contact details: Dr Julia Lehman, [email protected].
To apply to this project:
Applications must be submitted by 23:59 GMT on Wednesday 6th January 2027.