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NERC E4 Plant canopies as chemical reactors


School of Chemistry

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Prof Mathew Heal , Dr E Nemitz , Dr Massimo Vieno , Prof David Simpson No more applications being accepted Competition Funded PhD Project (Students Worldwide)

About the Project

Atmospheric chemistry controls the fate of many pollutants emitted to the air and their impact on human health and ecosystems. Chemistry produces particulate matter, PM2.5, nitrogen dioxide (NO2) and ozone (O3). These compounds dominate the impact of air pollution on human health, whilst the deposition of O3 also reduces crop yields and that of nitrogen compounds reduces biodiversity. Plants do not only suffer from air pollution; they also contribute to it by emitting a range of volatile organic compounds (VOCs).

Chemistry not only occurs in the free atmosphere, but also within plant canopies, where it is driven by strong disequilibrium conditions induced by steep gradients in concentrations and meteorological parameters (sunlight, temperature and humidity). This in-canopy chemistry contributes to atmospheric chemistry overall and modulates the effective pollutant removal of the canopy and also the pollutant doses experienced by the plants. These processes are not resolved by the atmospheric chemistry and transport models (ACTMs) used to predict air quality, climate change and their impacts. This project will develop and apply a 1-dimensional coupled model of transport, plant-atmosphere exchange and chemistry to study the processes and their importance at a number of forest sites for which comprehensive measurements of above and in-canopy concentrations and fluxes exist. It will assess the importance of quantifying in-canopy chemistry for pollutant deposition and the composition of the atmosphere, and then derive simplified representations for use in ACTMs for upscaling. The student will have the opportunity to get involved in field measurement campaigns.

Key research questions
• To what extent is vegetation / atmosphere exchange of reactive gases (NOx, NH3, HNO3, VOC) and aerosol components (e.g. NH4NO3) modified by in-canopy chemical processes?
• How does the importance of in-canopy chemistry change between ecosystems, and with chemical and meteorological climate?
• Do flux measurements made above plant canopies need to be corrected for chemical loss / production inside the canopy in order to derive the true vegetation exchange?
• Can the mechanistic fully-coupled 1D model be simplified to be computationally efficient while still adequately reproducing the effect?

Methodology
A 1-dimensionsal modelling framework (ESX) has recently been developed for the simulation of the coupled pro­cesses of plant exchange, vertical transport and chemistry. This modular and scalable model is intended to become a depository of the state-of-the-art of surface / atmosphere modelling, from which simplified modules for the application in 3-dimensional transport models can be derived. It is designed to interface with the EMEP ACTM, which underpins European air pollution policy. This studentship will use and further develop the offline version of the model (a) to assimilate existing flux measurements of single species to derive ESX-compatible parameterisations of the exchange process and (b) to assess its chemical predictions against existing comprehensive datasets of concentration and fluxes of interacting species from temperate and tropical forests. It will then use the model to quantify the effect of in-canopy chemistry, initially at individual measurement sites and then more generally, by coupling the ESX model or a simplification thereof to the EMEP ACTM.

Training
A comprehensive training programme will be provided comprising specialist scientific training and generic transferable and professional skills. This includes a programme focused on personal effectiveness, communication, and career and project management, literature searching, presentations, and thesis writing. The student will receive training in undergraduate laboratory demonstrating and project supervision and have the opportunity to attend relevant atmospheric science courses available in the UoE. The student will attend appropriate summer schools (e.g. NCAS Climate Modelling Summer School, Intensive Course “First Steps in Biosphere-Atmosphere Modelling”, Lund, Sweden). They will have the opportunity to become involved in UKCEH’s field measurement programme to develop an understanding of the origin of the data they work with as well as their limitations.

Qualifications and eligibility
This studentship would suit someone with a degree in chemistry, physics, environmental science, meteorology or a related discipline who is highly numerate with experience in computer programming (ideally Fortran and/or Python under LINUX). Knowledge of atmospheric physics, chemistry and/or numerical modelling would be an additional benefit.

Applications must be made to the E4 DTP www.ed.ac.uk/e4-dtp/how-to-apply . Prior informal enquiries to the supervisors are welcome.

Equality & Diversity statement
The School of Chemistry holds a Silver Athena SWAN award in recognition of our commitment to advance gender equality in higher education. The University is a member of the Race Equality Charter and is a Stonewall Scotland Diversity Champion, actively promoting LGBT equality. The University has a range of initiatives to support a family friendly working environment. https://www.ed.ac.uk/equality-diversity/help-advice/family-friendly


Funding Notes

A 3.5 year PhD studentship funded through the NERC Edinburgh Earth, Ecology and Environment (E4) Doctoral Training Partnership (www.ed.ac.uk/e4-dtp).

References

Nemitz, E. and Sutton, M.A., Gas-particle conversions above a Dutch heathland: III. Modelling of size-dependent NH4+ fluxes as modified by the NH3-HNO3-NH4NO3 equilibrium, Atmos. Chem. Phys. 4, 1025-1045, 2004.
Ganzeveld, L. N., Lelieveld, J., Dentener, F. J., Krol, M. C., Bouwman, A.J. and Roelofs, G.-J. Global soil-biogenic NOx emissions and the role of canopy processes, J. Geophys. Res., 107(D16), doi:10.1029/2001JD001289, 2002.
Ashworth, K., Chung, S. H., Griffin, R. J., Chen, J., Forkel, R., Bryan, A. M., and Steiner, A. L.: Forest canopy atmosphere transfer (forcast) 1.0: A 1-d model of biosphere–atmosphere chemical exchange, Geosci. Model Dev., 8, 3765-3784, doi: 10.5194/gmd-8-3765-2015, 2015.
Zhou, P., Ganzeveld, L., Rannik, Ü., Zhou, L., Gierens, R., Taipale, D., Mammarella, I., and Boy, M.: Simulating ozone dry deposition at a boreal forest with a multi-layer canopy deposition model, Atmos. Chem. Phys., 17, 1361-1379, doi:10.5194/acp-17-1361-2017, 2017
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