2027-B08 Less emission, more aerosol? How elevated CO2 changes organic gas emissions from forests and their capacity to form particles
PROJECT HIGHLIGHTS
- Measure the emissions of a future forest directly, at the world-leading BIFoR free-air CO2 enrichment (FACE) experiment
- Laboratory and modelling work to find out which compounds control atmospheric particle formation from real forest mixtures
- International training with the ACE-Forest Centre of Excellence at the University of Eastern Finland, plus hands-on training on several research mass spectrometers
Overview
Forests emit large amounts of volatile organic compounds (VOCs). In the atmosphere these are oxidised to form large, oxygenated gases which then form secondary organic aerosol (SOA): tiny particles that scatter sunlight and form cloud droplets. The effect of aerosol on clouds is the largest single source of uncertainty in how much humans have changed the climate. Forest emissions therefore feed back on climate, but we do not know how this feedback will change as atmospheric CO2 rises.
Trees respond to high CO2 by changing both how much they emit and what they emit. Isoprene is the most abundant VOC emitted by plants, and its emission from many species, including oak, falls under elevated CO₂, while monoterpene and sesquiterpene responses are more variable. These compounds differ enormously in how well they make particles. Isoprene makes little SOA itself, and it actively suppresses particle formation from monoterpenes by interfering with the chemistry that builds oxygenated gases. A forest that emits less isoprene but similar or more monoterpene could therefore make more aerosol, even though its total emissions have fallen (Figure 1).
This project will test that idea in a real forest. The Birmingham Institute of Forest Research (BIFoR) FACE facility has exposed a mature oak woodland to CO2 150 ppm above ambient since 2017, alongside control plots at current CO2. It is one of very few places in the world where the emissions of a future forest can be measured directly.
The doctoral researcher (DR) will measure the VOC mixtures emitted under current and elevated CO₂, recreate those mixtures in the laboratory to measure how much aerosol they form, and use a chemical box model to work out which compounds cause any difference. Part of the laboratory work will take place at the University of Eastern Finland (UEF) with Dr Angela Buchholz, within the ACE-Forest Centre of Excellence, a leading group in aerosol formation from real plant emissions.
The outcome will be the first direct, mechanistic estimate of how CO2 fertilisation changes the aerosol-forming potential of a mature temperate forest, something climate models currently have to assume.
Figure 1: The hypothesis. (left) Today, trees emit gases which form aerosol particles, which influence the climate. (right) under elevated CO₂, this mixture of emissions may be different in a way that forms more, or less particles.
Case Projects
This project does not offer a CASE studentship
Host
University of Birmingham
Theme
Climate and Environmental Sustainability, Organisms and Ecosystems
Supervisors
Project investigator
- Dr James Brean, j.brean@bham.ac.uk
Co-investigators
- Dr Angela Buchholz, University of Eastern Finland (Department of Technical Physics, Kuopio), angela.buchholz@uef.fi
How to apply
Each host has a slightly different application process.
Find out how to apply for this studentship.
All applications must include the CENTA application form.
Methodology
Field: the DR will sample VOCs onto Tenax sorbent tubes at leaf, branch and canopy level in the forest with elevated and regular CO2 across the growing season, and analyse them by comprehensive two-dimensional gas chromatography mass spectrometry (GCxGC-ToF-MS) at Birmingham. An intensive campaign with a deployable GC-EI-ToF-MS on loan from the University of East Anglia will capture the diurnal cycle of emissions under each treatment.
Laboratory: measured mixtures will be recreated and oxidised in flow tube reactors at UEF, measuring SOA yield (particle sizers, aerosol mass spectrometry), highly oxygenated molecules (nitrate CIMS) and particle volatility (FIGAERO-CIMS).
Modelling: an explicit chemical box model constrained by these data will be run with individual compounds switched in and out, isolating which changes in the mixture drive the difference in SOA.
Further details and How to Apply
For informal enquiries please contact Dr James Brean (j.brean@bham.ac.uk).
To apply to this project:
- You must include a CENTA studentship application form, downloadable from: CENTA Studentship Application Form 2027
- You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities.
- Please submit your application and complete the host institution application process via: https://admissions.bham.ac.uk/course-finder-landing-page/?code=LES068 Please select the PhD in Geography (CENTA) 2027 entry year Apply Now button. The CENTA Studentship Application Form 2027 and CV can both be uploaded to the Personal Statement section of the online form. In the funding section of the online form please select Research Council Funding and then choose Natural Environment Research Council (NERC). Please quote CENTA 2027-B08 when completing the application form.
Applications must be submitted by 23:59 GMT on Wednesday 6th January 2027.
