Atmospheric aerosol particles modify climate by directly scattering or absorbing sunlight and by serving as the seeds for cloud droplets and thereby indirectly scattering sunlight. Atmospheric aerosols also impact human health and ecosystems by contributing significantly to air pollution. On the surface of atmospheric aerosols molecules undergo reactive and photochemical processing, which can change the chemical composition, phase, and structure of the aerosol. These changes can be significant, for instance altering the atmospheric lifetime of pollutants contained within the particles, and changing the toxicity of the aerosol. This processing can also produce volatile molecules that will evaporate into the gas phase, changing atmospheric composition, and the changing nature of the aerosol surface also controls reactive uptake of gases. Although the link between particle and gas phase processing is well-established, there are relatively few investigations that fully resolve the impacts of aerosol photochemical processing in both the particle and gas phases. The kinetic parameters associated with aerosol photochemical processing are poorly quantified which leads to uncertainty in the predictive capability of atmospheric models.
This project is jointly supervised by Professor Dwayne Heard (Leeds) and by Dr Bryan Bzdek (Bristol) and will investigate photochemical processing at aerosol surfaces from two complementary, experimental perspectives:
• At Leeds, an aerosol flow tube equipped with lamps emitting light at actinic tropospheric wavelengths will be used to illuminate submicron aerosols generated from a variety of precursors, with photochemical processing leading to the production or enhanced uptake of gas-phase intermediates, for example OH, HO2 and RO2 radicals, HONO, NO2, and volatile organic compounds (in particular oxygenated species), which will be quantified.
• At Bristol, experiments on individual trapped droplets will complement the ensemble aerosol flow tube experiments at Leeds, allowing detailed investigation of the changes to droplet chemical and physical properties arising from photochemical processing.
Combined, the gas and particle phase studies will permit development of a kinetic model that quantitatively describes the chemical pathways occurring within the bulk and at the surface of the aerosol. Of particular interest are the role of photo-sensitizers and other light absorbing substances, for example those present in aerosols derived from humic acid (a component of soil) and brown carbon aerosols. The model will also describe the resulting modifications to key aerosol properties including size, viscosity, and surface composition, and the impact on the surrounding gas phase composition.
This project is part of the EPSRC Centre for Doctoral Training in Aerosol Science - more details, including how to apply, can be found here: https://www.aerosol-cdt.ac.uk/
UK/EU – Paying academic fees of £4,600 for Session 2020/21, together with a maintenance grant (currently £15,009 in Session 2019/20) paid for 4 years.
UK applicants will be eligible for a full award paying tuition fees and maintenance. European Union applicants will be eligible for an award paying tuition fees only, except in exceptional circumstances, or where residency has been established for more than 3 years prior to the start of the course. Funding is awarded on a competitive basis.