Suppression of air pollution via aerosol mediated removal of peroxy radicals
Project Description
Air quality is an acute societal concern with around 7 million people dying per year from the combined effect of outdoor and indoor air pollution (World Meteorological Organization). Ozone (O3) is a harmful pollutant, as well as an important greenhouse gas, and this project is associated with the discovery of a new “aerosol inhibited” photochemical O3 regime (Ivatt et al., 2022). For the last 30 years, air quality policy for reducing O3 pollution has split the world into NOx or VOC (volatile organic carbon) limited regimes based on the dominant free radical (ROx) chain termination step. Depending on the regime, policymakers have either reduced NOx or VOC emissions to reduce O3. This has led to substantial reduction in O3 concentrations over Europe and North America. For some parts of the world the dominant chain termination reaction is not one of the standard routes, but rather the reactive removal of the peroxy radical HO2 onto aerosol surfaces, placing these regions into the new “aerosol inhibited” photochemical regime (Ivatt et al., 2022). There is a strong interaction and hence tension between policies to reduce particulate matter (PM, also damaging to health) and O3. Efforts to reduce PM (aerosol) levels would lead to the unintended consequence of increasing O3 concentration (as might have been seen recently in China, Li et al., 2020). The rates of uptake onto aerosols of HO2, and also of organic peroxy radicals, are poorly constrained, and a much better understanding of this ozone regime is necessary to drive the best policy.
In this project a new field instrument for the direct measurement of the rate of removal of peroxy radicals onto atmospheric aerosols will be developed. It will be deployed alongside our existing field instrumentation for the measurements of free-radicals (shown in Figure 1) to provide a unique capability to understand the real world uptake of radicals onto aerosol. The new measurements will be included in models to further understanding O3 regimes important for air quality and climate.
Figure 1. The Leeds FAGE instrumented shipping container for the measurement of radicals deployed during fieldwork at the Cape Verde Atmospheric Observatory. FAGE is part of AMOF (Atmospheric Measurement & Observation Facility) which is a component of NCAS (the National Centre for Atmospheric Science).
Project Objectives
The project is a combination of fieldwork, laboratory studies and numerical modelling, and will have the following specific objectives:
(1) To develop a new field instrument to measure the rate of loss of HO2 and some RO2 onto ambient aerosol
(2) To deploy this instrument at the NERC Air Pollution Supersite in Manchester alongside simultaneous measurements of OH, HO2, RO2 and OH reactivity made using our FAGE instrumentation (see Figure 1) (Stone et al., 2012; Whalley et al., 2021), together with a comprehensive suite of supporting gas-phase and radiation measurements, as well as aerosol surface area and aerosol composition, which are all available from the Manchester site.
(3) To use data from (2) above, together with new data from our laboratory, to develop new parameterizations of the rates of uptake of peroxy radicals for inclusion into a box model (zero dimensional model) to quantify aerosol uptake to understand how heterogeneous processes influence ozone. The box model incorporates the Master Chemical Mechanism, which contains ~17,000 reactions and ~7,000 species to describe in detail chemical oxidation in the atmosphere.
The research will lead to an improved representation of chemical oxidation mechanisms in models leading to a better predictive capability of atmospheric composition linking to air quality and climate. You will benefit from using a wide range of instrumentation (lasers, optics, vacuum and gas handling, data acquisition, electronics) and modelling tools, and by working with expert investigators you will receive advanced technical training and enhance your skills base. The Leeds FAGE instrumentation is part of the National Centre for Atmospheric Science. There is scope for further collaboration with atmospheric scientists in Leeds and elsewhere, for example with the group of Professor Mathew Evans at the University of York who will incorporate the new parameterisations of peroxy radical aerosol uptake into regional and global chemistry-transport models. The results from the project will be disseminated widely to the scientific community through high quality publications in leading international journals and at international conferences.
Training
You will work under the supervision of Professor Dwayne Heard and Dr Lisa Whalley from the School of Chemistry at Leeds, who are members of the Atmospheric and Planetary Chemistry Group. The supervisors lead active and vibrant research groups exploring the role of gas-phase and aerosol chemical processes (Lakey et al., 2016) in the atmosphere, using experimental and modelling approaches. We have experience with the ultra-sensitive detection of radicals using laser-induced fluorescence spectroscopy (Stone et al., 2012; Heard and Pilling, 2003; Whalley et al., 2021) as well as chemical modelling using “box” (zero-dimensional) models (Whalley et al., 2021).
You will work in well-equipped laboratories and be part of an active, thriving and well-funded atmospheric chemistry community. The Leeds group is part of the National Centre for Atmospheric Science (NCAS) and the FAGE instrumentation is part of the Atmospheric Measurement and Observation Facility (AMOF), and has an internationally leading reputation in atmospheric chemistry for field measurements of atmospheric composition, laboratory studies of chemical kinetics and photochemistry, and the development of advanced numerical models and chemical mechanisms. Activities in these three areas are intimately linked and interdependent, providing a significant advantage. The PhD will provide a broad spectrum of experience and training in the use of high power lasers, vacuum systems, optics, electronics, computer controlled data acquisition systems and methods in numerical calculations. By working with expert investigators you will receive advanced technical training and enhance your skills base. We will strongly support you to write publications during your PhD and you will be supported to attend both national and international conferences. You will have access to a broad spectrum of training workshops in scientific writing, numerical modelling, through to managing your degree, to preparing for your viva. You will also have opportunities for training provided by the National Centre for Atmospheric Science.
The project will provide opportunities to work alongside other atmospheric scientists in the UK as part of collaborative fieldwork, and also to collaborate with the group of Professor Mathew Evans at the University of York, who will incorporate the new parameterisations of peroxy radical aerosol uptake into regional and global chemistry-transport models. The results from the project will be disseminated widely to the scientific community through high quality publications in leading international journals and at international conferences.
Your Profile
You should have an interest in atmospheric chemistry, air quality, climate and global environmental problems, with a strong background in chemistry or a similar discipline (e.g. physics, engineering, environmental science).
References (click on reference to go to journal paper)