The majority of the World’s population lives in heavily urbanized areas impacted by high levels of pollution, which can have severe detrimental effects on air quality and human health. A recent study showed that around 4,000 people die each day in China as a result of exposure to air pollution. Megacities, large densely populated urban regions, often suffer from particularly high concentrations of air pollutants due to a high density of emission sources such as road traffic and regional biomass burning. One such example is Beijing, a Chinese megacity with a population of > 20 million, whose air quality problems are well documented in the media. Although Beijing’s air quality has improved in recent years, some important pollutants are still above recommended guidelines, such as particulate matter (PM) and ozone. Therefore, it is important to understanding what factors are controlling urban air quality so that we can formulate appropriate strategies to mitigate these problems.
During the recent Air Pollution and Human Health in a Chinese Megacity measurement campaign in Beijing, it was observed that oxidised organic material accounted for up to 90% of the total particulate organic mass during the winter. This material is most likely formed via the oxidation of volatile organic compounds in the atmosphere to form secondary organic aerosol (SOA). Aerosol mass spectrometry identified the main sources of organic particulate matter as coal combustion, cooking, biomass burning and oxidised organic material. Analysis of particle samples collected in Beijing during this time indicates that nitrophenol compounds make up a significant fraction of the observed organic mass. These compounds may have significant effects on humans, due to their potential cancer risk from exposure, are harmful to ecosystems as a phytotoxin and climate as a source of brown carbon. The amounts of nitrophenols observed in Beijing are much higher than in previous urban studies. However, the sources of this material is unclear. The two most likely sources are from the photo-oxidation of aromatics, coming from petrol and diesel exhaust emissions and regional biomass burning.
The overall aim of this project is to study the detailed formation and degradation mechanisms of atmospherically important nitrophenol compounds through the design and analysis of comprehensive chamber simulation experiments carried out using the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences indoor atmospheric simulation chamber facility.
A key objective of the project is to improve our understanding and representation of key phenolic oxidation chemistry in the Master Chemical Mechanism (MCM: http://mcm.leeds.ac.uk/MCM
). New detailed chemical schemes for phenolic degradation pathways will be developed and updated based on the results of recent studies. The new chemical schemes will be incorporated into chamber specific box models to help design and interpret the experiments in the Guangzhou chamber for a range of representative conditions. The performance of the new mechanisms will initially be evaluated against the current MCM, in terms of ability to represent the formation of ozone, NOx and measured oxygenated organic products, with the results used to further optimize the schemes.
Two sets of chamber experiments will be carried out in August 2019 and January 2020. This studentship will include the opportunity to visit the chamber in Guangzhou and play an active role in the experiment design.
Experiments will be carried out on the most abundant nitrophenols observed in Beijing aerosol samples; 2-nitronaphthol, 4- nitrophenol and 2-methyl-3-nitrophenol. We will study their most likely precursors based on known reaction schemes; phenol, benzaldehyde, methyl-phenols, and naphthalene , as well as dihydroxy-aromatics, also observed in Beijing and are used as biomass burning tracers. Experiments will simulate both the daytime oxidation by OH radicals in the presence of NOx and night-time oxidation by NO3.
From these experiments we will gain a detailed understanding of the sources and formation processes of nitrophenols and secondary organic aerosol from the atmospheric oxidation of aromatics and phenolic species, under conditions observed in the Beijing urban atmosphere, including the role that day vs. night-time chemistry plays in their chemical evolution.
The successful applicant will work closely with leading UK and Chinese experts in atmospheric chemical mechanism development, detailed chemical modelling, chamber simulation experiments and aerosol composition measurements.
Key words: Aerosols, Air Quality, Atmosphere, Chemistry, Fieldwork, Laboratory, Modelling, Ozone, Pollution
This PhD will formally start on 1 October 2019. Induction activities will start on 30 September.