Understanding the atmospheric chemistry of biomass burning emissions and their impact on air quality and climate

Large scale biomass burning events, including wildfires, agricultural burn-off and residential fuel combustion, release large quantities of organic carbon to the atmosphere.  These emissions can then undergo chemical transformations leading to a wide range of secondary gas and particulate products which can have a significant impact upon climate and air quality.

Air quality and climate change are two of the most important environmental issues of our time, impacting human health, ecosystems, and the economy. The World Health Organisation has estimated that globally 8.8 million people die each year as a direct result of exposure to air pollution [1].  Exposure to poor air quality has a range of short and long term impacts on health including a wide range of cardiovascular and respiratory diseases, cancer, diabetes and links to dementia [2].

The frequency and intensity of wildfires in the US, Brazil and Australia have notably increased over the last decade (see Figure 1), and this trend is likely to continue owing to fire/land management practises and climate change [3].  Therefore, it is becoming increasingly important to understand the formation of gas and aerosol phase products from these emissions in order to quantify their impacts and limit their detrimental effects.

Figure 1. Fire count data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite strikingly highlights the extent of biomass burning around the world (https://modis.gsfc.nasa.gov)

In this project we will design a series of experiments to be carried out in a flow reactor built in York to study atmospheric chemistry, in order to understand the most important formation pathways of gas and aerosol phase products from a range of biomass-burning emissions.  These will focus on oxygenated aromatic volatile organic compounds (VOC),  such as furans and phenolic compounds (see Figure 2 and 3) [4, 5, 6, 7].   First,  the flow reactor will be characterised through a set of experiments carried out on aromatic systems whose chemical mechanisms are already available in the Master Chemical Mechanism (MCM: mcm.york.ac.uk).  The loss of the precursor species and the formation of wide range of gas and aerosol phase products will be measured using on and off-line mass spectrometric techniques including PTR-MS (Proton Transfer Reaction mass spectrometry) and SIFT-MS (Selected Ion Flow Tube mass spectrometry) for gas phase species, and UPLC (ultra-high pressure liquid chromatography) coupled to Orbitrap mass spectrometry for investigating secondary organic aerosol composition. Experiments will be designed using box models based around the detailed chemistry available in the MCM, optimised for the conditions of the flow reactor.   Newly developed and evaluated chemical mechanisms for emitted biomass burning compounds will subsequently be incorporated into the MCM.

Figure 2. Schematic of biomass burning emissions of some important oxygenated aromatics, whose atmospheric chemistry will lead to the formation of a wide range of multifunctional gas and aerosol phase secondary products that can have a significant detrimental impact on climate, air quality and health [4, 5, 6].

Figure 3. Results from residential burning studies of different types of domestic fuels used in Delhi, India showing the relative species contributors to secondary organic aerosol formation (SOA) under (A) high NOx conditions and (B) low NOx conditions.  Both plots highlight the dominant contributions from the emissions of phenols + furans [7]
More specifically, during this research project you will gain experience of:

  • Using a new flow reactor facility in order to investigate the atmospheric chemistry of important oxygenated aromatic species emitted in significant quantities from biomass burning
  • Development and optimisation of the flow reactor to carry out time resolved experiments, under a range of conditions:
    1. OH, NO3 and O3 radical initiated chemistry
    2. Experiments carried out over a range of NOx/VOC conditions
    3. Experiments carried out at different relative humidities, with and without seed aerosol
  • Using chemical box models incorporating the Master Chemical Mechanism (MCM: mcm.york.ac.uk) to design and optimise experiments and evaluate the chemistry for the target biomass burning precursor species.
  • Using of a range of on and off-line mass-spectrometry methods to detect, identify and quantify gas and aerosol phase products.

The student will work under the supervision of Dr Andrew Rickard (chemical mechanism development, chamber experiments), Professor Jacqui Hamilton (aerosol composition measurements, chamber experiments) and Dr Marvin Shaw (speciated measurements of VOC using mass spectrometry).  The student will be based in the Wolfson Atmospheric Chemistry Laboratories (WACL), part of the Department of Chemistry at the University of York (www.york.ac.uk/chemistry/research/wacl/). WACL is a world leading facility bringing together experts in atmospheric measurements, lab-studies and Earth system modelling to form the UK’s largest integrated atmospheric science research team.

The studentship is offered as part of the NERC PANORAMA Doctoral Training Programme,  which will provide training in addition to that offered by the department in York.  A wide range of training opportunities are available, including courses aimed at specific science objectives, at improving your transferable skills and putting your work into a wider scientific context.  Drs Rickard and Shaw both work for the National Centre for Atmospheric Science (NCAS, https://ncas.ac.uk/en/air-quality), and thus the student will have access to the wider resources that NCAS provides including the Arran Atmospheric Measurement Summer School, the Earth System Science Summer School (ES4), and future further developments in computations and data analysis.

The student should have a strong background in the physical sciences (i.e. a good degree in chemistry, physics, engineering or similar science), a keen interest in environmental issues, and an aptitude and enthusiasm for experimental work.

We appreciate that this PhD project encompasses several different science and technology areas, and we don’t expect applicants to have experience in many of these fields. The project is well supported with experienced scientists and training in these new techniques and disciplines is all part of the PhD.

References

[1]  World Health Organization. Global Health Observatoryhttp://www.who.int/gho/en/

[2]  Defra, Clean Air Strategy, 2019, https://www.gov.uk/government/publications/clean-air-strategy-2019

[3]  Spracklen, DV;  Mickley, LJ;  Logan, JA;  Hudman, RC;  Yevich, R;  Flannigan, MD; and Westerling, AL: Impacts of climate change from 2000 to 2050 on wildfire activity and carbonaceous aerosol concentrations in the western United States, J. Geophys. Res. Atmos., 114(20), 1–17, doi:10.1029/2008JDO10966, 2009.

[4]  Coggon, MM; Lim, CY; Koss, AR; Sekimoto, K; Yuan, B; Gilman, JB; Hagan, DH; Selimovic, V; Zarzana, KJ; Brown, SS; Roberts, JM; Muller, M; Yokelson, R; Wisthaler, A; Krechmer, JE; Jimenez, JL; Cappa, C; Kroll, JH; de Gouw, J; and Warneke, C: OH chemistry of non-methane organic gases (NMOGs) emitted from laboratory and ambient biomass burning smoke: evaluating the influence of furans and oxygenated aromatics on ozone and secondary NMOG formation, Atmos. Chem. Phys., 19, 14875–14899, 2019 https://doi.org/10.5194/acp-19-14875-2019.

[5]  Finewax, Z; de Gouw, JA; Ziemann, PJ: Aerosol Yields from the OH and NO3 Radical-Initiated Oxidation of Resorcinol, ACS EARTH AND SPACE CHEMISTRY, 3  (7), 1248-1259, DOI: 10.1021/acsearthspacechem.9b00112, 2019

[6]  Jiang, J; Carter, WPL; Cocker, DR and Barsanti, KC: Development and Evaluation of a Detailed Mechanism for Gas-Phase Atmospheric Reactions of Furans, ACS EARTH AND SPACE CHEMISTRY, 4  (8), 1254-1268, doi: 10.1021/acsearthspacechem.0c00058, 2020.

[7]  Stewart, GJ; Nelson, BS; Acton, WJF; Vaughan, AR; Hopkins, JR; Yunus, SSM; Hewitt, CN; Nemitz, E; Rickard, AR; Lee, JD and Hamilton, JF:  Comprehensive organic emission profiles, secondary organic aerosol production, reactivity and toxicity of emissions from domestic fuels in Delhi, India, Submitted to Atmospheric Chemistry and Physics Discussions, August 2020