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Improving our understanding of the role of biogenic emissions in urban air quality

Dr Jacqui Hamilton (YDC), Dr Andrew Rickard (YDC)

Contact email: jacqui.hamilton@york.ac.uk

Introduction

Exposure to poor air quality is the top environmental risk factor of premature mortality across the globe [1]. Heart disease and strokes are the most common reasons for premature deaths due to air pollution, with other significant impacts including increased respiratory and cardiovascular disease and cancer.  In many urban areas, one of the most important pollutants for health is particulate matter.  Previous studies of the isotopic signature of carbonaceous material in particles indicate that a large fraction of particle mass is from natural sources [2]. These sources include biomass burning, cooking and the oxidation of volatile organic compounds emitted from plants to form secondary organic aerosols (SOA).

A recent modeling study predicted biogenic emissions, in particular isoprene, dominate the production of SOA in Beijing in summer, as shown in Figure 1. However, atmospheric models can only incorporate a small number of sources and chemical reactions and need to be validated with field measurements. The relative importance of biogenic versus anthropogenic SOA is difficult to determine using conventional field field-based techniques that look at the bulk functionality of particles.  High-resolution chemical speciation can be used to investigate source specific tracers, however this approach typically only characterizes a very small fraction of the particle mass [3].

Figure 1:  Predicted time series of SOA concentrations and fractional contributions to SOA due to different precursors in Beijing in August 2013. Units are μg m-3. ARO:aromatics; ISOP: isoprene; TERP: monoterpene; SESQ: sesquiterpene;[M]GLY: glyoxalCmethylglyoxal directly emitted or from other precursors; OTHER: boundary conditions. From Hu et al., Atmos. Chem. Phys., 17, 77-92, https://doi.org/10.5194/acp-17-77-2017, 2017.

Project Description

This project aims to improve our understanding of the role of biogenic secondary organic aerosols in urban SOA formation.  The University of York has developed an extensive mass spectral library of tracer molecules that can be used to chemically “fingerprint” specific volatile organic compound (VOC) emissions/sources.  This has been built using a novel atmospheric simulation chamber, where a single VOC precursor can undergo atmospheric reactions in a controlled manner.  Initially the student will improve the coverage of biogenic SOA tracers using a photochemical flow reactor developed at York to allow large quantities of SOA mass to be produced for a range of chemical analyses. The student will use this mass spectral library to compare and contrast the biogenic SOA signatures from time resolved filter samples taken from three large megacities (London, Beijing and Delhi).

The project, based in the world leading Wolfson Atmospheric Chemistry Laboratories, will use state of the art ultra-high resolution mass spectrometry. The student will investigate the factors that control the oxidation and abundance of biogenic SOA and develop methods to estimate the total biogenic loading using source apportionment.  It is expected that the student will collect particle samples during the Dehli-FLUX field campaign and from London field sites.

Recent studies have shown that during the ozonolysis of important biogenic emissions, such as isoprene and monoterpenes, reactive products known as stabilised Criegee intermediates, plays a key role in SOA formation [4].  However, the reaction pathways and potential atmospheric relevance of SCI species are still unknown.  The group at York have previously discovered novel reaction pathways that enhance SOA formation [5] and identified previously unknown sources of SOA [6]. The student will also carry out laboratory simulations of biogenic SOA formation using the photochemical flow reactor and use a range of analytical tools to identify the products of Criegee intermediate reactions, and predict chemical pathways for SOA formation.

Figure 2:  Formation of Criegee Intermediates during the ozonolysis of alkenes.  Further reactions of Criegee Intermediates can form oxidised products and may play a key role in formation of SOA.  

Objectives

The overall aim of this project is to improve our understanding of the impact of biogenic secondary organic aerosol to poor air quality in urban areas.  Therefore, the main objectives of the project are;

  • Carry out atmospheric simulations of key biogenic emissions to understand the role of stabilised Criegee intermediates (SCI) in SOA formation
  • Enhance the York mass spectral “chemical fingerprint” database with additional biogenic SOA tracer molecules.
  • Analyse particle samples collected in Delhi as part of the NERC funded Air Pollution and Human Health Programme’s Delhi-FLUX field campaigns. The student will use ultra high performance liquid chromatography coupled to Orbitrap mass spectrometry in order to analyse the detailed chemical compositions of the samples.
  • Determine the contribution of biogenic SOA to particulate matter in three contrasting megacities (London, Beijing and Delhi)

Potential for high impact outcome

As well as the likely significant scientific outcomes of the project, there are potentially wider impacts that this work will have. The research will directly benefit policymakers, such as Department of Environment, Food and Rural Affairs in the UK and the Chinese Department of Environmental Protection. It also has a potentially large impact for the general public, in terms of understanding the impact of biogenic emissions on urban air quality. There is a growing interest in air pollution in large megacities because of the significant health problems caused.  The results from this project will feed into a large community of scientists from the UK, China and India, working within the NERC funded Air Pollution and Human Health programs.

Training

The student will work under the supervision of Dr. Jacqui Hamilton and Dr Andrew Rickard at the Wolfson Atmospheric Chemistry Laboratories (WACL), part of the University of York’s Department of Chemistry.  

The successful PhD student will have access to a broad range of training workshops put on by the University of York as part of its Innovative Doctoral Training Program (iDTP). The studentship is offered as part of the SPHERES Doctoral Training Program which will provide additional training. Through the Department of Chemistry, University of York and SPHERES training there are a wide range of activities including courses aimed at specific scientific objectives, improving your transferrable skills, completing your PhD and putting your work into a wider scientific context.

Dr Hamilton will provide comprehensive training in the technical aspects of the instrumentation used and data analysis. Dr Andrew Rickard will provide expertise on Criegee intermediate reaction mechanisms.  Dr Rickard is part of the National Centre for Atmospheric Science (NCAS), and thus the student will have access to the wider resources that NCAS provides. You will also have access to training provided by NCAS such as the Arran Summer School, the Earth System Science Summer School (ES4), and future further developments in programming and data analysis. 

The student will work in the Wolfson Atmospheric Chemistry Laboratories, part of the department of Chemistry, University of York.  These were established in 2013 and comprise a state of the art 800 m2 dedicated research building, the first of its kind in the UK. Supported by a large award from the Wolfson Foundation and a private donor, the Laboratories enable experimental and theoretical studies relating to the science of local and global air pollution, stratospheric ozone depletion and climate change. The Laboratories are operated as collaborative venture between the University of York and the National Centre for Atmospheric Science (NCAS), co-locating around 40 researchers from seven academic groups and from NCAS. The Laboratories are also home to independent research fellows, postdoctoral researchers, PhD students and final year undergraduate research projects.

The student will have the opportunity to present their work to the scientific community at national and international meetings and conferences. They will also be encouraged to take part in outreach events organised by both WACL and NCAS in order to disseminate the research beyond the immediate scientific community (e.g. to policymakers and the general public).

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 very well supported with experienced scientists and training in these new techniques and disciplines is all part of the PhD.

References

  1. WHO, 2013, Review of evidence on health aspects of air pollution- REVIHAAP Project, Technical Report, World Health Organization, Regional Office for Europe, Copenhagen, Denmark.
  2. Szidat, S., Jenk, T.M., Synal, H.-A., Kalberer, M., Wacker, L., Hajdas, I., Kasper-Giebl, A., Baltensperger, U., 2006, Contributions of fossil fuel, biomass-burning, and biogenic emissions to carbonaceous aerosols in Zurich as traced by 14C, Journal of Geophysical Research Atmospheres, 111, art. no. D07206, DOI: 10.1029/2005JD006590.
  3. Nozière, B., Kalberer, M., Claeys, M., Allan, J., D'Anna, B., Decesari, S., Finessi, E., Glasius, M., Grgić, I., Hamilton, J.F., Hoffmann, T., Iinuma, Y., Jaoui, M., Kahnt, A., Kampf, C.J., Kourtchev, I., Maenhaut, W., Marsden, N., Saarikoski, S., Schnelle-Kreis, J., Surratt, J.D., Szidat, S., Szmigielski, R., Wisthaler, A., 2015, The Molecular Identification of Organic Compounds in the Atmosphere: State of the Art and Challenges Chemical Reviews, 115, 3919-3983. DOI:10.1021/cr5003485
  4. Mackenzie-Rae, F. A., Wallis, H. J., Rickard, A. R., Pereira, K., Saunders, S. M., Wang, X., and Hamilton, J. F., 2017, Ozonolysis of α-phellandrene – Part 2: Compositional analysis of secondary organic aerosol highlights the role of stabilised Criegee intermediates, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-654, in review.
  5. Hamilton, J.F., Lewis, A.C., Reynolds, J.C., Carpenter, L.J., Lubben, A., 2006, Investigating the composition of organic aerosol resulting from cyclohexene ozonolysis: Low molecular weight and heterogeneous reaction products Atmospheric Chemistry and Physics, 6, 4973-4984.
  6. Hamilton, J.F., Lewis, A.C., Carey, T.J., Wenger, J.C., Garcia, E.B.I., Muñoz, A., 2009, Reactive oxidation products promote secondary organic aerosol formation from green leaf volatiles, Atmospheric Chemistry and Physics, 9, 3815-3823. 

Related undergraduate subjects:

  • Atmospheric science
  • Chemistry
  • Earth science
  • Environmental science
  • Physics