Understanding the changing sources of volatile organic compounds in the UK over the last two decades and implications for the future

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Understanding the changing sources of volatile organic compounds in the UK over the last two decades and implications for the future

Introduction

Volatile Organic Compounds (VOCs) are emitted into the atmosphere from a wide variety of sources and can be anthropogenic (man-made) or biogenic (naturally produced) in origin.  Dominant sources of hydrocarbons vary greatly on global and regional scales, depending upon the population, vegetation and industry within the surrounding environment.  This variation in source strength often leads to a corresponding variation in the significance of different species.  Once emitted into the atmosphere, VOC concentrations are influenced by a number of factors including meteorology, dry and wet deposition and chemical reactions.  The atmospheric chemistry of VOCs is dominated by the hydroxyl radical which leads to their oxidation at a range of timescales, from hours to months, dependent upon their structure.  Ultimately their oxidation leads to the formation of carbon dioxide (CO2), an important climate gas.  Their greatest significance to the atmosphere, however, is the secondary pollutants produced during their oxidation which tend to be more harmful, including ozone, formaldehyde and other highly oxygenated compounds which are all implicated as key contributors to respiratory illnesses in people as well as limiting crop yields through damage to plant stomata and leaves.  The efficiency with which different VOCs can produce these important secondary pollutants in the atmosphere is dependent upon their structure so it is, therefore, vitally important to make observations of individual (speciated) VOCs in the atmosphere as a bulk measurement of the total VOC concentration tells us very little about their potential for harm.

 

Three new UK atmospheric observatories have been installed in 2019 at locations in London, Birmingham and Manchester for the observation of the atmosphere in different urban centres.  State-of-the-art instrumentation has been deployed at each of these sites for the measurement of a range of trace gases (including ozone, oxides of nitrogen and VOCs) and aerosols as well as local meteorology.  The technique selected for the observation of VOCs is gas chromatography coupled with flame ionisation detectors to provide the required speciated observations while maintaining the robustness required for long-term deployment of instruments.  Three identical instruments have been installed at the three locations in order to simplify instrument operation and maintenance as well as data comparison from the different observatories.  The VOC data obtained undergoes thorough data quality checks before being finalised, however, this project will investigate the automation of many of these checks in order to release near-real-time data for VOCs which could be applied to Air Quality forecasting models and assessments on shorter timescales than is currently possible.

Figure 1:  Shows the Honor Oak “urban background” observatory in South London where observations of VOCs in the atmosphere are made.  The site also houses a wide range of other trace gas and aerosol instruments.  The same instrumentation operated at sites in Manchester and Birmingham help scientists to understand composition changes at urban background locations in the UK.

 

The UK has a highly detailed emissions inventory encompassing hundreds of different chemical species from thousands of individual sources.  Emission estimates originate from a variety of methods depending on the source under consideration, but validation of the accuracy of the inventory output has received relatively little attention, partly due to the complexity of such an undertaking.  In this project, we will compare the emissions inventory outputs with observations from the three new observatories to assess the current emissions inventory as well as use historic, publically available, data from other UK monitoring stations to investigate the inventory over the last three decades or so.  Data collected during short-term UK deployments will also be used in order to widen the comparison to other areas of the UK.

Figure 2:  Total UK VOC emissions as predicted by the National Atmospheric Emissions inventory.  The rapid decrease (particularly from the road transport sector) since the 1990s is evident along with the levelling-off in recent years.  The changing composition during this time, due to the changing dominance of individual sources will be investigated during the project.

Figure 3:  Benzene data taken from the National Atmospheric Emissions Inventory (NAEI) showing (a) the total emissions for benzene in the UK, (b) emissions from road transport and (c) emissions from the extraction and distribution of fossil fuels.  The plots show that, in the case of benzene, its emissions are dominated by road transport, however, the plots also show that the extraction and distribution of fossil fuels can be significant point sources in certain areas

 

Project Aims

This project aims to:

  1. Provide the UK with continuous measurements of VOCs at three urban sites in order to better understand their role in the UK atmosphere. Comparisons between different cities will be made to identify the significance of different localised sources and meteorology to their ambient concentrations.  Providing near real-time, automated observations will provide important information regarding local air quality at these locations.

 

  1. The data produced will be placed in the context of historic data collected at UK air quality sites and short-term deployments of equipment during field projects in the UK to investigate the changing composition of the contributions of individual source sectors to the ambient VOCs over the last thirty years.

 

  1. Current and historic observations of VOCs will be compared to the National Atmospheric Emissions Inventory outputs to evaluate its effectiveness in predicting ambient levels of VOCs in the UK

 

 

Training

The student will work under the supervision of Prof Jacqueline Hamilton and Dr Jim Hopkins (University of York) and will be based at the Wolfson Atmospheric Chemistry Laboratories, part of the University of York Department of Chemistry (YDC).  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.  The studentship is offered as part of the PANORAMA Doctoral Training Program, which provides additional training.  Through the Department of Chemistry, University of York and PANORAMA training there are a wide range of activities including courses aimed at specific scientific objectives, improving transferrable skills, completing your PhD and putting your work into a wider scientific context. Dr Hopkins works for the National Centre for Atmospheric Science (NCAS), and thus the student will have access to the wider resources that NCAS provides including the Arran instrumental Summer School, the Earth System Science Summer School (ES4), and future further developments in computations and data analysis.

 

Under the supervision of Prof Hamilton and Dr Hopkins, the student will develop transferable skills in using gas chromatography for making high-precision, quality controlled and assured observations of speciated VOCs in the atmosphere.  They will apply data analysis tools for measurement comparison and analysis of long term trends of atmospheric gases using a variety of statistical techniques.  They will also gain understanding and knowledge to enable them to place their observations in the wider context of historical, regional and global composition.

 

This studentship will be based in the Wolfson Atmospheric Chemistry Laboratories (WACL), a world leading facility bringing together experts in atmospheric measurements, Earth system models and lab-studies to form the largest integrated UK atmospheric science research team. These were established in 2013 and comprise a state of the art 1200 m2 dedicated research building, the first of its kind in the UK. 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).

 

Applicants should have a First or 2:1 degree in Chemistry, Physics, Computing, Environmental Sciences or a related discipline, or have a 2:2 degree and a Masters qualification. 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.