Project highlights

  • Build a better understanding of nitrogen compounds’ atmospheric chemistry and their roles in determining air quality 
  • Conduct collaborative fieldwork at one of the UK’s air quality supersites 
  • Gain expertise in using highly sensitive instrumentation to record air pollutants  


Air pollution is responsible for around 350,000 premature deaths per year in Europe [1] and 7 million globally [2]. In the UK and in Europe, the three most toxic air pollutants are NO2 (nitrogen dioxide), tropospheric O3 (ozone) and PM (particulate matter). NO2 and PM are emitted directly from various human-made sources and a few natural sources, but the majority of NO2 comes from road vehicles. Substantial decreases in NO2 concentrations were observed during COVID lockdown restrictions when people’s activity was severely reduced [1,3]. Contrastingly, tropospheric ozone is not emitted directly but rather it is produced within the atmosphere itself from the photochemical oxidation of volatile organic compounds in the presence of nitrogen oxides (NOx = NO+NO2). Some types of PM are also generated and/or chemically transformed in the atmosphere. Controlling these secondary air pollutants is challenging because it requires control of their precursors, and such efforts must be informed by a thorough understanding of the chemical pathways.  

Observations of air pollutants are vital. The UK’s main monitoring is done by the Automated Urban and Rural Network (AURN) which runs 150 air monitoring sites [4]. Additionally, three “air quality supersites” have been established that contain more extensive instrumentation for conducting detailed studies of atmospheric composition and variability. One supersite is on Birmingham University’s campus [5], where this project will deploy additional research instruments from our group to quantify oxidised nitrogen compounds.  

To further complicate the picture, air pollutant concentrations are highly dynamic, especially close to pollution sources. As an example, Figure 1 shows measurements of NO2 and aerosol optical depth (related to PM concentrations) made close to a roadside over a brief 10 minute interval. Concentrations can change by a factor of 3 in just a few seconds with the passing traffic. Notice also how some vehicles were strong emitters of both NO2 and aerosol (peaks at 15:21:40 and 15:22:27); others emitted aerosol but only small amounts of NO2 (15:15:55 and 15:17:12); and others strongly emitted NO2 but very little aerosol (15:19:47). 

A graph showing a time series of roadside NO2 and aerosol.

Figure 1: A time series of emissions from road vehicles. NO2 mixing ratios are in red, overlaid by wavelength-resolved aerosol extinctions (coloured as stated in the legend). The BBCEAS instrument sampled from a second-storey window of a university building overlooking a public road. 


University of Leicester


  • Climate and Environmental Sustainability


Project investigator

Dr Stephen Ball ([email protected]), University of Leicester.


Prof Paul Monks ([email protected]), University of Leicester. 

Prof Bill Bloss ([email protected]), University of Birmingham. 

How to apply


The CENTA student will use a broadband cavity enhanced absorption spectrometer (BBCEAS) built at Leicester University. This instrument acquired the data shown in Figure 1. A light beam is reflected many times through ambient air samples, thereby producing a highly sensitive measurement. The instrument is configurable for different nitrogen-containing trace gases: (i) simultaneous measurements of HONO and NO2 (HONO is a source of OH radicals) [6], (ii) fast timeresolution NO2 observations [Figure 1], (iii) quantifying the night-time NO3 radical and its reservoir compound N2O5 [7]. It is anticipated that the student will measure different oxidised nitrogen species at different stages of the project to complement the ongoing “core” observations at the Birmingham supersite, plus a more intensive measurement period to study the formation of aerosol nitrate from the deposition of N2O5 and HNO3.  

Training and skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD.  

This project would suit a candidate who has a strong background in experimental physical chemistry (gas-phase spectroscopy, reaction kinetics etc), atmospheric chemistry, or analytical chemistry (instrumentation, field sampling), and who wants to apply their knowledge.  

The student will receive specific training to operate Leicester’s research instruments and analyse their data. There will be extensive opportunities to work with colleagues at Birmingham who run the BAQS supersite and operate its suite of state-of-the-art commercial instruments. Leicester’s School of Chemistry offers lecture courses directly relevant to the project, e.g. Earth System Science. Additionally, the cohort of CENTA students organise their own seminars and conferences. 

Partners and collaboration

University of Birmingham: The Birmingham Air Quality Supersite (BAQS) is a state-of-the-science urban background air quality monitoring station, on the Edgbaston campus of the University of Birmingham, 2 miles south-west of the city centre.  Instrumentation at BAQS covers gas-phase species (NOx, O3, NH3, VOCs, CO2), aerosol physical characteristics (ultrafine particles, PM mass concentration, PM size distribution), aerosol chemical composition (inorganics and metals), and meteorological & photochemical parameters. There is space to host visiting instruments.  Recently, BAQS has supported baseline air quality measurements for the Commonwealth Games, and an intensive campaign within the NERC-funded OSCA project to explore NOy speciation in wintertime. 

Further details

Further details on how to contact the supervisor for this project and how to apply for this project can be found here: 

For any enquiries related to this project please contact Dr Stephen Ball ([email protected]), University of Leicester, or Prof Bill Bloss ([email protected]), University of Birmingham. 

To apply to this project: 

  • You must include a CENTA studentship application form, downloadable from: CENTA Studentship Application Form 2024. 
  • You must include a CV with the names of at least two referees (preferably three) who can comment on your academic abilities. 
  • Please submit your application and complete the host institution application process via:  Please scroll to the bottom of the page and click on the “Apply for NERC CENTA Studentship” button.  Your CV can uploaded to the Experience section of the online form, the CENTA application form 2024 can be uploaded to the Personal Statement section of the online form.  Please quote CENTA 2024-L1-CENTA2-CHEM1-BALL  when completing the application form. 

Applications must be submitted by 23:59 GMT on Wednesday 10th January 2024. 

Possible timeline

Year 1

Year 1: CENTA’s core research skills training. And training specific to this project – the student will be taught how to operate the BBCEAS instrument and how to use the software needed to fit BBCEAS spectra to retrieve the concentrations of target gases. The instrument’s most straightforward configuration is to measure NO2. Thus the student will perform a “dry run” campaign measuring ambient NO2 and compare their results with NO2 data recorded by the AURN monitoring station located on the Leicester University campus 

Year 2

Year 2: Measurements at BAQS. An instrument inter-comparison of HONO measurements by BBCEAS at UV-wavelengths and HONO measured by BAQS’s quantum cascade laser (QCL) system. BBCEAS measurements of N2O5 at BAQS, together with the site’s core instrumentation, to investigate aerosol composition and concentration change, with a focus on the production of aerosol nitrate.  

Year 3

Year 3 into 4: The BBCEAS instrument is sufficiently compact to be operated from battery power for several hours. This enables mobile measurements to be performed from a moving vehicle. Possible further investigation of real on-road NO2 and HONO concentrations [6], or transect measurements of oxidised nitrogen species across the city. Student prepares & submits a publication to a high-impact, peer-reviewed journal with the student as the first named author. Write and submit thesis. 

Further reading

[1] “Air quality in Europe – 2021 report”, European Environment Agency (2021),  

[2] The Lancet Commission on pollution and health, P.J. Landrigan et al., (2018) vol 391, issue 10119, 462-512, 

[3] Changes in ambient air quality and atmospheric composition and reactivity in the South East of the UK as a result of the COVID-19 lockdown, K.P. Wyche , M. Nichols, H. Parfitt, P. Beckett, D.J. Gregg, K.L. Smallbone, and P.S. Monks, Science of the Total Environment 755, 142526, (2021),  

[4] Automatic Urban and Rural Network (AURN), 

[5] Air quality supersites,  

[6] Nitrous acid (HONO) emissions under real-world driving conditions from vehicles in a UK road tunnel, L.J. Kramer, L.R. Crilley, T.J. Adams, S.M. Ball, F.D. Pope, and W.J. Bloss, Atmos. Chem. Phys., 20, 5231–5248, (2020),  

[7] Atmospheric chemistry at night, S.M. Ball, (2014),