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Understanding the sources of volatile organic compounds in Delhi, India

Dr Sarah Moller (WACL, University of York), Dr Jacqui Hamilton (WACL, University of York)

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Outdoor air pollution is responsible for 3.7 million premature deaths worldwide and UNEP declared it to be the world’s worst environmental health risk (UNEP 2014). It is particularly an issue in developing countries where industrial, traffic and urban emissions have increased rapidly (Ghude et al., 2013). 34 of the top 100 most polluted cities are in India (WHO, 2016) but air quality measurements in Indian cities are sparse. Across Delhi for example there are only 10 air quality measurement sites compared to the > 100 monitoring sites across Greater London, which is broadly comparable in population size and density. The lack of monitoring data limits the ability to quantify current pollutant concentrations, health impacts from exposure to pollution and the development of appropriate assessment and mitigation tools.

Emission inventories for Delhi are also inadequate, lacking spatial resolution and representation of individual point and road sources (see Figure 1). This limits the ability to forecast air quality and creates considerable uncertainty in projecting outcomes of policy interventions such as traffic management. The improvement of emission inventories and understanding of key sources is important to allow better air quality projections to be made providing support for the development of policies and practices that ensure that economic growth does not further deteriorate India’s air quality.

Figure 1: A. Modelled iso-concentration plot for nitrogen oxides in Delhi based on the most recent emissions inventory for summer (Left) and post monsoon (Right) periods. B. London2012 average concentrations of nitrogen oxides predicted by ADMS urban modelling.

Volatile organic compounds (VOCs) are emitted from a huge variety of natural and man-made sources. In the urban atmosphere VOCs lead to the formation of ozone and particulate matter (PM). For policy development it is useful to have speciation of the VOCs present as different molecular structures lead to different yields of ozone and PM. These secondary pollutants have significant health impacts and so control strategies are needed to limit emissions of precursors and therefore the concentrations of these harmful pollutants. Even in developed cities our understanding of reactive carbon is still evolving and in Delhi, where fuel composition and modes of usage may be highly variable the VOC speciation is also likely to vary across the city.

The key anthropogenic sources of reactive carbon are from road transport (evaporative fuel releases, tailpipe), incomplete combustion, and various industrial usage. Delhi and the wider National Capital Territory face specific challenges that arise from the use of variable and frequently poor quality/unregulated fuels and the resulting combustion products from road transport and small-scale electrical power generation. Little is known about the detailed speciation of VOCs in Delhi, although there are anecdotal reports of very high levels of toxic species (such as 1,3-butadiene) in the Delhi atmosphere arising from evaporative and tailpipe emissions.


In this project, you will work with leading scientists at the Wolfson Atmospheric Chemistry Laboratories (WACL) at the University of York to make measurements of volatile organic compounds at locations around Delhi contributing to the characterisation of air pollution across the city. This project is part of the wider Delhi-AIRQUALNET project, which aims to provide the most comprehensive observations of air pollutant concentrations, sources and emissions in Delhi to date.

The PhD project would include

  1. Assisting with the analysis of whole air samples taken from locations around Delhi. Analysis would be carried out for speciated volatile organic compounds (VOCs), methane and carbon dioxide (CO2). Techniques will include gas chromatography with flame ionisation detection for CO2 and methane and by comprehensive two-dimensional gas chromatography for the non-methane VOCs.
  2. Comparison of high quality chromatographic measurements of CO2 from weekly samples with CO2 measurements from an air quality sensor network run by the University of Cambridge. This will allow the weekly averaged data to be put into the context of the more variable high time resolution sensor data.
  3. Analysis of fuel samples by two-dimensional gas chromatography coupled to mass spectrometry to provide improved source speciation profiles of unburnt fuel/evaporative emissions.
  4. Characterisation of the impact of factors such as season, meteorology and location on VOC emission and speciation.  Co-variance with other pollutants may also be looked at.
  5. Assessment of the most important VOCs in Delhi’s atmosphere for production of secondary pollutants and health impacts.

Potential for high impact outcome

Developing economies such as India must maximise air quality improvements in the shortest time possible but with acceptable economic costs. In order to achieve this there is a need for policy informed by scientific understanding. This work will contribute to the aims of the AIRQUALNET project as a whole to provide critical knowledge of pollutant concentrations and their sources, which are essential for developing mitigation strategies. The outcomes of the project are designed to be directly useful to practitioners tasked with managing air pollution in Delhi. The research should also provide high quality research papers.


The student will work under the supervision of Dr. Sarah Moller and Dr. Jacqui Hamilton 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. 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.

Drs Hamilton and Moller will provide comprehensive training in the technical aspects of the analytical instrumentation, data analysis and interpretation.

Student profile

The student should have an interest in global environmental problems and a strong science background (e.g. chemistry, physics, environmental sciences, forensic science). Interest in and experience of analytical science would be beneficial but training will be given to enable the successful student to carry out the work involved in this project. The student must be willing to travel outside the UK.


Ghude, S.D., G.G. Pfister, C. Jena, R.J. van der A, L.K. Emmons and R. Kumar, Satellite constraints of nitrogen oxide (NOx) emissions from India based on OMI observations and WRF-Chem simulations. Geophys. Res. Lett., 2013, 40, doi:10.1029/2012GL053926.

UNEP, 2014. UNEP Year Book 2014: Emerging issues in our global environment. Available at

WHO 2016, World Health Organisation, Global Urban Ambient Air Pollution Database topics/outdoorair/databases/cities/en/

Related undergraduate subjects:

  • Chemistry
  • Environmental science
  • Forensic science
  • Physics