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Volatile Organics Indoor Lifetime Assay (VOILA!)

Dr. Terry Dillon (WACL, University of York), Prof. Ally Lewis (WACL, University of York)

Project partner(s): Givaudan (potential CASE)

Contact email:

This is a project to study the lifetimes, chemistry and impacts of reactive volatile organic compounds (VOC) in indoor air environments. VOC are widely used in many cleaning / personal care products in the home and for a variety of industrial purposes. A detailed understanding of the oxidation pathways that degrade VOC indoors is key to improving product performance, maintaining good indoor air quality and the optimising the design of next generation buildings.

Considerable effort over 50 years has been directed to the study of VOC chemistry in the natural, outdoor environment, and impacts on air-quality, human, animal and plant health, and climate are all now widely appreciated. By contrast, indoor air chemistry and the reactivity of VOC indoors is relatively poorly understood. Particulates and a variety of VOC can be present indoors, often a result of open-fires, cooking or from mixing in of polluted outdoor air. According to the World Health Organisation, 4.3 million people a year die from exposure to household air pollution, largely in the developing world[1].

In Western societies, it is recognised that humans spend around 90% of their time indoors. Whilst severe pollution episodes from eg. open fires are relatively rare in developed countries, concerns remain as new buildings, paints, furniture and a variety of household products are sources of indoor VOC. Many important indoor VOC are known (from previous outdoor studies) to degrade into more harmful products such as formaldehyde and acetaldehyde[2,3]. However, several important and unique features of indoor air make any inferences based on outdoor air chemistry highly uncertain. First, indoor air is lacking in UV light required to generate free-radical oxidants such as OH; these radicals initiate the bulk of VOC oxidation outdoors. Second, a large surface-area to volume ratio is available indoors, promoting rapid loss of partially oxidised VOC products by dry deposition. Third, indoor air is invariably humid, and H2O is known to enhance rates and yields of many VOC oxidation reactions.

Figure 1- many factors influence indoor air, including dust, pets, damp, household chemicals, cooking, outdoor air, smoking & houseplants.

Accordingly, experiments in this project will be carried out both in the built environment (homes, offices) and in controlled laboratory conditions, to determine removal rates and key product yields for indoor VOC. Focus will be given to oxidation of limonene (1-Methyl-4-(1-methylethenyl)-cyclohexene, see Fig. 2), as the presence of this unsaturated VOC indoors has been linked to elevated levels of the formaldehyde [2,4] (toxic, a human carcinogen, respiratory irritant and allergenic). Limonene is a major fragrance component of household and personal hygiene products, and is increasingly used in food manufacturing, medicines and as a solvent for cleaning, paints / paint-stripper, glues and 3D-printing. A critical parameter required to understand the role of any indoor VOC is its lifetime. For unsaturated VOC such as limonene this will be a controlled by the efficiency of ventilation, and by removal in chemical reactions such as with O3, and potentially any trace quantities of highly reactive radicals such as OH and NO3. Removal rates may be measured directly by monitoring the time taken to return to equilibrium levels following controlled release of a VOC.

Figure 2 - Limonene, a naturally occurring VOC with a clean citrus odour is a common component of household products and many industrial applications.

Experimental methods will include a variety of atmospheric analytical techniques, notably direct monitoring of VOC (and VOC oxidation products) by chemical ionisation mass-spectrometry. These techniques will be coupled to gas-phase kinetic methods for determination of removal rates and product yields both in the lab and in a variety of indoor test locations.

The science from this project will make an important contribution to understanding indoor air pollution, but it will also help industry develop better performing products. With improved knowledge of VOC lifetimes, there is potential for designing delivery and formulations that maximise perceived performance for users, whilst minimising chemical usage and any potential for formation of more harmful by-products.  The project will be a CASE award with support and co-design by Givaudan UK, part of the world’s largest fragrance manufacturing company.


In this project, you will work with leading atmospheric scientists from the Wolfson Atmospheric Chemistry Laboratories in York, and at Givaudan UK (Ashford, Kent) to investigate the rates and products of VOC oxidation indoors. In particular, according to your particular research interests, the studentship could involve:

  1. Experiments to measure indoor lifetimes of limonene and other VOC for the first time.
  2. Direct quantitative measurements of limonene and other important VOC concentrations in a variety of indoor test locations (homes, offices, industry).
  3. Direct quantitative indoor measurements of VOC oxidation products, notably formaldehyde.
  4. High-precision laboratory-based measurements of rates and products of VOC oxidation reactions in realistic indoor air conditions of temperature, pressure and humidity.
  5. Modifications of atmospheric oxidation models 3 for use with indoor air.

Potential for high impact outcome

Indoor air quality and impacts on human health are among the most pressing issues facing Western society. We are in a unique position in York to tackle important unresolved questions about how VOC chemistry. The research will have immediate science, health and industrial-policy related impacts, and we anticipate results being suitable for publication in high impact journals. The collaboration with Givaudan provides a route for science to find its way rapidly into real-world applications and business. 


You will work under the supervision of Dr. Terry Dillon and Prof. Ally Lewis in the Wolfson Atmospheric Chemistry Laboratories (WACL), part of the University of York Department of Chemistry (YDC). WACL is a new facility bringing together experts in atmospheric measurement techniques, Earth system modelling and laboratory-based measurement to form the largest and best-integrated atmospheric science team in the UK. Dr Dillon has a wealth of experience in the study of VOC oxidation reactions, mechanisms and products, and will provide training in all kinetic methods to be used here. Prof. Lewis is an expert in VOC measurements using a wide variety of techniques, platforms and in many terrestrial environments; Prof. Lewis and the WACL team will provide comprehensive training in the analytical instrumentation required for the indoor air measurements.

This project provides a high level of specialist scientific training in: (i) State-of-the-art analytical techniques for trace gas monitoring; (ii) perturbation techniques for kinetic measurements; (iii) development and use of detailed chemical mechanisms for computer model simulations. Co-supervision will involve regular meetings between all partners and extended visits to Ashford, Kent, where they will work alongside researchers in Givaudan. This studentship is offered as part of the SPHERES Doctoral Training Programme that will provide training in addition to that offered by YDC.  Courses are specifically aimed at aiding your development throughout your PhD, improving transferable skills, putting research into a wider scientific context and preparing you for thesis presentation and viva.

Student profile

You should have a strong background in the physical sciences (physics, chemistry or similar) and a keen interest in environmental issues. We appreciate that this PhD project encompasses several different science and technology areas. Whilst an aptitude and enthusiasm for experimental work is desired, the WACL team is very well supported with experienced scientists. Training in new techniques and disciplines is all part of the PhD, and no previous experience with any specific techniques or instruments is necessary.

CASE Partner

The proposal has been agreed as a “Partnership Project” (a potential CASE project) with Givaudan providing extra funding additional to the NERC student stipend. The project aligns with a long-standing collaboration between WACL at York and Givaudan UK on the science and technology of VOCs and their measurements.


  3. Weschler, C. J. (2011) Indoor Air, 21: 205–218. 

Related undergraduate subjects:

  • Chemistry
  • Physical science
  • Physics