Aroma chemicals and their impact on indoor air quality

This project will deploy experimental, modelling and measurement expertise to enhance our knowledge of reactive aroma chemicals (AC) and minimise impacts on indoor air pollution. You will determine rates for the most important AC reactions indoors, measure yields of the most harmful products and assess impacts using model simulations. Together with project partners. you will design and test novel environmentally friendly AC formulations for common household products. Sources of indoor air pollution (IAP) include ingress of outdoor air, emissions from building materials and furnishings, household plants / mould and activities such as cooking, cleaning and use of personal care products. We spend 90% of our time indoors, largely in homes and workplaces. Consequently, even pre-pandemic, our exposure to air pollution was almost exclusively indoors. Activities such as cleaning and use of personal care products generate high pollutant concentrations as, in addition to active ingredients, products are routinely dosed with AC to make them attractive to consumers. Increasing disposable income in developing regions and consequent product use is fuelling demand for AC, the market for which is projected to surpass $8bn by 2027. Toxicity, eye / skin irritation and aqueous-phase environmental degradation are assessed when formulating AC mixtures. However, the gas-phase breakdown of AC and consequent impact on indoor pollution has been largely neglected, with regulations focused on occupational exposure.

Inexpensive and sTerpenes in cleaning products lead to indoor air pollutionustainably sourced, monoterpenes (C10H16) are attractive AC for consumer products, including those marketed as “natural” or “chemical-free”. Limonene (Fig. 1) has a “clean citrus” aroma and is widely used in washing-up liquid, air-freshener and candles. “Pine-fresh” alpha-pinene is used in disinfectant, bathroom- and floor-cleaners. Limonene and alpha-pinene are of low-toxicity, but react rapidly with atmospheric oxidants (OH and O3); subsequent breakdown in air produces a host of secondary pollutants including the carcinogen formaldehyde (HCHO). Limonene and alpha-pinene are among the most reactive monoterpenes and therefore represent an avoidable pollution source and serious health concern. Alternative AC are available, with some in widespread use. However, we simply do not know if they are less reactive as we lack the rate-coefficient or product yield data from which to make an informed assessment. In this project, we will target a variety of AC from the popular fragrance categories of floral, citrus, woody and fruity. These AC molecules span the most common chemical classes of alkenes alcohols, ethers and esters which together make up > 50% of the AC market. You will determine rates of AC breakdown and measure yields for the most harmful products. Techniques will include use of both pulsed laser photolysis and relative rate for kinetic studies, indoor air chambers for product yields, and the INDCHEM-py model for impact assessment. The improved understanding of AC gained in this project will be used to design and test novel environmentally-friendly formulations for household products and so minimise AC impact on indoor air pollution.

You will work under the supervision of Dr. Terry Dillon and Prof. Nic Carslaw at University of York. You will be based in the Wolfson Atmospheric Chemistry Laboratories (WACL), a unique facility bringing together experts in atmospheric measurements, Earth system models and laboratory chemistry to form the largest integrated UK atmospheric research team. You will develop transferrable skills in the design and performing of kinetic experiments, spectrometric characterisations (e.g., Chemical Ionisation Mass-Spec.), chemical mechanism development and in data evaluation and model analysis. The University of York and the wider PANORAMA DTP provide comprehensive training programmes for students throughout their PhD studies, with a range of courses on both hard and soft skills, e.g. improving transferable skills, putting research into a wider scientific context and preparing for thesis presentations and viva.

Student profile – you will have a strong scientific background (good degree in chemistry, physics, natural or environmental science or similar), a keen interest in environmental issues, and an aptitude and enthusiasm for experimental work. We appreciate that this project is highly interdisciplinary and encompasses several different science and technology areas. However the York team is well supported with experienced scientists and technical support; all training will be provided, and no previous experience with specific techniques or instruments is necessary.