Simulating urban air pollution in the lab

This project aims at resolving airflow in and around buildings to better understand urban air pollution. According to the World Health Organization (WHO), 80% of people living in urban areas are exposed to unsafe levels of air pollution and with it an increased risk of heart disease, lung cancer, and respiratory disease. This research will study how pollution disperses in urban areas, in order to improve the pollution dispersion models used to make air quality forecasts and that inform urban planning and policy.

Experiments will be conducted on scale models in a controlled laboratory flow facility. The measured flow patterns can then be related to full-scale atmospheric flows, in the same way wind tunnel tests of scale models provide insights to vehicle aerodynamics. The majority of experiments will take place in a water flume facility and passive tracers will be released at key points around the model, as a surrogate for air pollution. The use of the water flume permits the use of advanced laser-based measurement tools that can capture full two-dimensional quantitative images of the dispersion process both at the fine scales near the pollution sources and at the city scale. This is the key feature that differentiates this work from previous wind tunnel and in-situ measurements of dispersion, which are typically limited to point measurements. The fellows is uniquely positioned to conduct these novel spatial measurements due to her expertise with the experimental techniques and her previous background analysing coherent structures and mixing in canonical turbulent shear flows. The University of Southampton is particularly suitable location for this research because of the combination of having a suitable water flume facility as well as the required high-resolution camera and laser systems.

This study is particularly timely as governments focus on improving environmental sustainability and air quality in cities. These results will improve our ability to inform local council and industry on how pollution disperses around the city, aiding them in making decisions impacting financial and environmental sustainability and public health and safety. In addition to these societal impacts, these results will have academic impact by improving meteorological models. Existing dispersion models focus on time-averaged predictions; however, these models struggle to predict spatio-temporal fluctuations and peak exposures, especially near the source. Understanding these dynamics is important for air quality, as even short term exposure to toxic gases and airborne particulate matter can have adverse health impacts. These results will improve our understanding of the underlying physics in order to guide theories and improve models for predicting the dynamics of pollution dispersion in complex urban regions.

The outcomes of this research will help to improve the air pollution models that scientists, building planners and politicians use to make informed decisions about air pollution. The improvement of these models promises to improve the health and well-being of the population by providing better tools to ensure environmental sustainability in the face of air pollution. The impact of these improvements will be supported through several routes described below:

(1) Engaging with policy makers and industry: Southampton has been named one of the most polluted cities in the UK. This is a major concern for the local city council, Defra, and local industry who strive for financial and environmental sustainability. This is also becoming a concern for the construction industry, who are facing pressure to conduct impact studies for new builds in urban areas. This research will support these end users by providing modelling data useful in developing policy and determining future strategic direction. To support this, the fellow is currently working with colleagues at the UoS who are setting up an air pollution sensor network with the Southampton City Council (Johnston et al. 2018). The results of these experiments will be essential for validating and making sense of the sensor data. Furthermore, preliminary work has also already opened a dialogue with the Associated British Ports (ABP), who are concerned with how their ship traffic impacts air pollution in Southampton. In the future, the fellow will also engage with construction companies such as RWDI and ARUP, who have ties with the UoS, and will build on our network by attending the MAGIC project meetings and the UK Fluids Network Special Interest Group on Urban Flows, which attract national industry and government agencies such as the Met Office and Public Health England.

(2) Engaging with National Defence users: The Defence Science and Technology Laboratory (Dstl) at Porton Down is concerned with understanding the hazard presented by airborne toxic materials in the environment. The data generated from these experiments is ideal for validating the results of their large-eddy simulation models. As a starting point for collaborations, Dstl previously co-supervised an undergraduate feasibility study with CV at Southampton, utilising the experimental methods developed in this project, which was an ideal proof of concept to lay the foundations for further collaborations using this experimental methodology to validate Dstl dispersion models. They are also happy to consult on the design and analysis of these experiments, providing guidance for the fellow and her PhD students.

(3) Outreach: Public engagement with research and related societal issues will also be promoted. One venue for engagement will be the new "Air Pollution Research Network" which was recently set up at the University of Southampton, which brings together modellers with people who will be ultimately using the model outputs, i.e. health scientists, city councillors, lawyers, industry representatives and the public. Another target for public outreach is to develop new exhibits for the university open days, which has in the past attracted over 6000 visitors of all ages. These activities are supported by and aligned with the University of Southampton's aims for research and innovation.