AIR QUALITY MONITORING ON THE LONDON UNDERGROUND: DEVELOPING NEW UNDERSTANDING OF PARTICULATE MATTER VARIABILITY AND SUPPORTING MITIGATION STRATEGIES

Air pollution is the largest environmental health risk of the 21st century due to its detrimental health impacts, and disproportionate impacts on people living in urban areas as a result of heightened anthropogenic activities. Particulate matter (PM) is often viewed as the most dangerous pollutant, as it is made up of a heterogenic mixture of microscopic particles (<10 micrometres in diameter), is inhalable, and can pass through the lungs into the bloodstream.
In London, an estimated 4,000-9,000 Londoners die prematurely due to air pollution exposure annually, with associated economic costs of around £1.4 to £3.8 billion yearly Recent developments have seen the traditional air quality measurement networks (e.g. LAQN) being successfully extended by lower-cost sensors (e.g. Breathe London), however, many under-monitored microenvironments within London remain. One such environment is the London Underground (LU), with 88 million journeys a month. On the LU, particulate matter (PM1.0, PM2.5, PM10) is the most prevalent pollutant, often reaching concentrations 100 times higher than annual mean concentration guidelines.
Despite this, the system remains largely understudied. Currently, very little is known about the seasonal or long-term variability of PM in the system, the contribution of different sources to overall PM concentrations, the role of ambient meteorology and seasonal cycles, or the effectiveness of cleaning regimes conducted by Transport for London. These uncertainties continue to impact Londoners daily, and are vital to examine in order to build a healthier city.
This PhD project will address these uncertainties by developing a range of low-cost air quality sensors to be deployed simultaneously across multiple stations in the system, both on identified platforms and station entrances. This will allow for long-term (> 1 year) monitoring of PM concentrations, source-differentiation using PM size bin number concentrations, modelling of dispersion within the system, and evaluation of ongoing cleaning regimes and filtration units to be installed by TfL as a management option for PM within the LU. Source differentiation will be supported by collecting dust samples within the LU that will be analysed in the QMUL labs by ICP-MS.

These approaches will lead to new insights on the seasonal cycle of pollution on the LU, the impact of above ground meteorology on pollutant concentrations, allow for mitigation measures to be proposed, and inform policy makers to initiate discussions around the introduction of indoor air quality guidelines.