Identifying and evaluating interventions to reduce traffic-related air pollution exposure in professional driving occupations

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Personal exposure studies have found that individuals are exposed to the highest levels of traffic-related pollution while commuting. This is a concern as there is strong evidence that exposure to traffic-related air pollution, particularly diesel exhaust, has greater adverse health effects than pollutants from other sources. However, while people often spend one to two hours in the commuting environment each day, few studies have considered the exposures experienced by professional drivers who are required to drive in this environment for the majority of their working day. Due to the scarcity of studies and the likelihood that professional drivers are disproportionately exposed to traffic-related air pollution, a better understanding of how much pollution these drivers are exposed to and what can be done to reduce their exposure is needed. This thesis aimed to address this research gap by undertaking a comprehensive monitoring campaign to characterise professional drivers’ exposure to traffic-related pollution with a specific focus on diesel exhaust across a range of sectors. This exposure data were then analysed to identify the most important determinants of professional drivers’ exposure to develop realistic and cost-effective exposure reduction strategies based on real-world evidence.
The baseline monitoring campaign collected personal black carbon (BC) exposures as a proxy for diesel exhaust for 141 drivers across seven sectors in London. Each participant’s personal BC exposures were continuously measured using real-time monitors for 96 hours, incorporating four shifts per participant. Results found ‘at work’ BC exposures (median: 2.3 µg/m³) were 2.3 times higher compared to when participants were ‘not at work’ (1.0 µg/m³). Workers spent 19% of their time ‘at work driving’, however this activity contributed 36% of total BC exposure, highlighting the disproportionate effect that driving had on professional drivers’ daily exposure. Taxi drivers experienced the highest BC exposures at work due to the time they spent working in congested central London, while emergency services had the lowest, due to the reduced time spent driving during their shift. Spikes in exposure were observed while driving and were at times greater than 100 µg/m³. Further quantitative analysis and mixed effects models highlighted the most significant determinants of drivers’ BC exposures. These were driving in tunnels, the sector the driver worked in, congestion, driving on roads with higher numbers of buses and HGVs, window position, driving location, background BC concentrations, day of the week and time of day. Two further real-world intervention monitoring campaigns on a subset of 44 drivers were conducted investigating the effectiveness of portable in-cabin filters and reduced vehicle numbers on roads in reducing professional drivers’ exposure to traffic-related pollution. A further controlled test on 92 unique vehicles assessed the effect that vehicle type and ventilation settings had on in-cabin pollutant concentrations. Results of these campaigns found that setting ventilation settings to recirculate had the most immediate effect in reducing drivers’ exposures, although care needs to be taken when utilising this setting due to the accumulation of potentially adverse carbon dioxide levels from driver respiration. The in-cabin filter intervention only resulted in a slight reduction in exposure for drivers and therefore was not thought to be as effective as utilising the recirculate ventilation setting. The controlled test suggested that the filter quality built into vehicles’ ventilation systems likely resulted in differences in the infiltration of pollutants into the cabin, highlighting that different vehicle types could be important in reducing drivers’ exposure. The campaign which investigated the effect of reduced vehicle numbers during the COVID-19 lockdown suggested that potentially the most effective intervention to reduce exposures for professional drivers would be local or national policy to reduce the number of vehicles on roads.
The results of this thesis provide practical recommendations on interventions and strategies which drivers, employers, vehicle manufacturers and local policy makers can implement to reduce professional drivers’ exposure to traffic-related air pollution.
Date of Award1 Nov 2021
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorBenjamin Barratt (Supervisor) & Ian Mudway (Supervisor)

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