Yisi Liu

Project title: Using sensors to investigate the acute effect of traffic-related air pollution in different commuting modes

Degree: PhD | Program: Environmental and Occupational Hygiene (EOHY) | Project type: Thesis/Dissertation
Completed in: 2021 | Faculty advisor: Edmund Y. W. Seto


The contribution of transportation to ambient particulate matter (PM) has increased since 2000 in China. Over this time, Chinese cities have grown rapidly in size, population, car ownership and daily commute distance. These changes have led to increased travel times, exposures to traffic-related air pollution (TRAP) and combined uses of transportation modes during daily commutes. This dissertation aims to explore the health impacts of TRAP exposure for different commuting modes, evaluate a possible intervention to mitigate the adverse effects of TRAP in traffic, and investigate the relationships between built environment factors and travel behaviors for adults in Chengdu, China. First, portable sensors were employed to characterize TRAP and noise exposures in different transportation modes, neighborhoods and seasons in Chengdu. The study found that car trips exposed people to the lowest TRAP and noise levels compared to other modes (i.e., cycling, riding buses, and riding subways). Second, a randomized double-blind crossover intervention experiment was conducted among 21 healthy adults, where each subject travelled on a scripted route repeatedly for two hours using different transportation modes. Subjects used portable positive pressure respirators in half of the trips and wore sham respirators in the other half of the trip. TRAP exposure was recorded during each trip and cardiorespiratory health outcomes were measured immediately before and after trips. The study showed traveling by bus, subway or walking was associated with increased heart rate and decreased lung function as compared to riding in a personal motor vehicle. Increased black carbon and PM with aerodynamic diameter less than 1.0 μm (PM1) exposures were associated with elevated airway inflammation and decreased lung function, respectively. However, the study found no significant differences in cardiorespiratory health outcomes between subjects wearing effective respirators and those using sham respirators for two hours in traffic. Third, a commute survey was conducted in Chengdu to ask for home addresses, work locations and time respondents spent in multi-modal commuting. The non-linear relationships between built environment factors extracted from a Geographic Information System and time spent in different transportation modes were explored. Finally, a health impact assessment was performed for TRAP exposure and physical activity to evaluate the impact of multi-modal commuting under potential built environment changes on cardiovascular diseases mortality for employed urban residents in Chengdu. The study found that home-work distance was the most important factor in determining time spent in different travel modes. The health impact assessment showed that generally, commuting under the policy of garden city and easier access to public transit would be beneficial for cardiovascular health of residents. However, a longer home-work distance was estimated to lead to excess cardiovascular diseases mortality due to increased TRAP exposure and reduced physical active in daily commutes. Overall, these studies in Chengdu, China suggest that active and public transportation exposes commuters to higher TRAP levels. For interventions at the individual level, wearing a novel positive pressure respirator to reduce TRAP exposure during commutes may not improve the cardiorespiratory health among healthy adults. For policy interventions, the planning policy of garden city and TOD would potentially benefit population health for employed urban residents in Chengdu. However, future planning policies are needed to reduce pollutant concentrations and to address the job-housing mismatch in Chinese cities to reduce commuting distances and to protect population health.

URI: http://hdl.handle.net/1773/47478