Project No: 11204115

Title: Semi-volatile particulate matter (PM) species in roadside environment: Role in gas-particle partitioning and formation of oxidative potential

PI: Prof. Ning, Zhi    CI: Prof. Zoran, Ristovski

Deteriorating roadside air quality, particularly in metropolitan cities like Hong Kong, has raised significant concern for the adverse impact on public health. Numerous epidemiological studies, including those conducted in Hong Kong, have demonstrated strong associations between exposure to fine particulate matter (PM2.5, dp<2.5μm) and increased mortality. The World Health Organisation (WHO) recently also classified diesel exhaust as a ‘definite carcinogen’ with an increased risk of lung cancer. However, the exact underlying mechanisms by which PM cause adverse health effects are still largely unknown, due to the lack of understanding on the complexity of particles and how they evolve from source to exposure. The key subject is the semi-volatile PM components that play vital roles in the dynamic evolution of PM physical, chemical and toxicity properties, given the fact that some of the components are carcinogenic themselves.

The objectives of the project are to understand the role of semi-volatile PM components in changing particle size, morphology and chemical composition in roadside environment that largely affect the pedestrian exposure, and to determine how the environmental conditions, such as temperature and relative humidity, affect the interaction of semi-volatile components and particles. Also we will investigate the contribution of semi-volatile PM species to the formation of reactive oxygen species leading to PM toxicity.

The proposed study will carry out field investigation in diesel emission dominant near-source and urban ambient environments with varying and controlled experimental conditions to understand the behavior of semi-volatile PM species in the new particle formation, condensation and ageing or secondary formation processes. Microphysical and chemical analysis on the size-segregated and time-integrated samples will be performed and compared to provide the insight into the role of semi-volatile species in causing the particle toxicity, which will be evaluated by determining the formation of PM-induced reactive oxygen species (ROS). A novel online ROS measurement method will be developed from modification and refinement of a well-established ROS probe by the investigators. A total of 8 weeks sampling campaign, 4 in summer and 4 in winter, is planned to cover both diurnal and seasonal variation of the environmental conditions. 24 hours continuous sampling will be dedicated each day to capture the aerosol diurnal pattern of chemical and ROS concentrations for statistical analysis on their relationship to determine the surrogates of particle toxicity.

The results from the project will clarify the role of semi-volatile species in driving the dynamic evolution of vehicular exhaust PM and provide an insight of the underlying mechanisms by which semi-volatile PM components affect the pedestrian roadside exposure. Success of the project will address the key issues on the protection of public health in the urban population exposure to roadside pollutants and in well-informed and effective air policy and emission control strategy formulation.