Short-term and long-term exposure to fine particulate constituents and related health effects in Hong Kong

Abstract

Numerous epidemiological studies have reported fine particular matter (PM2.5) was associated with cardiopulmonary morbidity and mortality. However, such associations varied by time and region. One explanation is that the chemical constituents of PM2.5 vary across seasons and locations. Therefore, it is essential to identify the relatively harmful constituents of PM2.5 for providing evidence to establish air pollution standards and control strategy, as well as allowing us to better understand the underlying biological mechanism of the relevant health impacts. The concentrations of air pollutants in Hong Kong are relatively higher compared to most North American and European cities, with different exposure and composition patterns. A number of studies have been conducted to investigate the acute health impacts of particulate constituents. However, the routine measurement networks for PM2.5 constituents were only available every three or six days. The current thesis work made use of the Monitor for AeRosols and Gases in ambient air (MARGA) measurements, a semi-continuous monitoring system providing higher temporal resolution measurements than the traditional filter pack. Time series analysis was utilized to investigate the associations between short-term exposure to fine particulate matter, its constituents as well as major gas pollutants and cause-specific hospital admissions. Robust associations were observed for cardiovascular hospitalizations with nitrate and respiratory hospitalizations with sulfate and potassium.

Furthermore, few study has been conducted regarding chronic health impacts of specific fine particulate constituents in Asia. This thesis work took advantage of an elderly cohort in Hong Kong to assess the long-term exposure to PM2.5, black carbon (BC) and nitric dioxide (NO2) and the cardio-respiratory mortality based on high spatial resolution air pollutants data derived from a newly developed land use regression (LUR) model for Hong Kong. The current study demonstrated that the mortality of natural cause and cardiovascular diseases, but not for respiratory diseases, were significantly in association with PM2.5 [1.03 (95%CI: 1.01, 1.06) for natural cause; 1.06 (95%CI: 1.02, 1.10) for cardiovascular cause] and BC [1.03 (95%CI: 1.00, 1.05) for natural cause; 1.07 (95%CI: 1.02, 1.11) for cardiovascular cause] in a long time frame among an elderly population in Hong Kong. Significant associations were not observed for NO2 with either cardiovascular or respiratory diseases.

This thesis work investigated health effects of PM2.5 and its constituents in both short- and long-term time frames, which marked an important addition to research on PM2.5-relevent health impacts. The current study suggests that it is an effective way to inform air pollution standards or control strategies by regulating targeted sources of PM2.5 constituents, complementary to the current strategies targeting PM2.5 mass.