Determinants of personal exposure to fine particulate matter (PM_2.5) in adult subjects in Hong Kong

Personal monitoring for fine particulate matter (PM _2.5) was conducted for adults (48 subjects, 18–63 years of age) in Hong Kong during the summer and winter of 2014–2015. All filters were analyzed for PM _2.5 mass and constituents (including carbonaceous aerosols, water-soluble ions, and elements). We found that season (p = 0.02) and occupation (p < 0.001) were significant factors affecting the strength of the personal-ambient PM _2.5 associations. We applied mixed-effects models to investigate the determinants of personal exposure to PM _2.5 mass and constituents, along with within- and between-individual variance components. Ambient PM _2.5 was the dominant predictor of (R ² = 0.12–0.59, p < 0.01) and the largest contributor (>37.3%) to personal exposures for PM _2.5 mass and most components. For all subjects, a one-unit (2.72 μg/m ³) increase in ambient PM _2.5 was associated with a 0.75 μg/m ³ (95% CI: 0.59–0.94 μg/m ³) increase in personal PM _2.5 exposure. The adjusted mixed-effects models included information extracted from individual's activity diaries as covariates. The results showed that season, occupation, time indoors at home, in transit, and cleaning were significant determinants for PM _2.5 components in personal exposure (R ² _β = 0.06–0.63, p < 0.05), contributing to 3.0–70.4% of the variability. For one-hour extra time spent at home, in transit, and cleaning an average increase of 1.7–3.6% (ammonium, sulfate, nitrate, sulfur), 2.7–12.3% (elemental carbon, ammonium, titanium, iron), and 8.7–19.4% (ammonium, magnesium ions, vanadium) in components of personal PM _2.5 were observed, respectively. In this research, the within-individual variance component dominated the total variability for all investigated exposure data except PM _2.5 and EC. Results from this study indicate that performing long-term personal monitoring is needed for examining the associations of mass and constituents of personal PM _2.5 with health outcomes in epidemiological studies by describing the impacts of individual-specific data on personal exposures.