Size distribution of organic and inorganic species in Hong Kong aerosols during the wet and dry seasons

Organic compounds including alkanes, fatty acids, and polycyclic aromatic hydrocarbons (PAHs) and trace and major elements in four size fractions (<0.49 μ m, 0.49–0.95 μ m, 0.95–2.5 μ m, and 2.5–10 μ m) collected from June 1998 to January 1999 in Hong Kong were physically and chemically characterized by scanning electron microscope (SEM), gas chromatography/mass spectrometry (GC‐MS), and inductively coupled plasma/mass spectrometry (ICP‐MS) to study their size distributions, seasonal variations, and sources. SEM micrographs show that abundances and shapes of particles in each size fraction exhibit distinct difference between wet and dry seasons. Solvent extractable organic compounds (SEOC) investigated in this study were significantly enriched in fine particulate matter (PM2.5) since 97% of PAH, 88% of alkane, and 69% of fatty acids in PM10 were actually from PM2.5. The pollution elements and SEOC showed a change from a maxima in the finest fraction (<0.49 μ m) in the wet season, to an obvious increase in the 0.49–2.5 μ m fraction in September and October, and to a maxima in the finest fraction again in November and December. This corresponds to a change from a strong local emission from pollution sources, to possibly aged materials in the transition period of Asian monsoon, and to the pollution emissions dominated by those transported from the continent. The distinct difference of particle size distributions between wet and dry seasons suggests that the health effects of particles in Hong Kong may be different in those seasons.