Characteristics and source apportionment of PM ₁ emissions at a roadside station

The mass concentrations of PM ₁ (particles less than 1.0μm in aerodynamic diameter), organic carbon (OC), elemental carbon (EC), water-soluble ions, and up to 25 elements were reported for 24h aerosol samples collected every sixth day at a roadside sampling station in Hong Kong from October 2004 to September 2005. Annual average PM ₁ mass concentration was 44.5±19.5μgm ^-3. EC, OM (organic matter, OC×1.2), and SO ₄ ⁼ were the dominant components, accounting for ∼36%, ∼26%, and ∼24% of PM ₁, respectively. Other components, i.e., NO ₃ ^-, NH ₄ ⁺, geological material, trace elements and unidentified material, comprised the remaining ∼14%. Annual average OC/EC ratio (0.6±0.3) was low, indicating that primary vehicle exhaust was the major source of carbonaceous aerosols. The seasonal variations of pollutants were due to gas-particle partitioning processes or a change in air mass rather than secondary aerosol produced locally. Vehicle exhaust, secondary aerosols, and waste incinerator/biomass burning were dominant air pollution sources, accounting for ∼38%, ∼22% and ∼16% of PM ₁, respectively. Pollution episodes during summer (May-August) which were frequently accompanied by tropical storms or typhoons were dominated by vehicle emissions. During winter (November-February) pollution episodes coincided with northeasterly monsoons were characterized by secondary aerosols and incinerator/biomass burning emissions.