Characteristics and source apportionment of PM1 emissions at a roadside station

Highlights: → We present results from 24 h roadside measurements of PM1 mass and main components. → Elemental carbon, organic matter, and sulfate are the dominant components. → All elements related to human health are lower than the guideline values. → Vehicle exhaust episodes occur during summer. → Secondary aerosols and incinerator/biomass burning episodes exist during winter. - Abstract: The mass concentrations of PM1 (particles less than 1.0 μm in aerodynamic diameter), organic carbon (OC), elemental carbon (EC), water-soluble ions, and up to 25 elements were reported for 24 h aerosol samples collected every sixth day at a roadside sampling station in Hong Kong from October 2004 to September 2005. Annual average PM1 mass concentration was 44.5 ± 19.5 μg m-3. EC, OM (organic matter, OC x 1.2), and SO4= were the dominant components, accounting for ∼36%, ∼26%, and ∼24% of PM1, respectively. Other components, i.e., NO3-, NH4+, 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 PM1, 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.