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

Abstract

The mass concentrations of PM 1 (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 PM 1 mass concentration was 44.5 ± 19.5 μg m −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.