Sampling and Characterization of PM- Fractions of Ambient Particulate Matter in Bangkok Utilizing a Cascade Virtual Impactor

Abstract

A cascade virtual impactor was developed and utilized for sampling and measurement of ambient aerosols in size classes demarcated by particle aerodynamic diameters of 10 m, 2.5 m and 1 m. Virtual impaction diminishes the flow of ambient air through the collected sample by 90%, consequently reducing the chance of sampling artifacts, such as extensive evaporation of semi-volatile compounds, or chemical cross-reactions after sample deposition. An omni-directional sampling head with an adjustable upper particle cut-off size was designed and numerically investigated for its suitability for PM sampling. The total flow rate through the instrument was 12.5 lpm; thus, with about five hours sampling, a total mass on the order of a few hundred micrograms in urban areas can be collected for air pollution determination purposes. Measurements were performed in Bangkok, Thailand to obtain mass concentrations, PAHs and carbon content of the sampled material. They show the feasibility of utilizing cascade virtual impaction for simultaneous sampling of various PM fractions and subsequent chemical analysis in air quality research and also give insight into the air pollution burden of this city.