A Particle-into-Liquid Collector for Rapid Measurement of Aerosol Bulk Chemical Composition

Abstract

We report on a new instrument developed for rapid automated on-line and continuous measurement of ambient aerosol bulk composition. The general approach is based on earlier devices (Khlystov et al. 1995; Simon and Dasgupta 1995) in which ambient particles are mixed with saturated water vapor to produce droplets easily collected by inertial techniques. The resulting liquid stream is analyzed with an ion chromatograph to quantitatively measure the bulk aerosol ionic components. In this instrument, a modi ed version of a particle size magni er (Okuyama et al. 1984) is employed to activate and grow particles comprising the ne aerosol mass. A single jet inertial impactor is used to collect the droplets onto a vertical glass plate that is continually washed with a constant water diluent ow of nominally 0.10 ml min ¡ 1. The ow is divided and then analyzed by a dual channel ion chromatograph. In its current form, 4.3 min integrated samples were measured every 7 min. The instrument provides bulk composition measurements with a detection limit of approximately 0.1 ¹g m ¡ 3 for chloride, nitrate, sulfate, sodium, ammonium, calcium, and potassium. Results obtained during its deployment in the August 1999 Atlanta EPA Supersite study are presented. BACKGROUND Process studies aimed at understanding sources, atmospheric transformation, and fate of ambient aerosols require knowledge of particle chemical composition. To date, quantitative composition measurements are typically performed off-line on particles collected onto substrates by ltration or inertial impaction. The collected sample is then manually extracted and analyzed. For example, measurements of ionic aerosol components involve collection on denuder-lter pack assemblies, extraction of the collected aerosol into water, and analysis of

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