Characteristics of the Berner Impactor for Sampling Inorganic Ions

Abstract

The Berner cascade impactor was studied extensively to validate a method for measuring the sue distributions of inorganic ionic chemicals in ambient air. Stage efficiencies were calibrated from 0.06-to 10-pm particle diameters; the monodisperse submicron test aerosol was solid ammonium fluorescein coated with oleic acid. Sampled alone, laboratory-generated liquid aerosol suffers blowoff from the last two stages, but this effect is absent with ambient aerosol. Stage cutoffs are sharp and wall losses small. A fluorocarbon grease compatible with acid and ion analysis was shown to prevent particle bounce effectively. Ammonium sulfate particles are sized properly at high relative humidity, ruling out possible growth by condensation during jet expansion. The volatilization loss of submicron ammonium nitrate particles is less than 10% under conditions that produce up to 95% loss from Teflon filters. On the basis of loading experiments, this result is ascribed mainly to the small surface-to-mass ratio of the deposits. A data inversion program was developed, based on a Smooth-Twomey algorithm by Markowski. An example of the size distribution of the principal inorganic ions in ambient air is presented.

A Field Intercomparison of Three Cascade Impactors

“…Due to the low-pressure design, humidity effects might distort size distributions. Wang and John (1988) concluded that size changes were negligible at up to 70% RH for stages with size cuts of 0.075 pm and larger, but humidities are often above that in the marine boundary layer. The same study reported low internal losses for this design.…”

“…The last stages collect those particles by operating at low pressure, thus reducing the amount of air available to deflect the particles away from the impaction surface. Several calibrations have been performed on various versions of the Berner impactor (Wang and John, 1988;Hillamo and Kauppinen, 1991). Due to the low-pressure design, humidity effects might distort size distributions.…”

“…1. They are derived from stage collection efficiency and internal loss data (Willeke, 1975 for the Sierra; Wang andJohn, 1988 andHillamo andKauppinen, 1991 for the for the MOUDI). The MOUDI has the sharpest size cuts, minimizing cross-sensitivity between stages.…”

A high-flow humidograph for testing the water uptake by ambient aerosol

“…For dry aerosol the above-mentioned increase in RH does not give rise to an increase in size. Wang and John (1988) showed that in Berner low-pressure impactors such a projected increase in size was not signi"cant. However at the rather low RH used in that study (69%), the aerodynamic size of the aerosol is not very sensitive to an increase in humidity.…”

Design and Testing of the NCTU Micro-Orifice Cascade Impactor (NMCI) for the Measurement of Nanoparticle Size Distributions

“…Commercial cascade impactors with the cutoff aerodynamic diameter (d pa50 ) covering the nanosize range include the micro-orifice uniform deposit impactor (MOUDI) (MSP Corp., Shoreview, MN, USA; Marple et al 1991), the quartz crystal microbalance (QCM) cascade impactor (California Measurements, Inc., Sierra Madre, CA, USA ;Chaun 1970), and the electric low-pressure impactor (ELPI) (Dekati Ltd.; Keskinen et al 1992). The Berner lowpressure impactor could also collect particles of very small sizes at the lower stages (Berner et al 1979;Wang and John 1988). Extensive studies have been devoted to resolve the three major problems which may distort the size distributions when using cascade impactors.…”