Wide Range Aerosol Classifier: A Size Selective Sampler for Large Particles

Abstract

The Wide Range Aerosol Classifier (WRAC), a sampler employing parallel impactors coupled with a large high flow rate inlet, has been designed, built, and tested for use in determining the size distribution of large particles found in ambient air. Results of laboratory and field evaluations demonstrate that the WRAC can be used successfully to determine atmospheric aerosol “total mass” and its large particle (> 10 μm aerodynamic diameter) distribution. The sampler is mobile for operation at various field locations. With properly prepared impaction surfaces, four impactors with cut points of 9.3, 18.5, 34, and 47 μm, respectively, provide sharp well-defined separation with low internal losses. Results of an initial and two follow-up independent impactor calibrations are in strong agreement, indicating good impactor precision and valid procedures by the two calibration laboratories. The WRAC size distribution mass measurements can be used to predict the “total aerosol mass” as well as size fractionated mass such as PM₁₀. The size distribution data are useful in evaluating the size separation characteristics of PM₁₀ and other size-selective particulate mass samplers. Successful field measurements have shown ambient aerosol distribution to display a large particle mode containing significant mass under a variety of conditions throughout the United States.