Design of a Glass Impactor for an Annular Denuder/Filter Pack System

Abstract

A glass impactor for an annular denuder/filter pack system was developed, to further the application of denuder technology in sampling atmospheric gases and particles. The glass impactor consists of an entrance section containing the inlet tube, the acceleration jet, and the impaction plate, which is mounted at the entrance to the annular denuder. The impaction plate is a removable porous glass disk which can be impregnated with mineral oil to minimize bounce-off of the collected particles during sampling. Calibration tests showed that the impactor has a 50% aerodynamic particle cutoff size of 2.1 μm, at a flow of 10 L min⁻¹. Particle loss experiments were conducted. Total losses on surfaces inside the impactor, annular denuder, and filter pack, determined for particle sizes ranging between 1.50 and 2.77 μm, were lower than 3%. Co-located air sampling was conducted using the glass impactor and the Harvard impactor. Mass concentrations determined using the Harvard impactor were about 10% higher than for the glass impactor because the glass impactor has a slightly lower aerodynamic particle cutoff point, while sulfate concentrations obtained from the two systems were in excellent agreement.