Development of polydisperse aerosol generation and measurement procedures for wind tunnel evaluation of size-selective aerosol samplers

Abstract

Accurate development and evaluation of inlets for representatively collecting ambient particulate matter typically involves use of monodisperse particles in aerosol wind tunnels. However, the resource requirements of using monodisperse aerosols for inlet evaluation creates the need for more rapid and less-expensive techniques to enable determination of size-selective performance in aerosol wind tunnels. The goal of recent wind tunnel research at the U.S. EPA was to develop and validate the use of polydisperse aerosols which provide more rapid, less resource-intensive test results which still meet data quality requirements necessary for developing and evaluating ambient aerosol inlets. This goal was successfully achieved through comprehensive efforts regarding polydisperse aerosol generation, dispersion, collection, extraction, and analysis over a wide range of aerodynamic particle sizes. Using proper experimental techniques, a sampler's complete size-selective efficiency curve can be estimated with polydisperse aerosols in a single test, as opposed to the use of monodisperse aerosols which require conducting multiple tests using several different particle sizes. While this polydisperse aerosol technique is not proposed as a regulatory substitute for use of monodisperse aerosols, the use of polydisperse aerosols is advantageous during an inlet's development where variables of sampling flow rate and inlet geometry are often iteratively evaluated before a final inlet design can be successfully achieved. Complete Standard Operating Procedures for the generation, collection, and analysis of polydisperse calibration aerosols are available from EPA as downloadable files. The described experimental methods will be of value to other researchers during development of ambient sampling inlets and size-selective evaluation of the inlets in aerosol wind tunnels.