Agents that could be used in chemical and biological warfare tend to disperse widely in the air when released. Quickly collecting a concentrated sample of these agents is critical to detecting them before they reach harmful dose levels in the air. Also, methods of detection such as by polymerase chain reaction are enhanced when the collected agents remain alive.
Other collection devices using wet cyclone designs are larger and heavier, have higher power demands, and are noisy, thereby precluding unobtrusive uses. Devices using impactors for collection do not maintain the viability of live agents.
The Aerosol-to-Liquid Particle Extraction System (ALPES) is a device that uses electrostatic precipitation to collect and concentrate airborne agents in a liquid sample for onsite or laboratory analysis.
The collection efficiency is 85% to 92%, depending on the size of the particles. The ALPES is designed to collect chemical agents; radioactive particles; micro-oganisms such as spores, bacteria, and fungi; and molecules and other substances associated with explosives.
The ALPES takes advantage of the long-proven use of wet electrostatic precipitation to separate particles from air. The device comprises an ionization section atop a tubular collection electrode enclosed in a column. A pump pulls air through the vertical column at a flow rate of up to 300 liters per minute. A reservoir at the bottom of the column contains liquid that is pumped up through the inside of the collection tube, which is charged at 8,000 volts. The liquid flows over the top of the charged tube and down the sides, collecting the ionized particles from the outside surface of the tube. The flow rate maintains a continuous film of liquid on the outer surface of the tube. Constant recirculation of the liquid through the tube concentrates the collected particles.
A valved sample loop enables diversion of the liquid to an online analyzer or to a sample vial for transport to a laboratory for analysis. With minimal pressure drop, the device consumes less than 12 watts of power and operates quietly. The recirculating liquid can be customized for specific situations. A buffered saline solution or a nutrient solution will maintain biological agents in a viable state, enabling faster and more accurate analysis.