Abstract Number: 844 Working Group: Instrumentation and Methods
Abstract The new ice-impacting (icePAC) Exhaled Breath Aerosol Collector (EBAc) was developed for efficient collection of particles and proteins exhaled by a subject person. The EBAc takes advantage of the vapor-saturated nature of the exhale breath to enable condensational growth and concentrated collection of particles down to 10nm onto an ice substrate. Exhaled breath flows through six wick-lined parallel tubes maintained at 0oC, subsequently passing through a delivery nozzle, and impinges onto a sample collection plate maintained at approximately -14oC. Enlarged particles are deposited by impaction onto an ice-covered surface. The cold tubes serve two purposes: 1) due to the non-linearity of the water vapor pressure curve, water condenses on particles in the exhaled breath causing them to grow above 1 micrometer allowing collection by impaction; and 2) removal of the water vapor condensed on the wick walls, concentrating the collected sample. The new EBAc was tested in the laboratory using test aerosols to optimize sampling conditions for highest collection efficiency. Relative humidity of the incoming flow, particle size and sampling time were some of the parameters evaluated. Collection efficiency was highly dependent on the RH of the sampling aerosol. Low efficiencies were measured for RH <75%, increasing rapidly with increasing RH, and reaching 85-90% at RH=85%. At RH=90% both ambient and sulfate particles were collected with efficiencies higher than 95%. For particle size dependency, collection efficiencies higher than 90% were measured for particles Dp>10nm, decreasing to ~80% for particles down to 8 nm.
Collection efficiency under optimized conditions was also tested by chemical analysis. Results for the EBAc compared with a sequential spot sampler suggested that loses into the delivery nozzle were minimal, with high collection efficiencies onto the ice collection surface. In summary, the collection efficiency of the EBAc is about 90% when considering both physical and chemical collections.