Aerosol mass spectrometer for aerosol characterization at the ambient aerosol test facility

One of the uses of the Ambient Aerosol Test Facility (AATF) at the U.S. Naval Research Laboratory is to operate as a test facility for developmental chemical aerosol sensors. The facility draws ambient air from outside the building, with or without HEPA filtration, then introduces aerosols by various means within a 30 cm diameter, 14 m long wind tunnel at flow velocities ranging from 2 to 20 m/s. The turbulent flow generated provides a uniform distribution to a few percent across 90% of the tube diameter to sampling ports in a 3 m long test section at the end. The test section allows sampling and analysis by various sensors to determine aerosol size, concentration, and chemical composition. For the current program of interest, we generate simulant aerosols representing various classes of chemicals of interest. A range of referee instruments to characterize the aerosol in terms of size, number and composition is planned. Commercially available particle sizers and counters, a gas analyzer and an aerosol mass spectrometer are part of the suite of referee instruments. We use a high-resolution, time-of-flight aerosol mass spectrometer (HR-ToF-AMS) from Aerodyne, Inc., which is configured with an aerosol focusing lens to transmit between 50 nm and 3.5 μm diameter particles, and provides size, mass loading and chemical composition information. A calibration system consisting of a scanning mobility particle sizer and a water-based condensation particle counter is used to validate the operation of the AMS instrument. We describe the AMS instrument and its use at the AATF for the assessment of other instruments.