The Aerosol Observing System Inlet Characterization Experiment

Description

The U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Climate Research Facility operates observation sites around the world for studying the properties of aerosols and clouds and their interaction with radiation, precipitation and the Earth’s surface. Measurements of aerosol properties are accomplished from Aerosol Observing System (AOS) platforms where ambient aerosol is sampled through an inlet stack and distributed to various instruments. Consequently, accurate measurements of these ambient aerosol properties depend critically on having accurate characterizations of the aerosol size-dependent transport losses from the entrance of the inlet stack to the inlet of each aerosol instrument. Such a measured characterization does not currently exist. To address this need, a series of experiments were performed that would provide a measured characterization of the size-dependent aerosol losses through the AOS inlet from the entrance to the exit of the inlet stack. Due to the physical dimensions and high sampling flow rate of the inlet stack, the ambient atmospheric aerosol was used as the aerosol source. The experimental approach for the inlet characterization involved measuring the ambient aerosol size distribution under two scenarios: [1] sampling directly from the ambient (outside the container), and [2] sampling from the exit of the inlet stack (inside the container). Experiments involved simultaneous sampling of scenarios [1] and [2], to account for the likely temporal variability in the ambient aerosol size distribution, and to allow for the extended sampling times needed to accumulate sufficient particle counts to mitigate the impact of potentially low aerosol concentrations. The instrumentation used to characterize the ambient aerosol size distribution included an SMPS (scanning mobility particle sizer, 10 – 500 nanometers), a UHSAS (ultra-high sensitivity aerosol spectrometer, 0.06 – 1 micron), and an APS (aerodynamic particle sizer, 0.5 – 20 microns). Implementation of this approach required two of each of the instruments listed above. The primary deliverables from this inlet characterization are size-dependent aerosol losses from the entrance to the exit of the inlet stack.