Characterization of the ARM Aerial Facility optically based aerosol instrumentation

Description

The ARM Aerial Facility (AAF) faces unique challenges when measuring aerosol physical properties. The DOE AAF G-1 does most sampling at speeds around 100 m/s. At this flight speed, sampling rates of 1 Hz or greater are required to acquire measurements with adequate spatial resolution of the in situ aerosol. Optically based measurement techniques comprise the most common basis to meet this need. AAF operates an ultra high sensitivity aerosol spectrometer–airborne (UHSAS), passive cavity aerosol spectrometer (PCASP), and a cloud aerosol spectrometer (CAS) to make high-speed measurements of aerosol size distributions from 0.06 to 10 μm. However, the use of these instruments can lead to difficulty in the accurate sizing of the aerosol. The shape and chemistry changes the index of refraction of the particles, which shifts the measured size of the aerosol away from its actual size. If the shift is not quantified, optical closure studies or cloud condensation nuclei closure studies will have unknown errors and inaccurate results.

AAF is utilizing state-of-the-art facilities and instrumentation, available at the Atmospheric Measurements Laboratory at the DOE Pacific Northwest National Laboratory, to characterize the aforementioned instruments. With future field campaigns planned within biomass burning (BioBurns) and in heavily organic environments (GoAmazon), it is imperative that the instruments are fully tested with representative aerosol from these environments. An overview of the testing methodology, preliminary lab results, and preliminary results from the Two-Column Aerosol Project (TCAP) will be presented.