Automatic Giant Nuclei Impactor

The Auto-GNI sampling is done using free-stream impaction (i.e., no inlet losses).  The exposed polycarbonate slides are stored and subsequently analyzed in EOL / RAF's GNI Microscope, an optical automated microscope with humidified air that allows for size determination using Kohler theory.  When flying in marine boundary layers, typically 50000 giant aerosol particles are sampled within a 10-s exposure time; this gives excellent size distributions over the measurement range in bins of 0.2 micron dry radius.  Longer sample times are possible for flight at higher altitude or otherwise in air with lower aerosol concentration.

Model: 1

Measurements Provided: Measurement of sea-salt aerosol particles with NaCl equivalent dry radius in the range 0.7 - 16 micron (coarse-mode aerosol particles).

Typical Sampling Rates: 1 slide exposure 10 seconds takes about 30 seconds, due to the robotics system. Up to 96 slides can be exposed per flight (3 cassettes, each with 32 slides).

Measurement Characteristics: Sea-salt particles, typically solution drops at relative humidity of more than 45%, are impacted on the polycarbonate microscope slides.

Calibration Methods: Sizing in the GNI microscope is verified by sizing glass beads of known size.

History of Significant Changes: EOL / RAF also has a manual GNI stick that allows for sampling from the C-130 only.  This manual GNI system requires an on-board full-time operator.  The AutoGNI system can be remotely controlled from the ground, using an operator that has a laptop with an internet connection.

DOI: https://doi.org/10.26023/r267-m386

Example(s) of Measurement: Jensen and Nugent (2017), J. Atmos. Sci., volume 74, pages 679 - 697.