Status
Aerosols of size 0.05 µm to 5 µm are collected with Ames wire impactors. This instrument consists of 25 µm, 75 µm and 500 µm diameter palladium or gold wires on ring mounts exposed to air for up to 5 minutes. Smaller diameter wires utilize their higher collection efficiency for small particles. Alternately, the wires can be replaced by Formvar-coated glass rods to collect cloud particles of sizes up to 500 µm. The collectors are brought back to the laboratory for analysis of size, shape and elemental/chemical composition of the collected particles using optical and electron microscopy, energy-dispersive X-ray spectrometry and microchemical reaction spots on substrates sensitized with specific chemicals.
Improved time and space resolution of ice particle collections is achieved by simultaneous sampling with the continuous Formvar replicator. The prime utility of this instrument is to obtain direct measurements of ice and liquid (volatile) particle concentration, size (1µm D < 500µm) and shape over the period of approximately 2 hours per flight with a spatial resolution on the order of 20 m (at aircraft speed of 200 m/s). This opens the possibility of obtaining horizontal and vertical gradients of these quantities in cirrus clouds and contrails. Analysis of particles replicated on the films takes place by optical microscopy, interference microscopy and electron microscopy. The phases of supercooled or supersaturated solution droplets can be inferred from whether or not particles shatter or splash on impact to give sharp edged fragments or splash characteristics of high impact speed and high Langmuir numbers (high kinetic-to-surface surface energy ratios).