The four cylinders suspended below the Conquest's belly are particle probes, each of which has a different size opening to admit airborne particles of various sizes. When bits of smoke or ice crystals enter a probe, they pass through a laser beam. This causes the particle's shadow to be recorded inside the cylinder in digital form and then transmitted to an on-board computer where the information is stored. Particle probes allow scientists to observe some of the pollutants that are in a plume, but they are also essential in determining whether or not some pollutants may be responsible for localized precipitation. Pollutants Cause Snowfall in Winter Dr. Marianne English, a cloud physics specialist at Alberta Research Council, who is project manager for the plume tracking study, described one way that pollutants might interact with the atmosphere.
Pollutants can speed up or initiate normal precipitation processes.
You can get ice or water droplets to grow around them. On the other hand, if the plume comes into contact with clouds, the pollutants might be moved upward in the atmosphere or otherwise redistributed. Indeed, there is evidence that such phenomena are occurring. During a series of flights in cold, stable air in December 1983, the aircraft encountered ice crystals being formed immediately below the plume. I had decided to drop below the plume so I could fly directly back toward the stack when all of a sudden the particle probes encountered all sorts of ice crystals.