Once that problem was mastered, they were faced with another challenge. The aircraft travels forward at about 70 metres per second. Because it usually passes through the plume at right angles, the plane may be inside the plume only 10 or 15 seconds near the stack and perhaps 45 seconds at distances of 50 kilometres downwind. Conventional instruments that might have been used to analyze the samples being scooped up by the aircraft can only handle one sample every 20 to 40 seconds. At that rate, the aircraft could be in the plume and out again before the analyzer was ready for the next sample.
Pollutants can speed up or initiate normal precipitation processes.
You can get ice or water droplets to grow around them. We had to sacrifice some of the instruments' sensitivity to the substances they were analyzing, but it was either that or settle for very little useful data. Peake has found that sensitivity isn't all that important, however, because pollutant concentrations are high enough that analyzers have no trouble detecting them. So far, Peake has been able to observe reductions in the concentration of sulphur dioxide as it moves away from the stack, some of which is due to its conversion to particulate sulphate which can be collected on filters inside the aircraft. We also notice more sulphate is formed on the edges of the plume than on the inside.