Abstract

Particle Measuring Systems laser particle spectrometer (ASAS‐X and FSSP) probes were used to measure aerosol particle concentrations and size distributions during 11 out of 12 ER‐2 flights between Punta Arenas (53°S) and Antarctica (up to 72°S) from August 17 to September 22, 1987. The time resolution was 10 s, corresponding to a spatial resolution of 2 km. The data were divided into two size classes (0.05–0.25 and 0.53–5.5 μm radius) to separate the small particle from the coarse particle populations. Results show that the small particle concentrations are typical for a background aerosol during volcanic quiescence. This concentration is generally constant along a flight track; in only one instance did we measure a depletion of small particles during a polar stratospheric cloud (PSC) encounter, suggesting a nucleation of type I PSC particles on background aerosols. Temporary increases of the coarse particle concentrations indicated the presence of tenuous polar stratospheric clouds that were encountered most frequently at the southernmost portion of a flight track and when the aircraft descended to lower altitudes. During “particle events,” particle modes were found at 0.6 μm radius, corresponding to type I PSCs, and occasionally, a second mode at 2.0 μm radius, corresponding to type II PSCs.

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