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Edward E. Hindman
,
Lawrence F. Radke
, and
Mark W. Eltgroth

Abstract

Airborne measurements of cloud nuclei [cloud condensation nuclei (CCN) and ice nuclei (IN)] were made in the stabilized ground clouds resulting from the launches of a liquid-fueled ATLAS/Centaur rocket and a solid-fueled TITAN III rocket. Concentrations of CCN in both types of clouds were greater than ambient values for the ∼2 h duration of the measurements. The initial production of CCN active at 0.5% supersaturation in the ATLAS and TITAN clouds was equivalent to a 20 and 700 s emission, respectively, by the city of Denver, Colorado. Thereafter, the clouds continued to generate CCN at a rate of ∼1 cm−3 s−1. Concentrations of IN in the ATLAS cloud were greater than ambient values for only a short period after launch; the nuclei were probably from entrained launch pad and ground debris. The concentrations of IN in the TITAN cloud were mainly at or below ambient values (possibly due to the presence of high concentrations of HCI) until ∼2 h after launch when they increased substantially above ambient values. Estimates of the IN activity of the ground cloud material have large uncertainties due to unresolved discrepancies with previous laboratory measurements.

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Edward E. Hindman
,
Lawrence F. Radke
, and
Mark W. Eltgroth

Abstract

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Lawrence F. Radke
,
Peter V. Hobbs
, and
Mark W. Eltgroth

Abstract

Airborne measurements have been made of aerosol particle size distributions (>0.01 μm) in aged air masses, in the plumes from several coal power plants and a large Kraft paper mill, and in the emissions from a volcano, before and after rain or snow showers. These measurements have been used to deduce the precipitation scavenging collection efficiencies of aerosol particles ranging in size from ∼0.01 to 10 μm diameter.

Despite large variations in the nature of the aerosol particles and the precipitation, the scavenging collection efficiencies as a function of particle size showed marked similarities, with some well-defined maxima and minima values. The measurements agree well with theoretical calculations for aerosol particles >1 μm, but for the submicron aerosol particles the scavenging collection efficiencies are generally much higher, and the region of very low scavenging efficiencies (the “scavenging gap”) much narrower, than current theories predict. Some possible explanations for these discrepancies are suggested.

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