Three-Dimensional Complete Cloud Condensation Nuclei Spectral Measurements

Most previous cloud condensation nuclei (CCN) measurements have been limited to supersaturations (S) above 0.1%. This means that S discrimination is confined to the Aitken size range (diameter < 0.1 um). However, the S range of the Desert Research Institute (DRI) CCN spectrometers extends down to 0.01%, which thus usually includes most of the Large Nuclei (LN) size range (0.1-1 um diameter). The S range needs this extension because: 1) many clouds form at S less than 0.1%; 2) LN may be precipitation embryos; 3) cloud droplet spectral width, which is important for precipitation, may depend on full CCN spectra; 4) concentrations of more massive (lower S nuclei) need to be considered for static CCN closure (comparisons of particle size and composition with CCN); 5) since the lower S nuclei condense the most water they need to be considered for dynamic CCN closure (comparisons of predicted cloud droplet concentrations from CCN and updraft with measured cloud droplet concentrations); 6) wide CCN spectra are needed to determine CCN sizes. The two DRI CCN spectrometers operated at different S ranges in order to accurately cover the entire CCN range from 1-0.01% S in three recent aircraft projects. Extensive agreement in an overlapping S range increased confidence in these measurements. The AIRS2 project was conducted in November-December 2003 over the Great Lakes region and eastern Canada with supercooled and mixed clouds. RICO project was conducted in December-January 2004-05 over the eastern Atlantic with warm convective clouds. The MASE project was conducted off the northern California coast in July 2005 with warm stratus clouds. Clean maritime air was encountered in RICO. Considerably modified maritime air was encountered in MASE. Wide variations in CCN and CN concentrations (3 orders of magnitude) were encountered in AIRS2. In both maritime environments--RICO and MASE-concentrations were higher above than below the clouds. Clouds seemed to have considerable effects on CCN spectra-mostly scavenging. Additional volatility and CCN size measurements were also made in all three projects. Volatility measurements were generally consistent with sulfate composition. CCN size measurements showed particles to be less soluble in dirtier air masses (those with higher particle concentrations).