CCN Spectra in ACE-1

Y. Xie, S.S. Yum, and J.G. Hudson (All at : Desert Research Institute, P.O. Box 60220, Reno, NV 89506-0220; 702-677-3119, Fax: 702-677-3157, e-mail;

Measurements of cloud condensation nuclei (CCN) concentrations and spectral shape are summarized for ACE-1. These were obtained with two nearly identical CCN spectrometers; one on the NCAR C- 130 aircraft and one at the Cape Grim monitoring station. Good agreement between these two instruments was achieved during a flyby of Cape Grim.

Vertical and temporal variations of CCN concentrations and spectra are displayed. These often showed very low concentrations in the vicinity of some clouds, which demonstrated cloud scavenging, which was sometimes the site of high CN (total particles most smaller than CCN) concentrations suggesting particle production. As with previous maritime measurements higher concentrations were often found above the boundary layer (Hudson and Frisbie 1991) suggesting that this is the source of particles for the boundary layer. Comparisons with CCN spectra obtained with the same instruments in the earlier Southern Ocean Cloud Experiment (SOCEX), which occurred in the same area at both a similar time of year and during the opposite season, revealed seasonal CCN variations. These may be due to differences in natural ocean emissions of DMS, variations in cloud scavenging, or variations in long range transport above the boundary layer. CCN spectra are also expressed in terms of the number of soluble ions to facilitate comparisons with aerosol chemistry measurements.

Measurements of CCN volatility and size vs. supersaturation (Hudson and Da 1996) from both ACE-1 and SOCEX are presented. These demonstrate that most of the time most of the CCN act like ammonium sulfate. Both of these sample processing mechanisms seem to manifest distinct differences depending on whether the particles had an anthropogenic origin. Differences in the volatility of CN for northern and southern Hemisphere measurements are noted.

Hudson, J.G. and X. Da, 1996: Volatility and size of cloud condensation nuclei. J. Geophys. Res., 101, 4435-4442.
Hudson, J.G. and P.R. Frisbie, 1991: Cloud condensation nuclei near marine stratus. J. of Geophys. Res., 96, D11, 20,795- 20,808.