Aircraft Characterization of Individual Ice Nuclei and Cloud Condensation Nuclei using Single Particle Mass Spectrometer, SPLAT II

ALLA ZELENYUK (1), Dan Imre (2), Peter Liu (3), Anne Marie Macdonald (3), Richard Leaitch (3)

(1) Pacific Northwest National Laboratory, (2) Imre Consulting, (3) Environment Canada, Ontario, Canada

     Abstract Number: 734
     Last modified: May 14, 2010

Abstract
The relationship between the properties of aerosol particles and the formation and properties of clouds, i.e. aerosol indirect effect, is among the most uncertain aspects in our current understanding of climate change. The efficacy with which aerosol particle activates to form cloud droplet or ice crystal depends on the size and composition of individual aerosol particles.
During the month of April 2008 our single particle mass spectrometer, SPLAT II, was deployed on board the National Research Council of Canada Convair-580 aircraft in part of the Indirect and Semi-Direct Aerosol Campaign (ISDAC). The main scientific objective of ISDAC was to improve our understanding of how changes in the size, composition, and concentration of aerosols influence cloud properties and the associated radiative forcing.
SPLAT II characterized several millions particles and obtained information on their size, composition, number concentrations, size distributions, density, and asphericity with high temporal resolution. When sampling in clear air SPLAT II measured a wide range of particle compositions, including sulfates mixed with organics, nitrates mixed with organic, processed and freshly emitted sea-salt, dust particles, and a significant number of biomass burning particles. Many of these particle types appeared in aerosol layers that had horizontal and vertical filamentous structures.
Since the main focus of this campaign was to characterize cloud-aerosol interaction, large fraction of the data was collected through the CVI inlet, which was modified to yield artifact-free information on the ice nuclei (IN) and cloud condensation nuclei (CCN) properties.
Despite the very low ice crystal concentrations that were typically observed in ISDAC, we measured properties of thousands of ice-nuclei. Analysis of the data on IN revealed that the large fraction of IN particles is either metallic or composed of dust; and that a significant fraction of these particles are as small as 100 nm in diameter.