AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Assessing the Importance of Contact Ice Nucleation
DANIEL CZICZO, Yi-wen Huang, MIT
Abstract Number: 692 Working Group: Aerosols, Clouds, and Climate
Abstract The indirect effect of aerosols on global radiative forcing via its impact on cloud formation is one of the key unknown in aerosol science. Though our understanding of warm cloud formation is fair, our inability to fully describe cold cloud formation limits us in determining and predicting future climate change. It is believed that deposition freezing and immersion freezing are important ice nucleation mechanisms. Less known is the mode called “contact freezing”, which involves particles coming into contact with a water droplet to form an ice nuclei (IN). Some experimental studies have shown that ice formation due to contact freezing is initiated at higher temperatures than immersion freezing. However, few experiments have been performed using atmospherically relevant conditions.
We have constructed a laboratory experiment to assess the importance of ice nucleation via contact freezing. The system consists of an injector which is designed to bring a water droplet into contact with aerosol particles at controlled temperatures. The collision between the water droplet and the aerosol particle(s) may induce ice nucleation. A FTIR spectrometer is used to monitor ice presence and water vapor partitioning in the flow tube at multiple positions and help determine the onset temperature of contact freezing. At the end of the flow tube, a counterflow virtual impactor (CVI) is affixed to reject aerosol particles and let through only the large particles. The flow containing the IN is directed to the Particle Analysis by Laser Mass Spectrometry (PALMS) instrument which performs in situ chemical analysis of a single particle.