AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Contact Freezing Efficiency of Mineral Dust Particles Determined via Optical Tweezers
RYAN SULLIVAN, Hassan Beydoun, Kyle Gorkowski, Benjamin Dennis-Smithers, Toni Carruthers, Jonathan P. Reid, Carnegie Mellon University
Abstract Number: 535 Working Group: Aerosols, Clouds, and Climate
Abstract Contact freezing is believed to be the most efficient heterogeneous ice nucleation mechanism that catalyzes the freezing of supercooled cloud droplets. This process is notoriously difficult to study experimentally as it requires knowledge of how many particles have collided with the water droplet before it nucleates an ice crystal. Here we report the first use of optical tweezers to study contact freezing. A supercooled cloud droplet is tweezed in the temperature-controlled optical trap. The droplet is then bombarded with size-selected mineral dust particles. The tweezed droplet’s Raman spectrum that is retrieved in real-time provides a precise measure of the number of dust particles that have coagulated with the droplet. The occurrence of droplet freezing is also readily observed from the Raman spectrum and visual imaging. Together, this enables the precise determination of the freezing efficiency of various types of atmospherically-relevant mineral dust particles, by measuring the number of particle-droplet contact events required before ice nucleation occurs. The validity of the notion that contact freezing is the most efficient ice nucleation method has been explicitly interrogated for a variety of mineral dust samples. This new method helps to address fundamental deficiencies in our understanding of the ice nucleation properties of atmospheric particles.