Understanding the role of ice nucleating particles for heterogeneous ice formation in atmospheric clouds
EMSL Project ID
51057
Abstract
Atmospheric ice nucleation affects cloud radiative properties, lifetime and precipitation behavior with far-reaching implications for global climate. While homogeneous freezing of water droplets only occurs at temperatures below 235 K, heterogeneous freezing, facilitated by organic, inorganic, or biological ice nuclei (IN) can occur at much warmer temperatures, within a few degrees of 273 K. Although the presence and atmospheric concentration of IN is well known to affect glaciation in mixed-phase clouds, mechanisms of heterogeneous ice nucleation remain poorly understood and it remains challenging to predict physical or chemical properties of clouds under a wide range of atmospherically relevant conditions. In order to develop an improved mechanistic understanding of heterogeneous ice formation, it is essential to observe molecular behavior near the water-particle interface at atmospherically relevant temperatures. We need to develop an integrative approach based upon measurements of ice nucleation of various particles, characterization of the chemical and morphological structure of IN, tools that measure the ordering and mobility of water at the solid-liquid interface and nanometer-scale mapping of of the nucleation sites and water near those nucleation sites on atmospheric IN. Our research will (1) identify particular nucleation-active sites on known IN, (2) characterize and map the chemical identity and morphology on the surface of each particle, and (3) measure the local environment, interactions and dynamics of water within nanometers of the surface of the particle. We will initially focus on two types of previously-identified efficient IN; k-feldspar and pseudomonas syringae. We will use a multimodal and interdisciplinary approach that combines observations of immersion mode IN activity using drop freeze assay, measurement of the nanoscale chemical identity and morphology based upon infrared scattering scanning near-field optical microscopy (IR s-SNOM) and scanning electron microscopy (SEM) measurements, measurements of the interfacial structure of water using vibrational sum frequency generation and attenuated total internal reflection infrared spectroscopies. Finally, we will explore a novel approach towards nanoscale imaging of the water structure on the surface of IN based upon in liquid IR s-SNOM recently developed by EMSL. We will use this instrument to investigate the chemical identity of the IN as well as the degree of ordering in the water. Successful implementation for our application will enable us to image both chemical identity of IN with ice nucleation properties with <20 nm spatial resolution. Our new integrative approach including measurement of ice nucleating properties of aerosols and provide qualitatively new and mechanistic insight into heterogeneous ice formation. The methods we develop will be readily generalizable and portable to investigation of the other heterogeneous solid-liquid interfaces relevant to catalysis, electrochemical systems, and geochemical interactions.
Project Details
Project type
Exploratory Research
Start Date
2019-11-26
End Date
2021-06-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)