Seminar

Abstract

Atmospheric ice nucleating particles play an important role in initiating the ice-phase in clouds at temperatures warmer than -38 deg C. Several competing mechanistic models that hold different views about the underlying process of ice nucleation have been proposed in the literature. The relative importance of different sources of ice nucleating particles, including mineral dust and carbonaceous aerosols, are poorly understood. Ice nucleation measurements remain challenging because number concentrations are low and multiple modes of ice nucleation must be characterized. An emerging and unsolved question is the sensitivity of cloud processes, precipitation, and climate to the atmospheric ice nuclei pool.

In this presentation I will delve into data obtained from recent laboratory experiments and field studies of immersion mode ice nucleation. First, I will show how experiments can be performed to identify nucleation rates for individual active sites and how the distribution of nucleation sites can be used to model the time-dependence of ice nucleation for a population of particles. Second, I will report results from atmospheric measurements of ice nucleating particles, including a survey derived from cloud water and precipitation samples, and ambient measurements performed in North Carolina, Colorado, and California (ACAPEX/Calwater 2 campaign). Discussion will include (1) methodological constraints involved in ice nucleation sampling, (2) a synthesis of atmospheric ice nucleating particle concentration between -5 and -38 deg C, and (3) recurring links between the emission of biologically-derived particles and ice nucleating particle concentration.

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Markus Petters is an associate professor at North Carolina State University investigating atmospheric aerosols and their influence on physical and chemical processes in the atmosphere.