From EMSL: “How atmospheric ice forms”

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Environmental Molecular Sciences Laboratory (EMSL)

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New insights into atmospheric ice formation could improve climate models

ice

The formation of ice crystals in the atmosphere strongly affects cloud dynamics, cloud radiative properties and the water vapor budget, and thus plays an important role in climate. To gain new insights into this poorly understood process, researchers used state-of-the-art micro-spectroscopy and chemical imaging methods to characterize the physical and chemical properties of ice-nucleating particles sampled from ambient air.

The Impact

The study reveals the abundance of a given type of particle in the atmosphere can play a stronger role in ice formation than the particle-specific ice-nucleation propensity determined by the specific chemical and physical particle properties. These findings significantly advance our understanding of the underlying mechanisms that lead to ice formation in the atmosphere and could improve the accuracy of predictive cloud and climate models.

Summary

Researchers from Stony Brook University, EMSL, Lawrence Berkeley National Laboratory and University of the Pacific developed a novel methodology that enables comprehensive analyses of individual particles that act as ice nuclei, which trigger the formation of ice crystals in the atmosphere, as well as the entire population of particles found in ambient air. To characterize the particles’ physical and chemical properties, the researchers used micro-spectroscopy and chemical imaging methods, including computer controlled scanning electron microscopy with energy dispersive analysis of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). These methods provide information on the size, shape and elemental composition of a large number of individual particles.

By classifying the particles into categories based on physical and chemical properties, the researchers discovered ice-nucleating particles are not distinct from other particles. In other words, unique particle composition and shape were not sufficient to assess the potential to act as ice nuclei. Instead, the ice-nucleating particles are common in the atmosphere and do not always pose a “needle-in-the-haystack” challenge. This is in contrast to the traditional view that there are very few, but exceptional particles in the atmosphere with the right properties to become ice nuclei. Even particles that are not especially efficient at forming ice crystals can play an important role in this process when sufficiently abundant in the entire particle population, due to the large collective surface area for ice-nucleating reactions. The findings suggest cloud models should take into account the properties of the entire particle population in addition to those of individual ice-nucleating particles to accurately reflect the important role of particle abundance and total available surface area in ice formation.

Funding: Funding for sample collection was provided by the Atmospheric Radiation Measurement (ARM) Program sponsored by the DOE’s Office of Science’s Office of Biological and Environmental Research (OBER), Climate and Environmental Sciences Division (CESD). Funding for data analysis was provided by the U.S. DOE’s Atmospheric System Research (ASR) Program, OBER, CESD. Laboratory Directed Research and Development funds were provided by PNNL.

See the full article here.

EMSL is a national scientific user facility that is funded and sponsored by DOE’s Office of Biological & Environmental Research. As a user facility, our scientific capabilities – people, instruments and facilities – are available for use by the global research community. We support BER’s mission to provide innovative solutions to the nation’s environmental and energy production challenges in areas such as atmospheric aerosols, feedstocks, global carbon cycling, biogeochemistry, subsurface science and energy materials.

A deep understanding of molecular-level processes is critical to gaining a predictive, systems-level understanding of the impacts of aerosols and terrestrial systems on climate change; making clean, affordable, abundant energy; and cleaning up our legacy wastes. Visit our Science page to learn how EMSL leads in these areas, through our Science Themes.

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