10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Liquid-Liquid Phase Separation in Organic Aerosol Particles Investigated by Environmental X-Ray Microscopy
Jan-David Förster, Christopher Pöhlker, Haijie Tong, Markus Ammann, Florian Ditas, Jörg Raabe, Ulrich Pöschl, David Walter, Benjamin Watts, MEINRAT O. ANDREAE, Max Planck Institute for Chemistry
Abstract Number: 1377 Working Group: Aerosol Chemistry
Abstract Atmospheric aerosol particles play important roles in the atmosphere and climate system by scattering and absorbing solar radiation and affecting cloud properties. The atmospheric life cycle and climate impacts of aerosol particles largely depend on their phase and mixing state and, particularly, on their hygroscopic response under variable relative humidity. A systematic understanding of the aerosol’s dynamic evolution under variable atmospheric conditions is crucial to estimate their overall impact on the atmosphere. Advanced micro-spectroscopy, especially scanning transmission x-ray microscopy with near-edge x-ray absorption fine structure spectroscopy (STXM-NEXAFS), is a suitable technique to address these dynamic processes with high spatial and chemical resolution.
Humidity variations in the atmosphere can change the morphology and mixing state of aerosol particles substantially [1]. In order to mimic atmospheric aerosol processing and particularly humidity cycling, we built an environmental cell for STXM-NEXAFS, which allows to control temperature, humidity, and pressure in the cell precisely and reliably. STXM-NEXAFS further allows to conduct a chemical characterization of the separated phases.
Here we present results on the observation of liquid-liquid phase separation in laboratory generated secondary organic aerosol particles along the lines of recent studies [2]. Our results show a miscibility gap of the SOA/water system above ~95 % for certain SOA types down to submicron particle sizes. STXM-NEXAFS further allows to conduct a chemical characterization of the separated phases.
Acknowledgements. This work has been funded by the Max Planck Society. We acknowledge the Paul Scherrer Institute, Villigen, Switzerland for providing synchrotron radiation beamtime at the PolLux beamline of the SLS.
[1] C. Pöhlker et al., Geophys. Res. Lett., 41, 3681-3689 (2014). [2] M. Song et al., Atmos. Chem. Phys., 17, 11261-11271, 2017.