Evaporating brine from frost flowers with electron microscopy and implications for atmospheric chemistry and sea-salt aerosol formation

0479453 - ÚPT 2018 RIV DE eng J - Journal Article
Yang, X. - Neděla, Vilém - Runštuk, Jiří - Ondrušková, G. - Krausko, J. - Vetráková, L'. - Heger, D.
Evaporating brine from frost flowers with electron microscopy and implications for atmospheric chemistry and sea-salt aerosol formation.
Atmospheric Chemistry and Physics. Roč. 17, č. 10 (2017), s. 6291-6303. ISSN 1680-7316. E-ISSN 1680-7324
R&D Projects: GA ČR(CZ) GA14-22777S
Institutional support: RVO:68081731
Keywords : experimental-computational approach * aqueous-solutions * boundary-layer * blowing snow * spectroscopic properties * low-temperatures
OECD category: Meteorology and atmospheric sciences
Impact factor: 5.509, year: 2017

An environmental scanning electron microscope (ESEM) was used for the first time to obtain well-resolved images, in both temporal and spatial dimensions, of lab-prepared frost flowers (FFs) under evaporation within the chamber temperature range from5 to18 degrees C and pressures above 500 Pa. Our scanning shows temperature-dependent NaCl speciation: the brine covering the ice was observed at all conditions, whereas the NaCl crystals were formed at temperatures below10 degrees C as the brine oversaturation was achieved. Finger-like ice structures covered by the brine, with a diameter of several micrometres and length of tens to 100 mu m, are exposed to the ambient air. The brine-covered fingers are highly flexible and cohesive. The exposure of the liquid brine on the micrometric fingers indicates a significant increase in the brine surface area compared to that of the flat ice surface at high temperatures, the NaCl crystals formed can become sites of heterogeneous reactivity at lower temperatures. There is no evidence that, without external forces, salty FFs could automatically fall apart to create a number of sub-particles at the scale of micrometres as the exposed brine fingers seem cohesive and hard to break in the middle. The fingers tend to combine together to form large spheres and then join back to the mother body, eventually forming a large chunk of salt after complete dehydration. The present microscopic observation rationalizes several previously unexplained observations, namely, that FFs are not a direct source of sea-salt aerosols and that saline ice crystals under evapora-tion could accelerate the heterogeneous reactions of bromine liberation.
Permanent Link: http://hdl.handle.net/11104/0275444