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Interfacial Chemistry of Ice: Photolysis and Acid-Base Equilibria in the QLL and Brine

Applicant Bartels-Rausch Thorsten
Number 178962
Funding scheme Project funding (Div. I-III)
Research institution Paul Scherrer Institut
Institution of higher education Paul Scherrer Institute - PSI
Main discipline Physical Chemistry
Start/End 01.08.2018 - 31.07.2022
Approved amount 571'060.00
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All Disciplines (3)

Discipline
Physical Chemistry
Condensed Matter Physics
Climatology. Atmospherical Chemistry, Aeronomy

Keywords (11)

cryosphere; snow chemistry; premelting; acid-base; trace gases; aerosol; Hydrogen bonding; adsorption; photochemistry; Polar research; quasi-liquid layer

Lay Summary (German)

Lead
Die Struktur in der die Wassermoleküle an Eisoberflächen angeordnet sind wurde seit Faradays Zeiten untersucht und zeigt interessante Abweichungen von der Struktur im Inneren der Eiskristalle. Dieser Unterschied beruht auf dem Aufbrechen der Kristallstruktur und liegt in einer erhöhten Flexibilität. Dies wirkt sich auch auf chemische Reaktionen an der Eisoberfläche aus. Bisher ist noch wenig über die Zusammenhänge zwischen der Struktur an der Eisoberfläche und chemischen Reaktionen bekannt und ein kein konzeptionelles Verständnis fehlt.
Lay summary
Dieses Projekt zielt darauf ab chemische Reaktionen an der Eisoberfläche zu untersuchen und den Zusammenhang zwischen der Anordnung der Wassermoleküle an der Eisoberfläche und dem chemischen Verhalten herzustellen. Wir planen dazu (i) das Säure-Base Gleichgewicht und (ii) Photolysereaktionen an der Eisoberfläche zu untersuchen. (i) Säure-Base Gleichgewichte sind ein zentrales Konzept der Chemie. Neuere Studien deuten an, dass die Dissoziationseigenschaften an der Eis- und auch Wasseroberfläche von denen in wässrigen Lösungen abweichen. Ein genaueres Verständnis der Säure-Base Eigenschaften ist auch wichtig um Photolysereaktionen an der Eisoberfläche besser zu verstehen, da die lichtgetriebene Reaktivität vom Säure-Base Gleichgewicht abhängt. Wir werden (ii) die Photolyse von Spurenstoffen an der Eisoberfläche untersuchen auch um weitere Rückschlüsse auf die Struktur an der Oberfläche und auf die Dissoziationseigenschaften der Reaktionspartner schliessen zu können. 

Unser Projekt wird ein detailliertes Bild der physikalisch-chemischen Grundlagen von Prozessen an der Eisoberfläche entwickeln. Motiviert wird das Projekt mit der Bedeutung dieser Reaktionen in der Atmosphärenchemie und dem Interesse an diesen grundliegenden Fragestellungen der allgemeinen physikalischen Chemie. 
Direct link to Lay Summary Last update: 29.06.2018

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
155999 The impact of the physical micro-environment of impurities in snow on their re-distribution during metamorphism, chemical reactivity, and transfer to ice core archives. 01.05.2015 Project funding (Div. I-III)
149629 Surface Sensitive Investigations of the Interaction of Atmospheric Acidic Trace Gases with Ice Surfaces 01.03.2014 Project funding (Div. I-III)
121857 The uptake of peroxynitric acid on ice surfaces: The role of grain boundaries and of dissociation 01.06.2009 Project funding (Div. I-III)
169176 Multiphase kinetics and chemistry at aqueous solution and mineral oxide - air interfaces 01.01.2017 Project funding (Div. I-III)

Abstract

The capability of acids to form hydrogen bonds has been found essential to their dissociation (Devlin et al., 2002; Gutberlet et al., 2009). The dissociation of acids plays is a principal process in heterogeneous chemistry of the atmosphere (George et al., 2015; Zhou and Zhu, 2016). In particular, the dissociation and photochemistry of nitric acid/ and nitrous acid at frozen and liquid air - water interfaces has since long attracted scientific interest (Finlayson-Pitts, 2003; Huthwelker et al., 2006), most notably due to the pivotal role that this surface chemistry plays in modifying the nitrogen oxide budget and thus the oxidative capacity of the atmosphere (Grannas et al., 2007; Zhou et al., 2011). Despite general agreement that aqueous interfaces feature distinct chemical properties compared to the bulk, interfacial acid-base chemistry is only ill defined (Mishra et al., 2012; Kong et al., 2017). In particular, the strong acids HNO3 and also HCl have been observed to be stabilized in their molecular form at the surface of concentrated aqueous solutions (Baldelli et al., 1998; Morris et al., 2000; Clifford et al., 2007; Brastad and Nathanson, 2011) and on ice surfaces (Wren and Donaldson, 2012; Kong et al., 2017). This unique behaviour at surfaces of solutions and of ice is thought to be related to missing capability to form hydrogen bonds at these surfaces. That said, we come back to surfaces in the troposphere as host for heterogeneous photochemistry of nitric acid. The presence of molecular HNO3 with a limited number of hydrogen bonds is deemed essential to explain the high photolysis rates overserved at surfaces in general (Zhou and Zhu, 2016) and at the surface of amorphous ice < 120 K (Marcotte et al., 2015).Given the importance of multiphase chemistry of snow for Earth’s geochemical cycles (Grannas et al., 2007; Grannas et al., 2013; Bartels-Rausch et al., 2014), this project aims at developing a fundamental understanding of interfacial chemistry in the temperature range of -40°C to 0°C. The quasi-liquid layer (QLL) emerging in this temperature range introduces motional energy and thus flexibility to the hydrogen bonding network at the ice surface (Bartels-Rausch et al., 2014). A molecular level understanding of the resulting changes to the interfacial chemistry is essentially missing. An immediate outcome of our preceding SNF project is the emerging picture of the QLL where solutes form liquid-like solvation shells within a generally ice-like interfacial region. We propose therefore to investigate the product yields of HNO3 photochemistry in the interfacial region, as these are very sensitive to the chemical environment (Benedict et al., 2017). We hypothesise that the chemistry is distinct from the liquid phase. Further, we propose to investigate the interfacial dissociation of HNO3 and HONO to developing predictive capabilities. We propose that the coexistence of molecularly physisorbed acid at the surface and solvated anions within the QLL, questioning the application of simple acid base concepts across interfaces (Kong et al., 2017), responds to temperature, concentration and type of acid. More general, we will address the importance of surface chemistry relative to bulk chemistry, both within the “quasi-liquid” interface and in liquid brine to elaborate on differences between the interface and a phase with respect to photochemistry and acid-base equilibria. The unique approach of the proposed research is to combine two surface sensitive spectroscopic methods to directly probe the hydrogen-bonding network at the interface and the concentration and dissociation degree of the dopant and of reaction products with detailed kinetic studies (Kong et al., 2017). Quantitative depth profile of the acid within the interfacial region guarantee the distinction between adsorbates at the surface and solutes deeper in the interfacial region. The data on the adsorption, dissociation, and photochemistry are essential to cryospheric and atmospheric science. The concept of interfacial chemistry and the role of hydrogen bonds is also of interest to the general chemistry community, given that hydrogen bonding and proton transfer are central concepts in chemistry.
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