Direct Observation of Anthracene Clusters at Ice Surfaces

Abstract

Heterogeneous processes can control atmospheric composition. Snow and ice present important, but poorly understood, reaction media that can greatly alter the composition of air in the cryosphere in polar and temperate regions. Atmospheric scientists struggle to reconcile model predictions with field observations in snow-covered regions due to experimental challenges associated with monitoring reactions at air-ice interfaces, and debate regarding reaction kinetics and mechanisms has persisted for over a decade. In this work, we use wavelength-resolved fluorescence microscopy to determine the distribution and chemical speciation of the pollutant anthracene at the surfaces of environmentally relevant frozen surfaces. We show that anthracene adsorbs to frozen surfaces in monomeric form, but that following lateral diffusion, molecules ultimately reside within brine channels at saltwater ice surfaces, and in micron-sized clusters at freshwater ice surfaces; emission profiles indicate extensive self-association. We also measure anthracene photodegradation kinetics in aqueous solution and artificial snow prepared from frozen freshwater and saltwater solutions and use the micro-spectroscopic observations to explain the rate constants measured in different environments. These results resolve long-standing debates and will improve predictions of pollutant fate in the cryosphere. The techniques used can be applied to numerous surfaces within and beyond the atmospheric sciences.

pH-Buffering Capacity of Ice

“…Because the FCS has a considerable volume and thickness compared to the QLL, the effect from the ice surface is considered negligible. However, in the FCS, a variety of interesting phenomena occur that are not predictable from bulk solutions of the same composition and temperature. − In addition, freezing causes a significant change in the pH compared to its original value. − It is known that salt depositions and the incorporation of ions into the ice crystal lattice are responsible for the pH shifts in frozen salt solutions. , We here report different intriguing pH behavior found in frozen salt solutions. The measured pH is significantly different from that predicted from the freeze concentration effect alone, and, in many cases, the pH appears to approach ∼7 by freezing.…”

Role of an Ice Surface in the Photoreaction of Coumarins

“…Ice provides water/ice interfaces and chemical environments and can greatly accelerate the reaction rate . For example, some recent studies have shown that the oxidation rate of nitrite and the reduction rate of halate can be accelerated by ice due to the freeze concentration effect. − Ice can also increase the photodegradation rate of halobenzenes and the photodecarbonylation rate of dibenzyl ketones owing to the cage effect in ice. , Although it has been recognized that ice can improve the reactivity of chemicals, a clear picture of how ice surfaces relate to chemical transformations has remained elusive. ,− The chemical reactivity at ice surfaces differs greatly from that within complex ice matrixes. The reaction activity and selectivity are strongly determined by various physical and chemical properties of the ice surface, including the interfacial water-layering structure, two-dimensional confinement, and ice crystalline structure.…”

Water confinement in small polycyclic aromatic hydrocarbons

“…These results will provide insight into the confinement of water. The ideas of confinement we have developed in this work could enhance our understanding of anthracene cluster interactions with water ice 38 and in anthracene dimer exciplex formation in solution, 39 both of which have relevance in a wide variety of sub-disciplines.…”