Chemical Morphology Controls Reactivity of OH Radicals at the Air–Ice Interface

Abstract

At the air−ice interface, some aromatic compounds such as benzene and anthracene are surprisingly unreactive toward OH. This may be a consequence of the poor solvation of these compounds at the interface, resulting in clustering there. We test this hypothesis by comparing the reaction of OH with pyrene, a 4ring polyaromatic hydrocarbon (PAH), to reactions of OH with the more water-soluble compounds coumarin and 7-hydroxycoumarin (7OHC). We observe that OH reacts readily with coumarin and 7OHC at both liquid and frozen air−water interfaces. Pyrene, a much less soluble compound, reacts with OH at the liquid surface but not at the air−ice interface. We report evidence of pyrene aggregation at the ice surface based on its broadened and redshifted emission spectrum alongside fluorescence mapping of anthracene, a closely related 3-ring PAH, which shows bunching at the ice surface. By contrast, fluorescence mapping shows that coumarin is fairly homogeneously distributed at the air−ice interface. Together, these results suggest that the limited reactivity of some compounds toward OH at the ice surface may be a consequence of their propensity to self-aggregate, demonstrating that chemical morphology can play an important role in reactions at the ice surface.

Uptake of Hydrogen Peroxide from the Gas Phase to Grain Boundaries: A Source in Snow and Ice

“…The preference of H 2 O 2 for grain boundaries in environmental snow and ice might result in significant variations in the local concentration of H 2 O 2 . This is relevant as such non-uniform chemical morphologies and highly concentrated patches of reactants at grain boundaries and elsewhere in the ice have recently been shown to impact chemical reactivity in frozen systems strongly. ,, Grain boundaries in natural snowpacks occur at the contact face of individual snow grains . As grain size, shape, and arrangement change with time in snowpacks (metamorphism), detailed studies observing the impact of grain boundaries at different stages of metamorphism are timely to elucidate the mechanism and the environmental impact more extensively.…”

Spontaneous Production of I2 at the Surface of Aqueous Iodide Solutions

“…Fluorescence experiments were carried out using a setup based on those we have used in the past, − and described fully in McLay et al The unfocused output of a wavelength-tunable pulsed Nd:YAG laser-pumped optical parametric oscillator (OPO) system operating at a pulse frequency of 20 Hz was directed toward either a circular sample dish, 6 cm in diameter and about 1 cm deep, or a 1 cm path-length cuvette. Typical pulse energies at the laser head were between ∼0.5 and ∼1.2 mJ per 3 ns pulse.…”

“…A complete spectrum was not measured, either in the bulk or at the surface. Previous work 31,33,35 has shown that the bulk aqueous and aqueous surface fluorescence spectra are essentially identical for clean water surfaces. The luminol fluorescence intensity at 420 nm was monitored following excitation at 350 nm in the bulk and at the water surface as a function of the concentration of added salt.…”

“…Therefore, one can potentially also track the changes in luminol fluorescence intensity to monitor its reactive or quenching interactions with other species. − Here we use glancing angle laser-induced fluorescence spectroscopy (GALIF) to provide experimental evidence for spontaneous I 2 formation at the surface of aqueous iodide solutions through tracking the loss of fluorescence intensity as a probe. GALIF experiments have been used extensively by us in the past decades to study chemistry at the air–water interface. − …”

Experimental determination of the partitioning of representative organic pollutants to the air–water interface

“…15 The GALIF technique used in these experiments was developed and has been used over the past two decades to investigate surface partitioning, pH and reaction kinetics at a variety of environmentally relevant surfaces. [15][16][17][18][19][20] For example, Mmereki et al 16 measured the surface uptake coefficients of anthracene and pyrene from the gas phase to freshwater surfaces and to octanol-and hexanoic acid-coated surfaces. A 2-3 times enhancement in the surface uptake coefficient was seen when octanol was present at the surface, as compared to when the surface was freshwater.…”