Diagnostic tests for quantitative measurements of singlet molecular oxygen on ice

Singlet molecular oxygen (1O2*) can rapidly react with atmospheric pollutants such as furans, phenols, polycyclic aromatic hydrocarbons (PAHs), and reduced sulfur species. Furthermore, 1O2* might be an important oxidant of atmospheric trace species on frozen atmospheric particles and drops. Thus, a quantitative understanding of 1O2* activity on ice is essential in assessing its importance to the chemistry of the troposphere of cold regions. In aqueous samples, the loss of furfuryl alcohol (FFA) can be measured to determine 1O2* concentrations. Using this method, samples are illuminated and the photoformed 1O2* reacts with FFA, decreasing its concentration over time. This process, however, is confounded by the fact that the decay of FFA can occur via other pathways, such as direct photolysis or reaction with other oxidants, including OH.

The goal of this work is to investigate the behavior of 1O2* on ice so that its concentrations can be determined using the decay of FFA. To achieve this, we are working through a series of diagnostic tests, taking into account complications presented by direct photolysis, reactions with other oxidants, and changes in quasi-liquid layer volume and composition. To examine effects of specific oxidants, sources of 1O2* and OH (rose bengal and HOOH, respectively) are added to simulated snow solutions with and without methionine, an efficient 1O2* quencher and OH scavenger. With these laboratory liquid and ice samples we hope to understand the photochemical behavior of 1O2* on ice and use methionine, or other scavengers, to discriminate between decay due to 1O2* and other loss mechanisms for FFA. We will discuss results from these tests, as well as preliminary measurements of 1O2* concentrations on snow from Greenland.

Hexagonal-plate ice crystal pictured above used by permission from SnowCrystals.com