HR: 1340h
AN: A53B-1146    [Abstracts]
TI: Singlet Molecular Oxygen on Ice: Rates of Formation and Steady State Concentrations
AU: * Bower, J P
EM: jpbower@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
AU: Anastasio, C
EM: canastasio@ucdavis.edu
AF: Department of Land, Air, and Water Resources, University of California, Davis, One Shields Avenue, Davis, CA 95616, United States
AB: Singlet molecular oxygen (¹O₂^*), the first electronically excited state of molecular oxygen, reacts rapidly with certain types of environmental pollutants such as furans, phenols, and polycyclic aromatic hydrocarbons (PAHs). Its formation requires the absorption of light by a chromophore (a.k.a. sensitizer), which subsequently transfers energy to ground state molecular oxygen. In the environment, ¹O₂^* chemistry has been studied primarily in the aqueous phase, such as in surface waters or cloud and fog drops. In this work, we expand our current understanding by investigating the rate of formation (R_f) and steady state concentration ([¹O₂^*]) of ¹O₂^* on ice.
To investigate ¹O₂^* kinetics, we use a chemical probe technique in which photoformed ¹O₂^* reacts with furfuryl alcohol (FFA). To generate ¹O₂^*, we illuminated frozen samples containing a sensitizer (Rose Bengal, RB) at 549 nm. The concentration of total solutes in each sample was controlled using sodium sulfate (Na₂SO₄). Following illumination, the decay of FFA was measured using high performance liquid chromatography (HPLC). Ice tests were conducted at 253, 263, and 268 K. Liquid tests for comparison were conducted at 278 K. Results showed dramatically faster (~10⁴) FFA decay on ice than in liquid samples prepared from the same solutions, in agreement with the calculated solute concentration factor in the quasi-liquid layer (QLL) on ice compared to bulk solution. Varying the concentration of RB resulted in similar changes in both R_f and [¹O₂^*], with magnitudes of change close to those expected. Changing temperature and total solutes, both of which control the volume of the QLL on ice, revealed two model regimes: FFA as a major (1) or minor (2) sink of ¹O₂^*. Experimental results from the former regime show good agreement with expected values for both R_f and [¹O₂^*]. Experiments in the later regime are currently in progress. We will also discuss the potential implications of ¹O₂^* to the chemistry of naturally occurring snow and ice.
DE: 0317 Chemical kinetic and photochemical properties
DE: 0322 Constituent sources and sinks
DE: 1827 Glaciology (0736, 0776, 1863)
DE: 1863 Snow and ice (0736, 0738, 0776, 1827)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting