Nonchromophoric organic matter suppresses polycyclic aromatic hydrocarbon photolysis in ice and at ice surfaces

We have investigated the effects of organic matter (OM) that does not absorb sunlight ("nonchromophoric") on the reactive environment presented by bulk ice and ice surfaces. Fluorescence spectroscopy showed that the presence of as little as 2.5 × 10^-4 M octanol or decanol reduces the extent to which naphthalene self-associates at ice surfaces, which indicates that naphthalene partitions between ice and organic phases present there. We also measured photolysis kinetics of the polycyclic aromatic hydrocarbons (PAHs) anthracene, pyrene, and phenanthrene in bulk ice and at ice surfaces containing 2.5 × 10^-5 M to 7.5 × 10^-3 M OM. In bulk ice, even the lowest concentrations of OM reduced photolysis kinetics to below our detection limits. Organic matter also reduced measured photolysis kinetics of PAHs at ice surfaces, but generally to a lesser extent than in bulk ice. Our results support previous reports that bulk ice and ice surfaces present distinct reaction environments, and show for the first time that OM can affect PAH photolysis kinetics by altering the physical environment within bulk ice and at ice surfaces.