Photochemistry of Solutes in Different Locations in/on Ice. Part II: Reaction Rate Measurements

Abstract:

Particularly in polar regions, photochemical reactions in snowpacks can be an important mechanism for transforming organic and inorganic compounds. Chemicals within snow and ice are found in three different compartments: distributed in the bulk ice, concentrated in liquid-like regions (LLRs) within the ice matrix (such as at grain boundaries), or in quasi-liquid layers at the air-ice interface. While some experiments suggest reaction rates may vary in these different compartments, it is not clear if the reaction rates are different or if the changes are due to variations in the reaction environment (such as photon flux). A companion presentation discusses our work identifying solute location in laboratory ice samples; here, we describe experimental measurements of reaction rates in different ice compartments.

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants in snow and ice. We first prepared aqueous solutions of a single PAH. We then froze these samples using various methods that segregate the solute into different locations in the ice matrix. With simulated sunlight, we illuminated these samples and measured photon flux (using 2-nitrobenzaldehyde) and the photodecay of the PAH. We will discuss differences in PAH photochemistry as a function of location in the ice sample and the implications of these results for environmental snow and ice.