AGS-PRF: Photochemistry of Impurities in Nature-Identical Snow Crystals

Hullar Ted, Oakland CA

Investigators

Abstract

This Postdoctoral Research Fellowship proposal focuses on characterizing photochemical reactions (caused by sunlight) on laboratory-generated snow crystals. The research will evaluate the impact of crystal type on photochemical reaction rates, and compare these findings to observations from previous work conducted in frozen solution and other natural snow analogs. Because many of the important reactions in snow are photochemically driven, the exact nature of the reaction environment must be well characterized in order to fully understand chemical reactions in snow. The proposed project has the following objectives: (1) develop and build a machine to make nature-identical snow and incorporate impurities into the synthetic snow; (2) determine the location of impurities in this nature-identical snow; (3) determine the relative actinic fluxes for various impurity locations and with various crystal habits; (4) for synthetic snow made in liquid nitrogen, a commonly used snow analog, determine the location of impurities and local actinic flux; and (5) compare photochemistry of polycyclic aromatic hydrocarbons (PAHs) in various compartments of nature-identical and liquid nitrogen synthetic snows. Identifying the locations of co-condensed impurities in nature-identical snow crystals will improve understanding of the possible suite of chemical transformations in the crystals and the eventual fate of their reaction products. Measurements of the sensitivity of photochemical parameters to crystal habit will provide information important for proper modeling of snow and ice photochemistry. By determining photolysis rates for several PAHs under varying snow crystal morphologies and impurity locations, this research will provide useful information about reaction rate constants under natural conditions, including sensitivity to impurity location or crystal habit. These data will help to resolve current discrepancies in measured photolysis rates. The proposed research will significantly advance the understanding of snow and ice photochemistry by providing both a refined tool to study the natural environment and substantial data to more accurately understand photochemical reactions in snow and ice.