ABSTRAcT

Snow is a very good scavenger of atmospheric pollutants, which can be deposited on the ground and
accumulated in the seasonal snowpack. In the polar regions, solar irradiation of the organic or
inorganic constituents of snow can have an impact upon the composition of the lower atmosphere and
in the snowpack. Chemicals and photoproducts can enter the atmosphere or be released via melt water
into the environment during the periods of temporal warming. Our knowledge concerning the
photodegradation processes of chemicals in matrices of ice and snow is still very limited.
Laboratory experiments are important for better understanding the behavior of organic compounds in
pristine arctic environments.

Organophosphorus pesticides are widely used throughout the world, which mitigates the use of more
toxic organochlorine pesticides. Fenitrothion and methyl-parathion (with very similar structures)
are among the organophosphates that can absorb directly ultraviolet (UV) light and undergo
transformations in liquid solutions and in ice. In this thesis, the main photoproducts in ice and
water found were oxons, nitrophenols and denitration product in the case of fenitrothion. Oxons can
also photodegrade in the environment or can be responsible for causing toxicological effects, such
as the inhibition of acetylcholine esterase. Comparison of the photodegradation of both compounds
(fenitrothion and methyl-parathion) in water and in ice can then be used to predict their
subsequent fate in the environment.

Artificial snow is a reaction matrix, in which many photochemical studies can be conducted. In this
thesis, contaminated snow samples prepared by different methods were investigated. Aqueous
solutions were sprayed into liquid nitrogen (-196 °C) or inside a walk-in-chamber at (-35 °C). The
specific surface area of artificial snow was measured to make up ~ 400 cm^2 g^-^1 based on the
photodegradation of valerophenone and surface coverage by hydrophobic compound. The diffusion and
restrictions of benzyl radicals were explored based on the bimolecular reaction known as the
Norrish type I process of 4-methyldibenzyl ketone. The temperature dependent cage effect
(probability of radical recombination) of such a reaction in artificial snow was investigated.
Limited mobility of radicals was found to occur at higher temperatures than previously measured in
frozen solutions. Density functional theory calculations supported the observation that molecules
are self-associated, which is in contrast to frozen solutions.