Environmental photodegradation processes are important in the breakdown of pollutants, as well as in the global element cycles. This thesis will describe several physical organic chemistry projects aimed at increasing our understanding of photodegradation processes as they pertain to specific environmental concerns and potential future technological applications. Following this introductory chapter, a reaction-diffusion theory of singlet oxygen is developed. This theory was developed to improve our understanding of photochemical reactions in systems that contain microenvironments. By thinking of these systems on the nanoscale, we are able to explain the enhanced photochemical reactivity of hydrophobic probe molecules and accurately estimate the physicochemical characteristics of the respective local microenvironment. Chapter 3 applies the reaction-diffusion theory towards explaining the observed enhanced inactivation of waterborne pathogens within wastewater stabilization ponds. The next chapter describes the synthesis of nanoscale photoreactors, a step towards a possible technological application, and a test of the reaction-diffusion theory. The final chapter focuses on another photochemically produced reactive intermediate, hydroxyl radical, and describes the development of fluorescent hydroxyl radical probes.