Aqueous photochemistry in the urban environment: investigating reactive oxygen species generated by road dust, urban grime and photoactive minerals.

Abstract

In urban environments, certain chemical compounds are able to absorb sunlight and generate reactive species, which can react with pollutants and affect their environmental fate and lifetime. In this thesis, I explore the photochemical production of reactive species by three microenvironments relevant to urban areas: road dust, urban grime and photoactive minerals. In the first part of my thesis, I studied road dust, which is a large source of primary particulate matter in urban areas. I found that eight different road dust samples produce singlet oxygen upon illumination, with the insoluble fraction responsible for the majority of the singlet oxygen production. This chapter gives insight into the components of road dust that produce singlet oxygen and highlights its photochemical activity in the environment. In the second part of my thesis, I investigated road dust samples studied in Chapter 2, along with urban grime. I showed that illuminated road dust and urban grime samples produce hydroxyl radicals, which expands our knowledge of the oxidants generated by road dust and serves as a starting point in investigating the oxidant profile generated by urban grime. In the final section of my thesis, I examined the validity of using synthetic proxies for the photoactive component of mineral dust. I found that the photodegradation of methylene blue by natural titanium containing minerals was two orders of magnitude lower than its photodegradation by commercially synthesized titanium dioxide, meaning that synthetic titanium dioxide is not a good proxy to use when studying the aqueous photochemistry of mineral dust. Overall, this research expands our understanding of the reactive species that are photochemically generated by different microenvironments in urban areas. With this knowledge, we will better comprehend how pollutants transform in these environments, thereby leading to a better understanding of how they influence the surrounding air and water quality.