Date of Award

December 2017

Degree Name

Master of Science (MS)

Department

Chemistry

Advisor(s)

Tara Kahan

Keywords

Aerosols, Aqueous-Organic, Atmosphere, PAH, Photolysis, Sodium Chloride

Subject Categories

Physical Sciences and Mathematics

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are dangerous pollutants. The photolysis kinetics of PAHs are of interest because they are carcinogenic and can increase in toxicity through photodegradation into secondary products. They are often associated with particulate matter. The composition and physical properties of the particulate matter can affect PAH photolysis kinetics. We investigated the effects of sodium chloride on the photolysis kinetics of the PAH anthracene in water and octanol as well as mixed-phase solutions (water-octanol), which were used as models for aqueous-organic aerosols. A non-linear dependence on sodium chloride concentrations was observed. Sodium chloride enhanced photolysis at concentrations up to 0.25 M due to increased singlet oxygen (1O2) production, and suppressed photolysis at higher concentrations because of anthracene quenching. A positive dependence on sodium chloride concentration above sodium chloride’s saturation limit in aqueous solution (6.1 M) suggested that new reaction pathways, potentially on the surface of solid sodium chloride, may be occurring. 0.25 M sodium chloride increased rate constants in octanol and aqueous-organic mixtures, but to a lesser extent than in water. An increase of a factor of 9 was observed when 0.25 M sodium chloride was included in aqueous solutions, while the increase in octanol was a factor of 2. Stirring aqueous-organic mixtures during photolysis increased photolysis rates in the absence of salt, but had inconsistent effects in the presence of 0.25 M sodium chloride.

Access

Open Access

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