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Chlorine in Water and Air: The Effects of Sodium Chloride on Pollutant Photodegradation in Seawater and Sea Ice, and Indoor Hypochlorous Acid Levels Following Surface Cleaning with Bleach

Date

2024-05-14

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Type

Thesis

Degree Level

Doctoral

Abstract

This thesis covers two separate projects: first, we investigate the effects of chloride (Cl–) on anthracene photodegradation kinetics in seawater, saline aqueous solutions, and in frozen saltwater solutions. Next, we measure hypochlorous acid (HOCl) concentrations during bathroom surface cleaning with a bleach-based product to inform human exposure risks during and following cleaning activities. The environment is complex, having multiple phases that have different physical and chemical properties. Pollutants deposited throughout the environment can react differently based on these varying properties. Changes in reactivity have been observed for polycyclic aromatic hydrocarbons (PAHs) when assessing their photodegradation kinetics in aqueous, organic, and frozen settings. Polycyclic aromatic hydrocarbons are ubiquitous, toxic environmental pollutants with adverse health effects, whose degradation products are often just as or more toxic than the parent PAH. To better understand the environmental fate of PAHs, an understanding of their reactivity in these compartments is necessary but is also complicated by technical challenges associated with measuring reaction kinetics in complex condensed phases relevant to the environment. We measured the PAH anthracene’s photodegradation kinetics in seawater and in sea ice proxies compared to liquid and frozen freshwater samples. The presence of chloride salt enhanced photodegradation kinetics in both aqueous and frozen media by factors of ~ 1.5 and ~ 4, respectively, compared to anthracene’s photodegradation kinetics in pristine water. This research helps us better understand and predict anthracene’s and potentially other aromatic pollutants’ environmental fate, particularly in non-pristine environments. Cleaning indoors can release pollutants that affect indoor air quality. Bleach, a common cleaning agent, releases active chlorine as hypochlorous acid (HOCl) which can affect air quality and health. Hypochlorous acid emissions that evolve during cleaning have been measured as room averages but emissions near the point of application have not been assessed. We measured time-resolved HOCl emissions in a residential bathroom during application of a bleach product using cavity ring-down spectroscopy and varied the inlet location with respect to the disinfected surface. Hypochlorous acid emissions increased rapidly following bleach application and remained elevated for up to 40 minutes until the surface was scrubbed and rinsed. Emissions closest to the point of application exceeded 10 ppmv, while those measured further away were 20 times less than near-source emissions on average. The greatly elevated near-source HOCl emissions suggest that people close to the source may experience higher exposure to HOCl than what is expected based on existing reports for room-averaged emissions.

Description

Keywords

aromatic compounds, photodegradation kinetics, photooxidation, air-ice interface, ice surface, ice chemistry, seawater, cryosphere, environmental fate, hypochlorous acid, indoor air quality, surface cleaning, bleach

Citation

Degree

Doctor of Philosophy (Ph.D.)

Department

Chemistry

Program

Chemistry

Advisor

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