Dissertation

Segmented Flow Coil Equilibrator for Continuous Measurement of Volatile Organic Compounds in Seawater of the Polar Oceans

Wohl, Charel

2021

Overview

Volatile organic compounds (VOCs) are a group of molecules that influence aspects of atmospheric chemistry such as oxidation chemistry and particle formation. Most VOCs are produced from a variety of anthropogenic and natural sources; with emissions from the oceans least well known/ quantified. In this thesis I focus on methanol, acetone, acetaldehyde, DMS and isoprene. Uncertainty persists as to the factors influencing their variability in seawater concentrations. The polar oceans are particularly undersampled regions with few to no measurements of these compounds, which is partially due to a lack of suitable instrumentation. To increase available instrumentation, this thesis describes the development of a Segmented Flow Coil Equilibrator coupled to a commercially available Proton Transfer Reaction-Mass Spectrometer for measurements of VOCs in seawater. Its main advantage lies in its ability to measure underway and discrete samples. The method is used to make depth profile and underway measurements in the Canadian Arctic Archipelago during sea ice melt season. Highest VOC concentrations are generally observed at the surface, apart from DMS and isoprene which sometimes display a subsurface maximum. Generally, highest surface concentrations of VOCs are observed in partial ice cover. Concentrations of acetone and acetaldehyde were about 30 - 50 % higher in partial ice cover compared to ice-free waters. This thesis also presents ambient air, underway and depth profile measurements from a transect in the subpolar Southern Ocean, used to calculate surface saturations and air - sea fluxes. Correlations with other biogeochemical data allowed me to elucidate factors controlling seawater concentrations of these VOCs. This dataset contains the first evidence of a statistically significant, but small diel change (on the order of 8 - 26 %) in seawater isoprene, acetone and acetaldehyde concentrations in the open ocean. The measurements presented in this thesis will be useful to constrain ocean source/sink strength. The analysis points towards factors controlling the global variability of these compounds in the ocean.

• Publisher: ProQuest Dissertations & Theses