Date

2018

Department or Program

Chemistry

Additional Department or Program (if any)

Physics

Primary Wellesley Thesis Advisor

Rachel H.R. Stanley

Additional Advisor(s)

Chris Arumainayagam

Additional Advisor

James Battat

Abstract

Isotopes of the five stable noble gases (He, Ne, Ar, Kr, and Xe) are useful in analyzing physical processes in the environment such as air-sea gas exchange and sea ice formation and melting. Traditional measurements of noble gases are costly and time-consuming because of the need to transport water samples to analyze in a laboratory-based mass spectrometer. Field deployable mass spectrometers were developed as a low-cost method to increase the temporal resolution of the measurements. Our system utilizes a quadrupole mass spectrometer in tandem with a gas equilibrator cartridge to continuously measure equilibrated gases from water with ambient air as a calibration standard. The reproducibility of the system is better than 0.7% for all gas ratios in a lab environment. However, our current configuration is not optimized for measuring helium because of the high permeability of helium through many of the materials used. Nonetheless, measuring helium will yield insight into quantifying bubble processes, which significantly affects rates of air-sea gas exchange. Our mass spectrometer configuration was thus extended to measure helium by switching from fused silica capillaries to stainless steel capillaries and switching from Tygon tubing to Viton tubing. The equilibration and precision of the new system was compared to that of the old configuration. Leak tests were performed on the old and new configuration to assess whether the leakiness of the system has improved. Results showed effective measurements of He with precisions better than 0.80% for both He/Ar and He/Kr at water temperatures of 22°C and above. Further optimization is needed to improve the equilibration of He and Ne at water temperatures of 10°C.

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