Date Thesis Awarded

5-2022

Access Type

Honors Thesis -- Open Access

Degree Name

Bachelors of Science (BS)

Department

Chemistry

Advisor

Rachel O'Brien

Committee Members

Beverly Sher

Marc Sher

Abstract

Water films on outdoor surfaces, such as dew, can act as a reservoir for organic molecules deposited from the atmosphere and they present a potential reactive medium for chemical transformations. To better understand the flux of volatile organic compounds from evaporating films, the composition and reactivity of the complex mixture of dissolved organic material (DOM) found in these films need to be characterized. Previous studies have measured the salts and the small organic molecules in dew collected on clean Teflon surfaces or condensers. Here, we expand on this by probing the organic chemicals found on natural outdoor surfaces covered in dew water. Over the course of three years, samples of dew and frost were taken from leaf (bush and grass) surfaces in Sussex and around the Williamsburg area in Virginia. For a detailed look at the complex chemical composition of the lower volatility fraction, six samples were analyzed by Fourier transform ion cyclotron mass spectrometry (FT-ICR-MS), which found over 9900 different molecular formulas across all samples. These molecular formulas contain a range of compounds which include C, O, H, N, P, and S. Smaller and higher volatility compounds were characterized using derivatization and extraction of the dew water samples combined with gas chromatography coupled with mass spectrometry (GC/MS). Preliminary data shows the presence of small carbonyls including acetone, benzaldehyde, and acetaldehyde, but spectra were too complex to characterize most compounds. The dew water samples were also found to have a range of colors from transparent colorless to dark brownish-yellow and photolysis coupled with UV/Vis showed varying reaction rates for light-absorbing chemicals in the mixtures. Fluorescence spectroscopy showed that all samples tested have fluorophores. The pH values of dew water samples ranged from 4.3 to 6.5, with an average of 5.4. Based on all data, samples from grass likely contain DOM, carbohydrates, and humic- and protein-like compounds from many different sources. Teflon collected samples are different and may contain protein-like compounds. The research presented here demonstrates the chemical complexity of this system with sources dependent on location, weather, and day of collection. In addition, it shows work developing an efficient method and suggestions for future work for characterization that can be used for dew water comparison by location and time.

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