Emissions from natural ecosystems, broadly classified as biogenic volatile organic compounds (BVOCs), contribute 90\% to the VOC budget. Individual BVOCs vary widely in their reaction rates with atmospheric oxidants, making their atmospheric impact highly dependent on VOC composition. Their emissions are also dependent on vegetative make up and a number of meteorological and ecological variables. However, the ecological and physical drivers of their emissions is becoming more variable in a changing climate, leading to greater uncertainties in models. Increasing the monitoring of individual compounds can improve our understanding of the drivers of these emissions and the impact of individual chemical species on atmospheric composition. Improved understanding of BVOC composition can better emission models and, SOA and ozone formation predictions. To study the atmospheric impacts and physical drivers of BVOCs, a GC-FID was adapted for automated hourly sampling and analysis. The details of the hardware and software used for the system are described in detail to enable future long-term BVOC measurements in additional locations. The instrument was deployed at a measurement tower in a forest in central Virginia for year-round collection of BVOC concentrations. Using two years of collected hourly data, this work assesses the chemical impacts of individual BVOCs on time scales ranging from hour to year. This work identifies the importance of both concentration and chemical structure in determining atmospheric impacts. Additionally, seasonality in the concentration of some biogenic species has large implications for atmospheric reactivity in the warmest months of the year, particularly ozone reactivity. Using ecological and meteorological data collected at the site in conjunction with the BVOC data, the drivers of BVOC concentrations and their seasonality are identified. Comparison between this data and current models, reveal important deviations which may lead to large modeled uncertainties. Furthermore, the collected data has been made publicly available to aid in future research regarding BVOCs. / Doctor of Philosophy / The earth hosts a number of sources of atmospheric emissions. These range from human-driven sources such as vehicles and factories, to natural sources such as trees and grass. The content of these emissions, amongst others, become a part of a large reactor (the atmosphere), that interact with each other. The interaction of these emissions with atmospheric oxidants forms a gas (ozone) with implications for human and ecosystem health, and secondary organic aerosol (the leading component to smog). However, the extent to which these emissions react with atmospheric oxidants is largely dependent on the structure of individual compounds. A major focus of this dissertation is to show that compounds with reactive structures can have a large impact on atmospheric composition, and that the quantity of emissions can be as important as compound structure.
Understanding the impact of individual compounds in the atmosphere requires improved measurement techniques, capable of detecting the compounds of interest over long time periods. Therefore, another focus of this work was the adaptation and deployment of an instrument capable of detecting some of the most reactive species in the atmosphere, volatile organic compounds emitted from forests. The instrument deployed in this work was a gas chromatography flame ionization detector (GC-FID), which detects compounds largely composed of carbon and hydrogen. The instrument was adapted to run automatically through the development of an electronics box and software program interfaced with the GC-FID. Following development, the instrument was deployed to a remote forest research site for two years. The data collected from this work was used to determine the impact of individual compounds on atmospheric composition. Findings from this work could be used to improve a range of atmospheric models. Small changes in emissions (human or plant) contribute to the total VOC budget which can have large implications for the formation of ozone and SOA. Therefore, increased understanding of the BVOC concentrations and emission driver will aid in predicting these atmospheric components.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/110409 |
| Date | 02 June 2022 |
| Creators | McGlynn, Deborah Fairbanks |
| Contributors | Civil and Environmental Engineering, Isaacman-VanWertz, Gabriel, Pusede, Sally E., Marr, Linsey C., Little, John C. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International, http://creativecommons.org/licenses/by-nc-sa/4.0/ |
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