College of Science Theses and Dissertations
Permanent URI for this collectionhttps://hdl.handle.net/1969.6/1175
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Browsing College of Science Theses and Dissertations by Author "Abdulla, H."
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Item Determining ethanol concentration in wet deposition in the eastern United States and South Texas(2019-12) Sharma, Bipin; Felix, J. D.; Abdulla, H.; Conkle, J.This study represents the first comprehensive analysis of wet deposition ethanol in the Eastern US and South Texas to better comprehend how ethanol emissions are affecting atmospheric ethanol concentrations. Ethanol concentrations measured in 204 wet deposition samples collected at five Atmospheric Integrated Research Monitoring Network (AIRMoN) sites in the Eastern US between February 2018 to January 2019 ranged from below the detection limit of 19 nM to 4160 nM and concentrations measured in 48 rain events in South Texas during the same time period ranged from below the detection limit to 13195 nM. The volume weighted average ethanol concentration of AIRMoN samples ranged from 208 nM to 1017 nM while the volume weighted average ethanol concentration in South Texas was 1177 nM. Adding the five AIRMoN data to the previous empirical-based global wet deposition flux estimated by using data from 12 sites globally, the global wet deposition ethanol flux was estimated to be 2.7 ± 1.3 Tg/yr. No significant correlation + - 2- - 2+ + 2+ + was observed between ethanol and any analytes (NH4 , Cl, SO4 , NO3 , Ca , Na , Mg , K , PO43- and H+) in almost all sites in the study, likely due to the difference in atmospheric residence time and emission sources. When investigating AIRMoN data as a whole, a significant correlation was observed between ethanol and chloride and ethanol and sodium ion concentration, suggesting common inputs from forest or marine sources. Significant seasonal variations of ethanol were not observed for any sites, which suggest a continuous emission of ethanol to the atmosphere. Anthropogenic and biogenic (with and without C4 plants) contributions to atmospheric ethanol were estimated using ISOERROR and SIAR isotope mixing models. Excluding C4 plants in the models, our results suggest that the greater fraction of ethanol in South Texas (ISOERROR: 70.6 ± 12.8%; SIAR: 68.4 ± 12.7%) and NY67 (ISOERROR: 66.1 ± 11.9%; SIAR: 63.4 ± 12.9%) was emitted from anthropogenic sources; the contribution of biogenic (ISOERROR: 49.6%; SIAR: 52.2 ± 12.7%) and anthropogenic (ISOERROR: 50.4%; SIAR: 47.8 ± 12.7%) sources was equivalent in WV99 while the biogenic (ISOERROR: 63.2 ± 8.3%; SIAR: 60.4 ± 16.5%) sources contribution was dominant in TN00. Including C4 plants in the models, our results suggest that the greater fraction of ethanol in South Texas (ISOERROR: 58.1 ± 14.8%; SIAR: 56.9 ± 16.0%) and NY67 (ISOERROR: 63.4 ± 12.6%; SIAR: 58.3 ± 19.5%) was emitted from anthropogenic sources; the contribution of biogenic sources was dominant in TN00 (ISOERROR 74.2 ± 10.1%; SIAR: 67.2 ± 18.3%) and WV99 (ISOERROR 70.7%; SIAR: 67.8 ± 14.8%). Therefore, as the distribution of C3 and C4 plants varies from site to site, this study suggests that it is important to consider the types of plants around each site before assigning the representative endmember value for biogenic sources. Results of this study are important as it provides atmospheric scientists, environmental chemists and policy makers with a baseline of atmospheric ethanol concentration in order to help determine the efficacy of future ethanol fuel use and to help quantify the wet deposition ethanol sink. As ethanol fuel consumption and thereby emissions are increasing globally, it is important to understand the magnitude of all ethanol sources and sinks and their impacts in the atmosphere.Item Investigating the isotopic composition of reactive nitrogen in a South Texas estuary (Baffin Bay)(2018-08) Campbell, Jacquelyn; Felix, J. D.; Wetz, M.; Abdulla, H.Harmful algal blooms (HABs) have the potential to adversely affect the water quality of estuaries and, consequently, their ability to support healthy and diverse ecosystems. Since 1989, Baffin Bay, a semi-arid south Texas estuary, has experienced harmful algal blooms. This work investigates the stable isotopic composition of reactive nitrogen (Nr) (δ15N-DON, δ15N-NH4+, and δ15N-NO3-) in samples collected monthly at nine stations over the period of one year, and provides insight into Nr sources and processing in Baffin Bay. The following seasonal stages summarize the influences affecting δ15N values throughout the study: 1) Elevated δ15N-DIN values (4.9‰ ± 5‰) in the winter indicate the influence of a source of DIN with a relatively high δ15N such as wastewater or septic effluent, which may also contribute to elevated DON concentrations (46.4 µM ± 10 µM) and δ15N-DON values (9.5‰ ± 2‰). 2) The increase of NH4+ concentrations in the spring from run off concurrent with steady δ15N-DIN values (3.6‰ ± 6 ‰) implies phytoplankton assimilation of DON as evidenced by high δ15N-DON values (12‰ ± 6‰) and low DON concentrations (36µM ± 13.2 µM). 3) Evidence of photo-ammonification is observed throughout the summer due to elevated δ15N-DON values (10.5‰ ± 3‰) and low DON concentrations concurrent with low δ15N-DIN (-1‰ ± 5‰) and elevated NH4+ concentrations. 4) The accumulation of DON concentrations in the fall are consistent with phytoplankton detritus, which is supported by the decrease in δ15N-DON value averages in the fall and winter (9.8‰ ± 2 ‰). Remineralization during this stage is supported by low δ15N-DIN values (-2.3‰ ± 4.4‰). Additionally, salinity gradients and cross plots of δ15N values and concentrations support the idea that while both mixing and processing can influence δ15N values and patterns observed throughout the year, Nr processing (i.e. photo-ammonification, phytoplankton uptake, bacterial mineralization) may be the dominant mechanism for N cycling in Baffin Bay. Overall, this study increases constraints on the Nr isotope budget in Baffin Bay and offers insight into the role of DON in the N-cycle in a south Texas estuary.Item Molecular characterization of dissolved organic matter in Sao Paulo, Brazil wet deposition by ultra-high resolution mass spectrometry(2022-05) Seymore, Jackson; Felix, J. D.; Abdulla, H.; Conkle, J.Rainwater dissolved organic matter (DOM) is a complex mixture of organic compounds, the composition of which remains to a large extent unknown. This is despite its central role in a host of fundamentally important atmospheric processes (e.g. aerosol hygroscopicity, light absorption, etc.). The molecular composition of DOM has been used to infer emission sources and investigate atmospheric reactions that produce secondary organic aerosols (SOA), which comprise the main contributor of uncharacterized compounds in rainwater organics. This work illustrates the molecular composition of DOM in rainwater collected from February 2020 to June 2021 (n = 32 of rain samples) in Ribeirão Preto, SP (21.166 S, 47.845 W) using complimentary methods of traditional ion chromatography cooperatively with Orbitrap mass spectrometry and novel statistical analysis. This approach provides a detailed, ultra-high resolution, high throughput method for future rainwater DOM investigations which is demonstrated here with direct-injection, positive mode electrospray ionization. Using this method, 41,383 total molecular formulas in 32 samples were identified over the mass range m/z+ range of 80 to 800; among them 2,788 molecular formulas were unique. DOM character in São Paulo rainwater is revealed to be largely influenced by organic nitrogen, as 2,397 of the unique formulas identified contained nitrogen. This represents 86.0% of the total variety of organic compounds identified, with many of these likely peptides or amino acid derivatives. These findings also show that in terms of variety and number the general proportions of elemental formula classes remain relatively consistent over many samples, but the composition of the individual classes varies as function of its constituent emission sources. Recent pandemic related influences on anthropogenic activity as well as biomass burning in the São Paulo region of Brazil are seen through variations in rainwater DOM characteristics. Rainwater collected prior to the COVID-19 pandemic’s emergence in Brazil is distinct from reduced anthropogenic activity rainwater in both DOM character—seen in the increase in primary compounds and direct amino acid contribution, wider range of O:C ratios, and the absence of atmospheric NOx related CHON oligomers—and major ion content—marked by a reduction in sulfate, nitrate, potassium, and formate. Clustering analysis shows that these distinctions are mostly driven by changes in anthropogenic reactive nitrogen emissions as well as in part to seasonal influence. This research highlights the potential for public policy to reduce the emission of air pollutants and other biologically relevant anthropogenic emissions, particularly through reducing traffic loading and expanding remote working.