Rauber, Martin (2022). Radiocarbon Source Apportionment of Carbonaceous Aerosols using Water-Soluble Organic Carbon and Oxalate Fractions. (Thesis). Universität Bern, Bern
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22rauber_m.pdf - Thesis Available under License Creative Commons: Attribution (CC-BY 4.0). Download (7MB) | Preview |
Abstract
Atmospheric aerosols are known for their effects on human health and the climate. Understanding the sources and formation processes of atmospheric aerosols is crucial for targeted pollution mitigation. In this work, radiocarbon (14C, half-life = 5730 ± 40) was utilised for source apportionment of fossil-fuel and biogenic fractions. In the first project, low-loaded aerosol filters from the Norwegian archipelago Svalbard were analysed with an optimised organic carbon (OC)/elemental carbon (EC) separation method and direct water-soluble OC (WSOC) measurement. The filter material subjected to OC/EC separation was water extracted for charring reduction, i.e., a reduction of OC pyrolysis. A novel thermal-desorption model for the correction of 14C-EC after thermal-optical separation was introduced. This thermal-desorption approach should supersede the current linear extrapolation approach for EC correction. The eluate containing WSOC from the water extraction was used for direct WSOC measurement by chemical wet oxidation. Although not feasible with the Svalbard filters, radiocarbon measurements of the water-insoluble OC (WINSOC) fraction are also possible with higher loaded filters. Additional to EC and WSOC, total carbon (TC) was measured with residual filter material not utilised for water extraction. In the second project, oxalic acid was used for compound-specific radiocarbon analysis (CSRA). Oxalic acid the most prevalent dicarboxylic acid (DCA) contained in atmospheric aerosols. Due to their ability to act as cloud condensation nuclei, DCAs became of great interest. However, their sources and formation process are not fully understood, and previous studies indicate that DCAs may be formed as secondary organic aerosols. Here, extracted aerosol filters were separated by a single ion chromatography step followed by a chemical wet oxidation for radiocarbon measurement. Although CSRA is much more elaborate than WSOC analysis, our approach is simpler than previous attempts of CSRA for oxalate while providing low processing blanks. Results from multiple sites indicate a predominant biogenic formation of oxalate as a secondary organic aerosol. In the third project, aerosol filters from the Norwegian Troll station in Antarctica were analysed. Despite the very low loadings, radiocarbon analysis of the TC, WSOC and WINSOC fractions were successfully performed. Our analysis indicate that 14C-depleted primary marine aerosol (PMA) sources dominate in all measured carbonaceous fractions in austral summer. Secondary marine aerosols and biomass burning are only minor sources. PMA originates in the Southern Ocean surrounding Antarctica. Upwellings in the Southern Ocean bring aged dissolved organic carbon (DOC) to the surface while sea spray from breaking waves brings the 14C-depleted DOC as PMA into the atmosphere.
| Item Type: | Thesis |
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| Dissertation Type: | Cumulative |
| Date of Defense: | 17 August 2022 |
| Subjects: | 500 Science > 540 Chemistry |
| Institute / Center: | 08 Faculty of Science > Department of Chemistry, Biochemistry and Pharmaceutical Sciences (DCBP) |
| Depositing User: | Sarah Stalder |
| Date Deposited: | 02 Dec 2024 11:40 |
| Last Modified: | 02 Dec 2024 23:25 |
| URI: | https://boristheses.unibe.ch/id/eprint/4052 |
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