Chromatographic Separation and Wet Oxidation of Oxalic Acid from Aerosols for Radiocarbon Source Apportionment

Rauber, Martin; Uglietti, Chiara; Salazar Quintero, Gary Abdiel; Szidat, Sönke (April 2019). Chromatographic Separation and Wet Oxidation of Oxalic Acid from Aerosols for Radiocarbon Source Apportionment. In: 12th International Conference on Carbonaceous Particles in the Atmosphere. Vienna (Austria). 03.-06.04.2019.

Radiocarbon analysis is a powerful technique for the apportionment of fossil and non-fossil sources of carbonaceous aerosols. This technique can be applied to total carbon, organic carbon and elemental carbon, as well as more specific fractions of aerosols. We aim at compound-specific radiocarbon analyses (CSRA) of dicarboxylic acids (DCAs) using a one-step chromatographic separation followed by a chemical wet oxidation and subsequent radiocarbon measurement with an accelerator mass spectrometer (AMS).
DCAs have received much attention because of their role as cloud condensation nuclei and are found in urban, rural, and marine sites. This raises questions about their sources, precursors, and formation processes. Gaseous precursors can react in the atmosphere forming secondary organic aerosols (SOA). Both primary organic aerosols (POA) and SOA can undergo aging processes, from which low-molecular-weight DCAs are produced. The dominant DCAs in aerosols are by a large margin oxalic acid, followed by malonic and succinic acid. Previously, the sources of formic, acetic, and oxalic acid in aerosols were investigated using stable carbon isotopes (Fisseha et al., 2009). In contrast, owing to their low prevalence, radiocarbon measurements of DCAs are seldom conducted. Fahrni et al. (2010) performed CSRA of DCAs using a two-step chromatographic separation. There, water-soluble organic compounds were separated by ion chromatography (IC), followed by high-performance liquid chromatography (HPLC). The fractions were collected, water removed on a vacuum line, and the compounds oxidised to CO2at 950°C with cupric oxide in a quartz glass tube for AMS measurement.
In this work, chemical wet oxidation (Lang et al., 2016) was used to oxidise oxalic acid directly after IC separation without a second chromatographic separation and an additional concentration step. Wet oxidation directly forms CO2from carbonaceous compounds in the eluate whereas inorganic compounds such as sulphates remain unaffected. This simplifies the procedure while achieving lower blanks by omitting additional concentration and separation steps. We focus on the apportionment of fossil and non-fossil sourcesof oxalic acid extracted from filters sampled at urban and rural sites. As a consequence of their low content, pooled fractions of malonic and succinic acid will be measured additionally.
Fahrni et al., Radiocarbon 52, 752-760 (2010)
Fisseha et al., Atmos. Environ. 43, 431-437 (2009)
Lang et al., Radiocarbon 58, 1-11 (2016)

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