T02_P25

New developments in the radiocarbon-based source apportionment for the water-soluble organic carbon fraction of airborne particulate matter

Strähl J¹,  Lechleitner F¹, Laemmel T¹, Geissbühler D¹, Salazar G¹, Szidat S¹

¹Department of Chemistry, Biochemistry and Pharmaceutical Sciences and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland

Air pollution is known for its adverse effects on human health (Burnett et al., 2014) and causes annually more than 6 million premature deaths (Gakidou et al., 2017). This demonstrates the exigency for effective mitigation strategies. Water-soluble organic carbon (WSOC) poses a large fraction of airborne particulate matter (Pöschl, 2005), and its source apportionment is crucial to understand the origin of pollution. The analysis of ¹⁴C is a powerful tool for source apportionment as it allows to discriminate between fossil and non-fossil emissions (Szidat, 2009). WSOC is extracted from samples using a wet oxidation procedure, with the advantage of low blank contamination and rapid sample processing times (Rauber et al., in prep.). The CO₂ generated from the wet oxidation can be analysed for its ¹⁴C content using an accelerator mass spectrometer equipped with a gas ion source (Ruff et al., 2007).

Here we present an optimized setup for the preparation and treatment of WSOC samples for ¹⁴C analysis that addresses concerns regarding sample recovery and blank contamination. A newly developed sintered needle minimizes losses of CO₂ during the sampling from the headspace of closed vials, while circumventing issues arising from the use of carbon-based glues. This allows the measurement of smaller sample amounts and simplifies the previous setup as no high-capacity water traps are needed anymore. A recently incorporated non-dispersive infrared CO₂ detector increases the accuracy of sample amount quantification. Finally, a detailed blank assessment on the new setup enables to detect possible remaining contamination sources and minimize their contribution.