Radiocarbon Inventories of Switzerland (RICH): Investigations into fossil CO2 emissions from cement factories and urban areas

The RICH (Radiocarbon Inventories of Switzerland) project aims to build the first database and model of the distribution and cycling of ¹⁴C at a national scale across the atmosphere, soils, rivers and lakes C pools. The subproject presented here (RICH-Air) will serve to construct complementary monitoring and snapshots approaches of atmospheric ¹⁴CO₂ measurement in this larger scope.

Radiocarbon measurements of atmospheric CO₂ provide unique information on its sources and subsequent transport. It allows the apportionment between biogenic and fossil sources, which are close to the contemporary atmospheric background and ¹⁴C-free, respectively. The determination of the fossil CO₂ fraction in air samples, can be used to identify fossil fuel emission patterns from a local to a regional scale. These efforts can then be used to plan and enforce future CO₂ emissions mitigation steps.

Presented here are preliminary results from investigations regarding the fossil factor in emissions of 3 Swiss cement factories and the urban area of Bern, Switzerland. The radiocarbon content of emissions were studied in multiple ways:

• Direct and downwind measurement of ¹⁴CO₂ emissions at cement factories
• Measurement of ¹⁴C content in tree leaves around cement factories and the urban area of Bern

The ¹⁴CO₂ results show that downwind emissions from cement factories are only accurate if the choice of local background is appropriate. Measured values, both direct and indirect, show that the fossil fraction of emissions is at least of 2/3, which is within the theoretical range for cement production. Also, different facilities seem to have contrasting mean fossil content in their emissions, probably due to their individual fuel mix. Finally, leaf samples show a gradient in ¹⁴C values, more depleted closer from the source, both for cement factories or the urban area, which is consistent with previous studies.