Following the temporal and spatial variability of atmospheric 14CO2 across Switzerland to estimate source contributions to the national CO2 emissions.

Perturbations to the natural carbon cycle due to anthropogenic and induced natural emissions of carbon dioxide (CO₂) into the atmosphere are strongly linked with the current trend of global climate change. Efforts aiming at measuring amounts of CO₂ emitted by different ecosystems and industrial activities have been increasing in the past years, in order to gather information about necessary mitigations efforts towards reduced future emissions.

Radiocarbon (¹⁴C) measurements of atmospheric CO₂ are unique in their capabilities to provide information on carbon sources and transport. The radiocarbon method allows an apportionment between "modern" sources, with ¹⁴CO₂ signatures close to the global atmospheric average and fossil-fuel derived sources which are ¹⁴C-depleted. The capability to determine the fraction of fossil CO₂ in atmospheric samples provides insight on the contribution of different emissions to the current rise in atmospheric CO₂ concentration. When associated with meteorological data and atmospheric dispersion models, radiocarbon data can be used to identify fossil-fuel emissions patterns from a local to a regional scale, across time.

The Radiocarbon Inventories of Switzerland (RICH) project aims to build the first database and model of the distribution and cycling of ¹⁴C at a national scale and across the atmosphere, soils, rivers and lakes of the country. The project presented here (RICH-Air) will serve to construct complementary monitoring and snapshots approaches of atmospheric ¹⁴CO₂ measurement in this larger scope. For the monitoring aspect, air masses passing over Switzerland are collected and measured every two weeks at three tall tower sites situated over the populated Swiss plateau and one background site (Jungfraujoch). As for the snapshots, we focus on three industrial point sources (two cement plants, and a combined refinery-cement site) and use an Upwind-Downwind approach to have emissions and background samples at each site. As a complementary method, tree leaf samples will also be collected close to sites of interest, to have more temporally-integrated data.

First results show that the seasonality has a huge influence on the monitoring of the ¹⁴CO₂ signature, with a decrease in the winter months, due to limited atmospheric mixing, and accumulation of ground emissions. For the industrial hotspots, plume catching was shown to be challenging, even though an increased signal of a few ppm was generally visible.