Atmospheric particulate matter contains significant amounts of oxalic acid. However, the origins of this dicarboxylic acid have been discussed controversially and mechanisms for a plant-derived formation (biogenic emissions and wood burning, left picture) as well as fossil sources (use of fossil fuels, right picture) have been taken into account.
Here, isolation of oxalic acid from aerosols and subsequent radiocarbon (¹⁴C) measurements hold the key to source apportionment. The underlying principle is the difference in the radiocarbon content in plants and fossil fuels: While the biosphere is in equilibrium with the cosmogenic radiocarbon in the atmosphere, fossil fuels are extinct in radiocarbon as they have been cut off from the atmospheric ¹⁴C for many half-lives. First results indicate a high plant-derived contribution of 80% for two sites in Switzerland.

This work was carried out in the group of PD Dr. Sönke Szidat.

References:

• S. M. Fahrni, M. Ruff, L. Wacker, N. Perron, H. W. Gäggeler and S. Szidat;
  "A preparative 2D-chromatography method for compound-specific radiocarbon analysis of dicarboxylic acids in aerosols"
  Radiocarbon, 52, 752-760, (2010); Abstract.