Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 3 4 2003 10.5194/acp-3-999-2003 http://www.atmos-chem-phys.net/3/999/2003/ http://www.atmos-chem-phys.net/3/999/2003/acp-3-999-2003.html http://www.atmos-chem-phys.net/3/999/2003/acp-3-999-2003.pdf 999 1005 2003-07-14 The detection of solar proton produced ¹⁴CO P. Jöckel C. A. M. Brenninkmeijer M. G. Lawrence P. Siegmund Department of Air Chemistry, Max-Planck-Institute for Chemistry, Mainz, Germany Atmospheric Composition Division, Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands Major solar eruptions (coronal mass ejections) are accompanied by massive ejections of protons. When these charged particles head for the Earth through the interplanetary magnetic field with high flux and energy, a solar proton event (SPE) is recorded. Strong SPEs, in which energetic protons penetrate the atmosphere in large numbers are rare, but do have chemical effects (Crutzen, 1975; Jackman et al., 1990, 2001).  They also have nucleonic effects by which they can almost instantaneously increase the atmospheric production of radio-nuclides, including ¹⁴C (radiocarbon), but this has never been demonstrated. We show, using satellite observations and modeling, that the 2nd most intensive set of SPEs on record, that of August-December 1989, must have caused detectable increases in atmospheric ¹⁴CO. This is confirmed by a sequence of peaks in the Baring Head (NZ) time series of ¹⁴CO observations (Brenninkmeijer, 1993), probably providing a unique indication of production of ¹⁴C by solar protons, thus demonstrating the use of SPE ¹⁴CO as an atmospheric tracer.