An excess of Cl-36 in modern atmospheric precipitation

Measurements of Cl-36 were performed in modern annual precipitation from ma ny world-wide distributed stations. The measured deposition fluxes were on the average half an order of magnitude larger than fluxes calculated from t he cosmic-ray-induced atmospheric production. These discrepancies were tent atively explained by recycling of bomb Cl-36 from the biosphere as methyl c hloride (CH3Cl) into the troposphere, destruction of CH3Cl by OH reactions and subsequent tropospheric deposition of Cl-36. Simulations were performed for natural atmospheric production, bomb fall-out and recycling of Cl-36. The simulations including recycling were qualitatively able to explain the excess in deposition fluxes, especially for tropical regions. (C) 2000 Else vier Science B.V. All rights reserved.