The ozonolysis of ethene in dry synthetic air at atmospheric pressure and room temperature (298 2) K was investigated in a 6065-L reaction chamber by in situ analysis of stable species by FTIR and of total peroxy radicals PO2 PO2 HO2 + RO2) by a chemical amplifier instrument. The yields of radical production were determined based on steady state concentrations of the peroxy radicals and the partitioning between HO2 and RO2 derived from model simulations. The radical yield is 0.38 +/-0.02 for HO2 and 0.45 +/- 0.03 for PO2. (c) 2006 Elsevier B.V. All rights reserved.