Atmospheric peroxy radicals:: ROXMAS, a new mass-spectrometric methodology for speciated measurements of HO2 and ΣRO2 and first results

ROXMAS (ROx Chemical Conversion/CIMS), a novel method for atmospheric speciated measurements of HO2 and the sum of organic peroxy radicals (SigmaRO(2)) developed by MPI-K, has been successfully deployed in a field campaign on Monte Cimone, Italy, June-July 2000. The method relies on amplifying chemical conversion of peroxy radicals to gaseous sulfuric acid via the chain reaction with NO and SO2 and detection of the sulfuric acid by CIMS. Speciated measurements have been realized by diluting atmospheric air in either N-2 or O-2 buffer, thus exploiting the dependence of the conversion efficiency of RO2 to HO2 on [O-2], [NO], and [SO2]. Speciated measurements of HO2 and RO2 are required to provide further insight into radical partitioning and thus to elucidate further the mechanisms of the oxidation of volatile organic compounds in the troposphere. This methodology yields useful speciated results for atmospheric conditions where CH3O2 makes a major contribution to total RO2. Under other conditions it gives an upper limit for [O-2] and a lower limit for [SigmaRO(2)]. (Int J Mass Spectrom 213 (2002) 91-99) (C) 2002 Elsevier Science B.V.