Fig. 6

Total Fe at 7d versus hydroxyl radical (HO^•) generation at 60 min for the INGV samples for the 2001 and 2002 eruptions and for ‘standard’ samples, first presented in Horwell et al. (2007), which have since been reanalysed on several occasions (ETNA4/11/02: HO^• ×6, Fe ×4; MON5/6/99 HO^• ×7, Fe ×5; CER30/11/95 HO^•. ×4, Fe ×5; PIN4/7/91 HO^• ×3, Fe ×3; most reanalyses involved between 1 and 3 runs of HO^• and 1 run of Fe). Error bars are standard deviations from the averages of these reanalyses (for MON and PIN, the horizontal bars are smaller than the symbol), and the averages of 3 runs for HO^• for the samples analysed for this paper