In order to clarify whether that free radicals are actually the active oxygen species responsible for the observed decomposition, we used tert-butyl alcohol (TBA) as the radical scavenger (Buxton et al. 1988) and performed the experiments again by addingTBAto the testing solutions. As shown in Fig. 4, the presence of TBA results in an intensive inhibition of the degradation of both pesticides. Following a 6 min treatment, the remaining fraction of dichlorvos was 67.5 % in the presence of TBA. In comparison, only 4.9 % remained in absence of TBA. Similarly for dimethoate, the residue percentage was 88.0 % in the presence and 8.2 % in absence of TBA. The results indicate that TBA competes
with pesticide molecules to consume OHradicals, which are the primary species for contaminants decomposition by
DBD plasma (Zhang et al. 2008), consequently decelerate the decomposition rate of both pesticides. These data suggest that the degradation of organophosphate pesticides by DBD plasma is dominated by the free radicals.