Atmospheric peroxides over the North Pacific during IOC 2002 shipboard experiment

Atmospheric hydrogen peroxide and methyl hydroperoxide were determined onboard the Melville over the North Pacific from Osaka to Honolulu during May-June 2002. The concentrations of H₂O₂ and CH₃OOH increased from 0.64 ± 0.57 ppbv and 0.27 ± 0.59 ppbv in subpolar region (30-50°N) to 1.96 ± 0.95 ppbv and 1.56 ± 1.3 ppbv in subtropical region (24-30°N). The increase in concentrations towards the Equator was more pronounced for CH₃OOH than H₂O₂. In contrast, the levels of O₃ and CO were decreased at lower latitudes as air mass was more aged, denoted by the ratios of C₂H₂/CO and C₃H₈/C₂H₆. CH₃OOH concentrations showed a clear diurnal variation with a maximum around noon and minimum before sunrise. Frequently, the concentrations of peroxides remained over 1 ppbv in the dark and even gradually increased after sunset. In addition, the ratios of C₂H₄/C₂H₆ and C₃H₆/C₃H₈ were increased in aged subtropical air, which implies that these alkenes were emitted from the ocean surface. As a result, the reaction of these biogenic alkenes with O₃ was suggested to be a potential source for peroxides in aged marine air at lower latitudes.