H2O2 and organic peroxide measurements in an orographic cloud: The FEBUKO experiment

The H2O2 and organic peroxides are known to be important oxidants in cloud-water, influencing the oxidising capacity of the atmosphere. Measurements of H2O2 in cloud-water have shown a wide range of concentrations depending on the season and measuring site. Moreover, organic peroxide measurements are scarce in spite of their importance. Measurements of peroxides were carried out in the Thuringian Forest, Germany, during the FEBUKO research cluster in the Fall 2001. The measuring stations were located at three sites: upwind (gas phase), summit (cloud-water and gas phase) and downwind (gas phase). Analysis was achieved by high performance liquid chromatography (enzymatic method). From the different peroxides only H2O2 was detected in the gas phase at the upwind site with mixing ratios <130 ppt. In the cloud-water, besides hydrogen peroxide (H2O2), hydroxymethylhydroperoxide (HMHP), 1-hydroxyethylhydroperoxide (1-HEHP) and methylhydroperoxide (MHP) were also detected with concentrations normalised with the liquid water content up to 1.30, 0.075, 0.065 and 0.015 nmol m−3, respectively. Organic peroxides (HMHP+1-HEHP+MHP) constitute up to 80% of the total peroxides during nighttime while during daytime they accounted for about 14%. Consequently, organic peroxides might play an important role in nighttime cloud chemistry.