First measurements of H2O2 and organic peroxide surface fluces by the Relaxed Eddy Accumulation technique

The relaxed eddy-accumulation (REA) technique was specially adapted to a high-performance liquid chromatographer (enzymatic method) and scrubbing coils to measure concentrations and fluxes of hydrogen peroxide (H2O2) and organic peroxides with a carbon chain C4, of which only methylhydroperoxide (MHP) and hydroxymethylhydroperoxide (HMHP) were detected. Flux measurements were carried out above the canopy of a Norway spruce forest in Germany (775 m a.s.l.) in NE Bavaria, Germany, during the BEWA2000 research cluster in summer 2001. This period was characterised by H2O2 maximum mixing ratios of 1 ppb and mixing ratios of organic peroxides below 200 ppt. Daily mean H2O2 deposition fluxes of ¿0.8±0.3 nmol m¿2 s¿1, MHP of ¿0.03±0.03 nmol m¿2 s¿1 and HMHP of ¿0.7±0.5 nmol m¿2 s¿1 were obtained. Profile measurements were performed as a qualitative comparison of the controlling mechanism of the surface exchanges. The REA as well as the profile measurements show that during daylight the surface exchanges of H2O2 and MHP over coniferous forest are mainly controlled by dry deposition. The high H2O2 dry-deposition velocity suggests a negligible surface uptake resistance for H2O2, whereas the significantly smaller MHP-deposition velocity indicates a significant surface uptake resistance. However, nighttime surface exchanges of these compounds should be further investigated since the in-canopy ozonolysis reaction is expected to affect exchanges. HMHP REA flux measurements show mainly deposition, whereas the ones based on the profile method suggest in-canopy chemical production