Extended Abstract (124K)6.4
First Measurements of H2O2 and Organic Peroxides Surface Fluxes by the Relaxed Eddy Accumulation Technique
Jessica M. Valverde-Canossa, Max-Planck-Institute for Chemistry, Mainz, Germany; and G. Moortgat and G. Schuster
Hydrogen peroxide (H2O2) is an important chemical constituent of the troposphere. Its production occurs mainly in the gas phase by recombination of two HO2 radicals. The primary sink for H2O2 is the uptake into existing aerosols acting as an oxidant, which is mainly responsible for the conversion of SO2 into sulphuric acid (H2SO4). Near the surface dry deposition also represents a major sink for H2O2 due to its high solubility and reactivity. Recent reports indicate another possible source of H2O2: the ozonolysis of both anthropogenic and biogenic alkenes. A study of the ozonolysis of isoprene has shown that H2O2 is produced by the reaction of the Criegee intermediate with water vapour in the absence of light. Measured H2O2 yields from a series of anthropogenic and biogenic hydrocarbons have already been used to predict the relevance of the ozonolysis reactions for tropospheric chemistry.
The first measurements of H2O2 surface fluxes applying the Relaxed Eddy Accumulation Technique (REA) were successfully carried out above the canopy of a spruce forest in Germany. The REA technique was specially adapted for the measurements of H2O2 and organic peroxides. The results presented here focus on the H2O2 measurements. Measured concentrations and fluxes show a clear diurnal cycle. The fluxes were mainly downward with deposition velocities of about 4 ± 1 cm s-1. However, upward fluxes (emission) were also observed. These measurements were made in order to determine the importance of the ozonolysis reaction for the H2O2 surface exchanges.
Session 6, Chemical Processes and Dispersion
Tuesday, 16 July 2002, 10:30 AM-12:30 PM
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