Measurements of the dry deposition of peroxides to a Canadian boreal forest

Abstract

The dry deposition rates of hydrogen peroxide (H2O2) and total organic peroxides (ROOH) were measured above a coniferous forest in Saskatchewan, Canada. Deposition velocities νd were obtained from gradient measurements using the modified Bowen ratio method. A diurnal pattern was observed, with highest deposition velocities occurring during the day. Daytime deposition velocities were approximately 5 cm s−1 for H2O2 and 1.6 cm s−1 for ROOH. Nighttime deposition velocities were much smaller, approximately 1 and 0.5 cm s−1, respectively. A slight seasonal trend observed in νd can be attributed to meteorological rather than physiological factors. The seasonal variation of H2O2 and ROOH concentrations, however, effects a significant seasonal variation in flux. Highest concentrations and therefore highest fluxes were observed during midsummer. On a diurnal scale, maximum deposition velocities coincide with high concentrations only during midday. Thus the highest fluxes occur primarily from 1100 to 1500 hours. The transport of H2O2 appears to be similar to that of other soluble, reactive trace gases, such as HNO3 and NH3, and a small surface resistance is suspected.