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

The dry deposition rates of hydrogen peroxide (H 2 O 2 ) and total organic peroxides (ROOH) were measured above a coniferous forest in Saskatchewan, Canada. Deposition velocities ν d 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 H 2 O 2 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 ν d can be attributed to meteorological rather than physiological factors. The seasonal variation of H 2 O 2 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 H 2 O 2 appears to be similar to that of other soluble, reactive trace gases, such as HNO 3 and NH 3 , and a small surface resistance is suspected.