Ozone Fluxes Over a Boreal Lake Exhibit Enhanced Deposition at Nights

A few studies on ozone deposition over lake water are available and so far only one using the eddy covariance technique (Wesely et al., 1981, ). A 23-day field campaign was held in August-September 2012 at the Lake Kuivajarvi in Hyytiala, Finland. The results showed a mean flux of -30 +/- 1 ng m-2 s-1 and deposition velocity of 0.86 +/- 0.05 mm s-1. Deposition velocity showed a weak diurnal cycle over the lake with elevated values during the nighttime. The daytime and nighttime portions of the data set differed statistically. Analysis showed that waterside convective mixing enhanced deposition and such conditions pre-dominantly occurred during nighttime. We compared the measured deposition velocities with the dry deposition model of air-sea exchange, adjusted for the chemical sinks relevant for the lake. We suggest that the buoyant mixing and unaccounted chemistry can be responsible for the difference between the model results and observations. Ozone deposition was studied over lake in Southern Finland. Deposition velocity showed elevated values during the nighttime. Higher ozone deposition at night was related to enhanced convective mixing in uppermost water layers. Ozone deposition over the lake is enhanced by waterside buoyancy velocityWind speed and friction velocity had minor or no impact on ozone deposition, instead waterside convective mixing enhanced depositionIn late summer, over diurnal course higher deposition velocities occurred at night

Automated summary

This study investigated ozone deposition over lakes in Finland using the eddy covariance technique. The results showed that ozone deposition velocity was higher during nighttime, which was related to enhanced convective mixing in the uppermost water layers. Waterside convective mixing enhanced ozone deposition, while wind speed and friction velocity had minor impacts on deposition.