Eddy covariance measurements of ozone flux above and below a southern subtropical forest canopy

While extensive eddy covariance (EC) measurements of ozone (O 3 ) flux have been reported in American and European forests, such measurements in Asian forests are scarce. Here, we presented the first EC measurements of O 3 flux at two levels (above and below the canopy) in a Chinese forest. Above the canopy, O 3 always moved downward, with a maximum O 3 flux intensity of −15 ~ −10 nmol m −2 s −1 occurring at 9:00–14:00 LT and a maximum O 3 deposition velocity of 1.23 cm s −1 occurring at 9:00 LT; both of these values fell to nearly 0 at night. The O 3 deposition flux and O 3 deposition velocity below the canopy were both lower than those above the canopy. This discrepancy reached the maximum at 9:00–15:00 local time (LT), with the O 3 deposition flux and O 3 deposition velocity below the canopy being approximately 35 and 42% of those above the canopy, respectively. The O 3 flux was well correlated with the CO 2 flux and the latent heat flux, suggesting the important role of stomatal uptake in O 3 deposition. The O 3 deposition velocity increased with the increase in the air temperature, relative humidity, photosynthetically active radiation and friction velocity, but when these meteorological factors exceeded their optimum values, the increase in the O 3 deposition velocity tended to be flat. These findings advanced our understanding of the interactions between forests and the atmosphere. This unique dataset is also of great significance for the validation of relevant models concerned with the various impacts of the rapid increase in global O 3 concentrations. • The O 3 flux below the canopy is less than half of that above the canopy. • There are significant correlations between the V d and meteorological factors at both canopy levels. • The relationship between the O 3 flux and CO 2 flux suggests the important role of stomatal uptake.