The Landes experiment - biosphere-atmosphere exchanges of ozone and aerosol-particles above a pine forest

Abstract : An experiment was conducted in a pine forest in southwestern France during late spring 1992. The aim was fourfold: testing various flux measurement methodologies for chemically reactive species; quantifying the exchanges between the forest and the atmosphere; analyzing the involved mechanisms; and studying their influence on the chemistry of the surface boundary layer. This paper presents preliminary results obtained on the dry deposition of ozone and submicronic aerosol particles, measured using eddy correlation. Once properly normalized, the spectra and cospectra of all scalar species exhibit universal shapes over the whole frequency range. However, evidence is provided that under some meteorological conditions the time series of turbulent variables can be affected by nonstationary trends, or low-frequency fluctuations that do not contribute to vertical transfer but whose presence can induce large errors in the calculated fluxes. The time variations of the deposition velocities for ozone and aerosol particles are then presented over 2 days with different meteorological conditions. The deposition velocities are shown to be consistent with other reported studies. Dry deposition of ozone appears to be mainly governed by the stomatal resistance, whereas friction velocity and atmospheric instability in the boundary layer seem to govern the deposition of aerosol particles.