THE LANDES EXPERIMENT - BIOSPHERE-ATMOSPHERE EXCHANGES OF OZONE AND AEROSOL-PARTICLES ABOVE A PINE FOREST

An experiment was conducted in a pine forest in southwestern France du ring late spring 1992. The aim was fourfold: testing various flux meas urement methodologies for chemically reactive species; quantifying the exchanges between the forest and the atmosphere; analyzing the involv ed mechanisms; and studying their influence on the chemistry of the su rface boundary layer. This paper presents preliminary results obtained on the dry deposition of ozone and submicronic aerosol particles, mea sured using eddy correlation. Once properly normalized, the spectra an d cospectra of all scalar species exhibit universal shapes over the wh ole frequency range. However, evidence is provided that under some met eorological conditions the time series of turbulent variables can be a ffected by nonstationary trends, or low-frequency fluctuations that do not contribute to vertical transfer but whose presence can induce lar ge errors in the calculated fluxes. The time variations of the deposit ion velocities for ozone and aerosol particles are then presented over 2 days with different meteorological conditions. The deposition veloc ities are shown to be consistent with other reported studies. Dry depo sition of ozone appears to be mainly governed by the stomatal resistan ce, whereas friction velocity and atmospheric instability in the bound ary layer seem to govern the deposition of aerosol particles.