PROFILES AND SIMULATED EXCHANGE OF H2O, O-3, NO2 BETWEEN THE ATMOSPHERE AND THE HARTX SCOTS PINE PLANTATION

Vertical profiles of H2O, CO2, O-3, NO and NO2 were measured during th e Hartheim Experiment (HartX) to develop and calibrate a multi-layer r esistance model to estimate deposition and emission of the cited gaseo us species. The meteorological and gas concentration data were obtaine d with a 30 m high telescopic mast with 7 gas inlets located at 5 m in tervals and meteorological sensors at 5, 15 and 30 m above ground; a c omplete gas profile was obtained every 9 min 20 s. Measured profiles w ere influenced by several exchange processes, namely evapotranspiratio n, dewfall, assimilation of CO2 in the tree crowns, soil respiration, deposition of NO2 and O-3 to the soil and advection of NOx from the ne arby highway. Surprisingly, no decrease in O-3 concentration was obser ved in the crown layer during daytime, probably due to the relatively low density of foliage elements and strong turbulent mixing. The advan tage of measuring in-canopy profiles is that turbulent exchange coeffi cients need not be estimated as a prerequisite to obtaining vertical f lux estimates. In recent years, flux-gradient relationships in canopie s have been subject to many criticisms. If fluxes are calculated at se veral heights considering only the transfers between the turbulent air and the interacting surfaces at a certain height, and those fluxes ar e then integrated vertically in a subsequent step, then exchange estim ates (deposition or emission) can be obtained independent of turbulent exchange conditions. Typical estimated deposition velocities calculat ed for a 3-day period are between 4 and 10 mm/s for NO2 and about 4-9 mm/s for O-3 (day and night values respectively). This leads to deposi tion rates of about 20-40 ng N/m(2)s for NO2 and about 30-40 mg O-3/m( 2) deposited daily under the conditions encountered during HartX. Sens itivity tests done with the best available and most realistic values f or model parametrization have shown that sensitivity is large with res pect to the soil and cuticula resistances as well as for gas-phase ozo ne destruction and that more research is required to describe the effe ctiveness of cuticula and soil in modifying sink characteristics for N O2 and O-3.