Towards development of a deposition monitoring network for air pollution of Europe (LIFE II)

The interpretation of the flux measurements at the Speulder forest should lead to:

• primary wet and dry deposition fluxes of the measured components
• yearly averaged fluxes

These fluxes should serve as a reference method for newly designed monitoring systems that can be applied on many locations for a reasonable price. Furthermore the deposition characteristics at one of the three core-sites: Speuld for the RIVM should be determined and the measured fluxes should be used for improvement and further evaluation of the deposition models. The gradient measurements were subjected to a selection to comply with the conditions of the flux gradient method and to be able to determine fluxes accurately.

Each year, less valid hours remain, caused by a decrease in concentrations (SO₂) and increasing instrumental failure (NH₃). The dry deposition flux of NH₃ was extremely high in 1997 (2729 mol/ha/yr), probably caused by extremes in the measurements. The new dry deposition velocity parameterisations of NH₃ (by TNO) is capable of producing emission fluxes during periods of low ambient NH₃ concentrations, through the incorporation of the compensation point. It can be seen that this parameterisation is better, although negative measured fluxes (emission fluxes) are still not reproduced very well. The quality of the measurements was not high enough to extract new parameterisations or to validate older concepts like co-deposition or even enhanced deposition at wet leaf surfaces.