Dry deposition monitoring over the Speulder forest. Description of the equipment and evaluation of the measuring methods

A detailed error analysis of the gas and particle fluxes derived from the data of the system, and some recommendations for final improvements and flux correction procedures are given as well. The error analysis shows that fluxes of SO₂, NH₃ and NO can be determined with acceptable accuracy. Systematic errors for NO_x and NO₂ are large, yielding on the average about 50 to 100% overestimation of the fluxes. These errors are mainly caused by interferences of HNO₂, HNO₃ and NH₃. In future measurements, the systematic errors can be significantly reduced by correcting friction velocities and sensible heat fluxes for flow distortion, correcting sensible heat fluxes for the influence of moisture flux and horizontal wind velocity, and correcting gas concentrations for pressure effects and interferences.

The latter requires continuous determination of the interferents concentrations and concentration differences; the latter might also be estimated from parameterized deposition velocities. The correction procedures are described in this report. The uncertainties in fluxes of HNO₂, HNO₃ and HCl and particulate compounds were estimated to be 30% for acidic gases, 40% for acidic aerosols and basic cations and 50% for heavy metals. They are mainly a result of uncertainties in parameterized deposition velocities.