Measuring and Modeling Wet Deposition Fluxes in the Netherlands and Europe

Abstract

The Dutch National Precipitation Chemistry Monitoring Network measures the wet deposition fluxes of acidifying and eutrophying compounds and heavy metals over the Netherlands since 1978. Recent measurements of sulfate, ammonium and nitrate of this precipitation network are used to validate the outcome of the new wet deposition module implemented into the regional air quality model LOTOS-EUROS. The old wet deposition module only included below-cloud scavenging, whereas the new wet deposition module takes into account below-cloud and in-cloud scavenging. Both processes are implemented such that the effect of the saturation of rain droplets on the scavenging efficiency is included. A simple parameterization, based on the liquid water content data from ECMWF, is used to distinguish between regions in which respectively below-cloud or in-cloud scavenging occurs. In general, it is found that the combination of below-cloud and in-cloud scavenging increases the net scavenging process in the LOTOS-EUROS model simulations; hence the wet deposition fluxes are increased. These increased wet deposition fluxes in the model simulations are evaluated at the sites of the precipitation network in the Netherlands and show a better agreement as compared to results of simulations performed with the old wet deposition module. Finally the wet deposition fluxes are also evaluated at the sites of the European EMEP monitoring stations: a similar improvement is found again between the measurements and model results.