RESPONSE OF A GRASSLAND ECOSYSTEM TO AIR-POLLUTANTS .2. THE CHEMICAL CLIMATE - FLUXES OF SEDIMENTING AIRBORNE MATTER

Measurement of the deposition of sedimenting particles requires a sampling device, which avoids simultaneous deposition of gases and aerosols to the collection surface. A sampler constructed for the purpose of collecting rain and sedimenting particles is described and characterized in detail, in particular with regard to its collection efficiency for rain. Its collection properties for gases and aerosols are shown to be negligible. From two years of sampling al different heights it was found that resuspension of particles and co-condensation of gases near the plant canopy may lead to a major overestimation of bulk deposition. As a consequence, the extention towards the canopy of the constant flux layer for sedimenting particles has to be determined experimentally. Bulk deposition of sodium, potassium, magnesium, calcium, lead, copper, cadmium, manganese, iron, ammonium, nitrate, phosphate, sulfate, total sulfur and chloride at Braunschweig-Volkenrode, Southeast Lower Saxony, Germany, were recorded for six years. During this period a considerable decrease was observed in the deposition of lead, cadmium, nitrate, sulfate and total sulfur.