An experimental study on the planetary boundary layer transport of air pollutants over East Germany

The transport of atmospheric pollutants in the planetary boundary layer over East Germany was studied during the SADE-94 experiment using airborne and ground-based observations of meteorological and chemical parameters. Strong jump-like changes of the SO2 and NOx mixing ratios measured at Melpitz, a rural site about 50 km northeast and 90 km west of two major lignite-coal mining and industrial areas, demonstrate the influence of high emissions and mesoscale transport on the air quality at a rural location. Data of two days with prevailing winds from east and southwest, respectively, were used to determine the origin of plumes from their characteristic species or their specific trace gas concentration ratios. An attempt has been made to establish emitter-receptor relationships between the emittants and the measured plumes of SO2 and NOx. It is shown that not only in complex terrain, where trace gas dispersion is guided in many cases by the terrain structure but also over flat country sites the trace gases of single-point sources are traceable over distances of more than 100 km in the PBL. Furthermore 75 km downstream the source area surface concentrations of air pollutants caused by downdrafts are measured, which exceed 25% of the value registered direct in the lee of the source. Data of a third day describe the mixing ratio of air pollutants in the convective boundary layer at Melpitz. NOx and SO2 are used to depict bottom-up and top-down mixing processes mainly in the entrainment zone. Under low-wind conditions, neutral or stable PBL and a capping inversion single air pollution plumes are detectable over long ranges in time (>6 h) and space (>100 km) over flat terrain. The characteristic features of the plumes keep unchanged during transport. So high stacks only displace the problem of near-surface air pollution from the source region to areas far downstream. (C) 2000 Elsevier Science Ltd. All rights reserved.