TRANSPORT OF POLLUTED BOUNDARY-LAYER AIR FROM THE PO VALLEY TO HIGH-ALPINE SITES

Within the EUROTRAC subproject ALPTRAC the occurrence of reactive trac e species at high-alpine sites was investigated. As a part of these st udies, the transport of boundary layer air from the Po Valley, which i s one potential major source region for air pollution in the Alps, to the high-mountain sites Sonnblick (3106 m) in Austria and Jungfraujoch (3579 m) in Switzerland was studied. A case study based on isentropic trajectories derived from a fine-mesh analysis showed the potential o f such transports to cause substantial peaks in the aerosol concentrat ion at Sonnblick. However, on a climatological basis the Po Valley doe s not seem to cause higher-than-average concentrations of species such as SO2, SO42-, NH4+ and NO3-. Its contribution was estimated to be ab out 15% in summer and much less in winter. Indications of orographical ly induced, subgrid vertical transports were found which are important for the interpretation of data from pollution monitoring programmes a t high-alpine sites. (C) 1998 Elsevier Science Ltd. All rights reserve d.