Long term atmospheric deposition wet-dry fluxes. Critical loads exceedences in an urban area

The present work provides an overview of the most relevant results concerni ng a five years monitoring programme of wet and dry deposition (1995-1999) in the city of Bologna. The aim of this research is to get an overall pictu re of atmospheric pollutants deposition inventory in an urban territory and to allow an assessment of the vulnerability of the area by comparing actua l fluxes of acidity and nutrient nitrogen with the respective "critical loa ds" associated to the territory, in the framework of the UNECE LRTAP (Long Range Transboundary Air Pollution Convention), This comparison, for the Bol ogna monitoring station, shows "exceedance classes" from 4 to 6 for acidity and from 1 to 5 for nutrient nitrogen, reflecting an urban-industrial cont ext, though a trend in reducing occurs from 1995 to 1999. A water layer sur face sampler (DAS-MTX sampler) was employed for "surrogate" dry deposition collection. The contribute of dry fraction to the total deposition fluxes a ppears to prevail on wet fraction for many pollutants (up to more than 90% for total calcium and alkalinity). A comparison with long term monitoring r esults from some stations in Italian territory, shows that the differences among chemical species deposition fluxes may be ascribed both to the long d istance aerial transport of pollutants and to site characteristics.