Bulk Atmospheric Deposition in the Southern Po Valley (Northern Italy)

A study on pH and chemical composition of precipitation was carried out in two Italian sites, one urban (site 1) and one rural (site 2), located approximately 30 km far from Bologna, during a 3-year period. No significative site variation was found. In both locations, bulk deposition pH ranged from slightly acid to slightly alkaline, despite the volume weighted mean concentration of acidic species, NO3− and SO42− (67.4 and 118.4 μeq l−1 in site 1 and 88.7 and 103.8 μeq l−1 in site 2), that were similar to those of typical acidic rainfall region. This might be ascribed to the neutralization reaction of the Ca2+, attributed to the calcareous soil and the frequent dusty air mass intrusion from the Sahara. The pair correlation matrix and the analysis of the main components suggested also ammonium and other crustal elements as neutralization agents. The depositional rate of SO42− and NO3−, chemical elements of agricultural interest, amounted to 38 and 28 and 32 and 35 kg ha−1 for site 1 and site 2, respectively. These supplies of nutrient were not negligible and had to be considered on cultivated lands. NH4+ deposition rate on site 2 was 7 kg ha−1, 23% over site 1, probably due to nitrogen fertilization in the fields around the monitoring station. In site 1, SO42− presented a seasonal trend, indicating that its principal source was the residential heating. Results emphasized that the entity of the bulk deposition acidification is linked not only to the ions local emission sources (fossil fuel combustions, heating, and fertilizers) but also to the surrounding territory and the prevalent wind that transports through kilometers air masses which may contain acidic and alkaline species