Chemical characteristics of atmospheric bulk deposition in a semi-rural area of the Po Valley (Italy)

• Published in: Journal of atmospheric chemistry Vol. 75; no. 1; pp. 97 - 121
• Main Authors: Tositti, Laura, Pieri, Linda, Brattich, Erika, Parmeggiani, Silvia, Ventura, Francesca
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.03.2018; Springer Nature B.V
• Subjects: Ammonium; Ammonium compounds; Atmospheric Protection/Air Quality Control/Air Pollution; Atmospheric Sciences; Bicarbonates; Calcium; Calcium ions; Carbonates; Chemical speciation; Deposition; Earth and Environmental Science; Earth Sciences; Fertilization; Industrialization; Ions; Long-range transport; Magnesium; Nitrates; Nitrogen dioxide; Particulate matter; Pollutant deposition; Pollutants; Pollution monitoring; Pollution sources; Precipitation; Precipitation chemistry; Precipitation composition; Resuspension; Rural areas; Soil; Soil mechanics; Stagnation; Statistical analysis; Statistical methods; Sulphates; Trajectory analysis; Urbanization; Italy; Po Valley; pH; Chemical elements; Multivariate analysis; Bulk deposition; Back-trajectory analysis
• ISSN: 0167-7764; 1573-0662
• DOI: 10.1007/s10874-017-9365-9

This study provides an analysis of a five-year time series chemical composition of the bulk deposition (2009–2013), collected within a farm surrounded by industrial and urban settlements in a semi-rural area of the Po Valley, with the aim of characterizing potential emission sources affecting precipitation composition at the site. Most monitoring efforts in this region, recognized as one of the most polluted in the world both due to the intense industrialisation and urbanisation as well as to frequent air stagnation conditions, are presently devoted more to gaseous and particulate pollutants than to precipitation chemistry. The bulk deposition samples were very concentrated in chemical species, both acidic and alkaline, high compared to other polluted sites in the world and to locations in the same district. The mean ions concentrations (in μeq l −1 ) are: NO 3 − (243) > SO 4 2− (220) > PO 4 3− (176) > Cl − (153) > NO 2 − (29) > F − (2.6); NH 4 + (504) > Ca 2+ (489) > K + (151) > Na + (127) > Mg 2+ (127). pH data shows a trend toward slightly alkaline conditions attributed to the large presence of ammonium and crustal elements, in spite of high concentrations of nitrates and sulphates. The relevant concentrations of Ca 2+ and Mg 2+ further suggests that these alkaline conditions might be due to the correspondingly significant concentrations of carbonates/bicarbonates in our dataset. While back-trajectories analysis suggests the stronger importance of local resuspension over long-range transport, statistical analyses on ion composition highlight the key role exerted by agricultural activity, especially in the case of NH 4 + , K + , Ca 2+ and PO 4 3− (especially linked to fertilisation practices and soil resuspension due to mechanical operations). Apart from Na + and Cl − ions which correlate well as expected, indicating their likely common origin from marine salt, the identification of the origin of the other ions is very complex due to the contribution of diverse local sources, such as industrial and residential settlements.