Aerosol Phosphorus Composition: New Insights from Synchrotron X-ray Spectroscopy

Thursday, 18 December 2014
Amelia Longo1, Ellery D Ingall1, Julia M Diaz2, Michelle M Oakes3, Laura King1, Athanasios Nenes1, Nikolaos Mihalopoulos4, Kaliopi Violaki4, Anna Avila5, Claudia R Benitez-Nelson6, Jay A. Brandes7, Ian McNulty8 and David Vine8, (1)Georgia Institute of Technology, Atlanta, GA, United States, (2)Woods Hole Science Center Woods Hole, Woods Hole, MA, United States, (3)Environmental Protection Agency Research Triangle Park, Research Triangle Park, NC, United States, (4)University of Crete, Heraklion, Greece, (5)Universitat de Barcelona, Barcelona, Spain, (6)Univ South Carolina, Columbia, SC, United States, (7)Skidaway Institute of Oceanography, Savannah, GA, United States, (8)Argonne National Laboratory, Argonne, IL, United States
Biological productivity in many ocean regions is controlled by the availability of the nutrient phosphorus (P), including the eastern Mediterranean Sea. Aerosol deposition is a key source of P in the Mediterranean. Understanding the composition of this P is critical for determining its solubility and therefore potential bioavailability. We investigated aerosol P composition in European and North African air masses, the main sources of aerosol deposition to the Mediterranean Sea, using Phosphorus Near Edge X-ray Fluorescence Spectroscopy (P-NEXFS). We show that European aerosols are a significant source of soluble P to the Mediterranean Sea. The traditionally studied North African sourced air masses carry more total P to the Mediterranean Sea than European sourced air masses and contain mostly apatite, a largely insoluble calcium phosphate mineral. However, European aerosols deliver P that is on average 3.5 times more soluble than North African aerosols and furthermore are dominated by organic P compounds. The increased solubility of European aerosols leads to comparable amounts of soluble P by mass delivered to the Mediterranean Sea by both air masses. The ultimate origin of organic P does not stem from common primary emission sources, such as coal fly ash and diesel emissions. Rather, P associated with bacteria best explains the presence of organic P in Mediterranean aerosols. The soluble organic nature of the P in European sourced air masses underscores the need to examine aerosols from this region as a source of P to the Mediterranean Sea. This study also demonstrates that synchrotron-based techniques are effective tools for characterizing aerosols and gaining new insights.