Airborne suspended particulate matter can be of primary origin, . emitted directly into the atmosphere or of secondary origin, . formed in the atmosphere from gaseous species by either homogeneous or heterogeneous chemical reactions. Due to these different emission sources, particles have different chemical composition and size distributions. Depending on their size, particles have a different potential to be transported over either long or short distances [1]. Primary particles can be produced from either natural or anthropogenic sources. In Europe the main natural sources are sea spray [2] and soil resuspension by wind [3]. Also, in the Mediterranean basin, Saharan dust [4] and volcano emissions [5].
