Chemical characterization of PM1 at a regional background site in the Western Mediterranean

Abstract

From February 2011 to September 2012, PM1 samples were collected at the regional background station of Mt. Aitana, located near the eastern coast of the Iberian Peninsula at 1558 m a.s.l. Samples were subsequently analyzed to determine the major chemical composition (elemental and organic carbon, secondary inorganic ions and oxalate). The seasonal patterns of the concentrations of PM1 and its main components and the influence of long-range transport of dust from the Sahara desert were studied in this work. PM1 was mainly composed of organic matter and ammonium sulfate, while EC and nitrate were minor components. Concentrations ranged from 3.4 µg m-3 in winter to 5.8 µg m-3 during summer. This seasonal cycle is typical of high mountain sites, which are generally above the planetary boundary layer during winter time. All the analyzed components exhibited the same seasonal pattern except nitrate, which showed minimum values in summer. This is most likely the result of the decomposition of NH4NO3 favored by the higher summer temperatures. Due to the close proximity to the African continent, PM1 levels significantly increased during Saharan dust intrusions. The concentrations of sulfate were 35% higher during dust events since the formation of secondary ammonium sulfate is favored by heterogeneous reactions on the surface of mineral particles.