The trace metal signature of atmospheric aerosols sampled at a European regional background site (puy de Dôme, France)

Abstract

Trace metal composition of atmospheric aerosols provides clues as to emission sources and history of air masses. Atmospheric trace metal concentrations measured between 2011 and 2013 at puy de Dome (1,465 m elevation, central France) are, on average, intermediate between low-altitude urban sites and Atlantic remote environment (115 ng/m3 Al, 0.55 ng/m3 Sr, 0.136 ng/m3 Ce, 1.34 ng/m3 Pb). Three main factors control trace metal variability: (1) the concentrations markedly decrease at night while the site is generally located in the free troposphere/nocturnal residual layer (average of 43 ng/m3 Al, 0.27 ng/m3 Sr, 0.052 ng/m3 Ce, 0.25 ng/m3 Pb during 2012 summer nights). The nocturnal depletion is greater for refractory crustal elements (Al, Fe, Ti and rare earth elements) than for B, Na and chalcophile/siderophile elements (e.g., Tl, In, Sb, Zn, Cd, Cu, Bi, Mo, Re, Pt and Pd), which probably partition into the gas phase and/or a fine mode fraction. (2) Cr, Ni, Mo, Ag, Pb and Pt record a greater influence of anthropogenic sources (combustion, iron/steel industry, and automobile exhaust catalysts) in winter, and/or in the continental air mass that most frequently influences the site during the cold season. (3) Air masses reaching the site have distinct trace element fingerprints depending on their origin. The African air has crustal like signatures (Al/Ti, La/Sm). The Atlantic air is enriched in B, Cu, Bi, Co, W, Re and Ag and depleted in Tl, Sb and Se relatively to Al. Continental air is enriched in Cr and Ni and depleted in Na. Local air (France) is enriched in chalcophile elements (Zn, Pb, Se, As, Sb, Tl) and to a lesser extent in alkalis and rare earth elements, likely due to limited activation and scavenging of primary particles during a short-history of transport.