Abstract
Concentrations of 33 metal elements were determined by ICP-MS (Inductively Coupled Plasma Mass Spectrometry) analysis for 24 cloud water samples (corresponding to 10 cloud events) collected at the puy de Dôme station. Clouds present contrasted chemical composition with mainly marine and continental characteristics; for some cloud events, a further anthropogenic source can be superimposed on the background level. In this context, measurements of trace metals may help to evaluate the impact of anthropogenic and natural sources on the cloud and to better discriminate the origin of the air masses. The metal concentrations in the samples are low (between 16.4 µg L−1 and 1.46 mg L−1). This could be explained by the remoteness of the puy de Dôme site from local sources. Trace metals are then used to confirm and refine a previous sample classification. A principal component analysis (PCA) using the pH value and the concentrations of Cl−, NO3−, SO42−, Na+ and NH4+ is performed considering 24 cloud samples. This first analysis shows that 18 samples are of marine origin and 6 samples are classified as continental. The same statistical approach is used adding trace metal concentration. Zn and Mg elements are the most abundant trace metals for all clouds. A higher concentration of Cd is mainly associated to clouds from marine origins. Cu, As, Tl and Sb elements are rather found in the continental samples than in the marine ones. Mg, V, Mn and Rb elements mainly found in soil particles are also more concentrated in the samples from continental air mass. This new PCA including trace metal confirms the classification between marine and continental air masses but also indicates that one sample presenting low pH and high concentrations of SO42−, Fe, Pb and Cu could be rather attributed to a polluted event.
Highlights
Clouds contain a myriad of inorganic and organic compounds resulting from the dissolution of aerosol particles acting as Cloud Condensation Nuclei (CCN) and from the mass transfer of chemical species from the gas to the aqueous phase depending on their solubility
Arsenic (As) concentrations in cloud waters collected at the puy de Dôme site from marine and continental origins are low and are comparable to those reported for References [5,13,14,16,37], whereas References [15,38] which are related to polluted sampling sites, show concentrations 15–20 times higher
Mn and Fe in both continental and marine origin samples presented in this work show low concentrations: this is probably due to the fact that these trace metals are mostly insoluble when they come from crustal particles, while they are more soluble if adsorbed in carbonaceous aerosol, associated with anthropogenic emissions
Summary
Clouds contain a myriad of inorganic and organic compounds resulting from the dissolution of aerosol particles acting as Cloud Condensation Nuclei (CCN) and from the mass transfer of chemical species from the gas to the aqueous phase depending on their solubility. Among these compounds, trace metal elements are present in atmospheric waters (rain, snow, fog and cloud droplets) in low concentration (from mg to μg L−1 ) and result essentially from particle dissolution. The redox cycle of dissolved trace metals plays an important role on cloud water reactivity Numerous parameters such as the oxidation state, the complexation and pH, influence the reactivity of transition metals.
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