Calcite deposition from carbonaceous particles scavenged by snow

Abstract

The melting of snow precipitating in an urban area and deposited on an inert substrate (gres) is shown to give rise to the formation of a hard deposit. The deposit is mainly composed of calcium carbonate (CaCO3, 85%) and appears to include components of atmospheric aerosol, such as soot, minerals (silicates, oxides, carbonates) and rock fragments. The carbonaceous particles (soot), which are present in high concentrations, are recognized to be the residual product of oil-combustion processes. The soot has been found to nucleate several crystalline species, among which calcium sulphate bihydrate (gypsum: CaSO4 · 2H2O) is prevalent. Under the particular chemico-physical conditions reported herein, the calcium ion supplied by the soot causes CaCO3 precipitation, while the nucleation of CaSO4 · 2H2O is prevented. Finally, the hypothesis that the calcite found in atmospheric aerosol may partially be of similar origin is advanced. © 1986.