Heterogeneous chemistry between PbSO4 and calcite microparticles using Raman microimaging

Currently, the smelting activities of lead and zinc are the loudest sources of local pollution by emission in the troposphere of dust of micrometer size containing PbSO4. As the particles evolve in the troposphere, their chemical and physical properties – and hence their characteristics such as toxicity – change by accumulation of atmospheric heterogeneous reactions. Calcite (CaCO3) represents a large part of the mineral fraction in tropospheric aerosols with aerodynamic diameters less than 10 μm. The calcite particles are expected to react with PbSO4 particles. In an effort to model the chemical behaviour of PbSO4 individual particles in the troposphere, we present the in situ Raman imaging results during the course of the reactions in a water droplet of PbSO4 particles with a calcite microcrystal surface. The computer-microcontrolled XY scanning and Z focusing of confocal Raman imaging combined with multivariate curve resolution (MCR) of Raman images have resolved the severe spectral overlaps of the Raman spectra which are not resolved by the spatial resolution of the instrument (∼1 μm3). The results pointed out the identification and the mapping of Pb3(CO3)2(OH)2, PbCO3 and CaSO4·2H2O (gypsum) on the calcite surface.