Mixing mechanisms of lead nanoparticles with mineral particles: implication of atmospheric transportation of lead

Abstract

Atmospheric mixing particles play a significant role in the ecosystem but is poorly quantified for the effect on climate and air quality, especially for the mixing of sand dust (mineral particles) and anthropogenic pollution (heavy metals) over East Asia. Hence, by combining molecular dynamics (MD) simulations and density functional theory (DFT) calculations, we investigated the mixing mechanisms of typical Pb nanoparticles (PbO, PbSO₄, PbCO₃, PbCl₂ and PbS) with sand and dust (SD) particles (Al₂O₃) in the atmosphere. Our MD simulations show that five target Pb nanoparticles get rapidly mixed with Al₂O₃ and are then retained on the surface, with three interfacial patterns of monodentate, bidentate and tridentate modes according to the interaction form of Pb atoms with Al₂O₃. Further DFT calculations reveal that the mixing ability of the oxygenated Pb nanoparticles with Al₂O₃ depends on the distances of Pb nanoparticles with the Al₂O₃ surface and the lengths of short hydrogen bonds; however, for non-oxygenated Pb nanoparticles, it is relevant to the length of long hydrogen bonds. Chemical bonding analyses show that after mixing, the interaction strength of Pb particles with Al₂O₃ follows the order of tridentate > bidentate > monodentate modes. The diffusion coefficients of mixed Pb nanoparticles are significantly lower than those of the unmixed Pb particles, resulting in stabilization, and the mixed oxygenated Pb nanoparticles are more stable than non-oxygenated Pb nanoparticles. Our results highlight the important role of SD particles in the capture and restriction of Pb nanoparticles and the necessity to account for the potential transport route of Pb nanoparticles with SD particles.