A multi-element mapping approach for size-segregated atmospheric particles using laser ablation ICP-MS combined with image analysis.

This is a first attempt to measure the elemental mass loading in size-segregated aerosol particles using a laser ablation ICP-MS mapping approach in combination with image analysis software. For optimal mapping of impaction spots on foils the laser ablation ICP-MS parameters resolution, sensitivity and analysis time were critically balanced, depending on the size of the particles and the mass loading. It was shown that size-segregated particles originating from industry-influenced or urban areas could be visualized (shades of gray or "pseudocolours" representing mass loading) and digitally analyzed by comparison with a commercially available air particulate SRM (NIST 2783). Actual results for industry-influenced and urban aerosol particles show distribution profiles that are similar to these obtained with a conventional wet-chemical leaching approach (with ICP-OES or ICP-MS analysis). Also the mass loadings were in the same range although with whole-spot laser ablation ICP-MS analysis even elemental concentrations in nanoparticles could be measured whereas the leaching approach had insufficient sensitivity to measure these particles. Contrary to the use of single line or crater laser ablation ICP-MS as sometimes practiced in the literature it was found essential to map whole impaction spots due to artifacts generated by cascade impactor sampling, leading to distorted impaction spots (presence of halos or satellites).