Heterogeneity of platinum group metals in airborne particles

The emission of three of the platinum group metals (PGMs), Pd, Pt, and Rh, from automobile catalysts and into the urban environment is a potential concern for human health. The analysis of low concentrations of PGMs in air particles is an analytical challenge, and it is demonstrated that interferences in inductively coupled plasma-mass spectrometry (ICP-MS) can be corrected mathematically for Pt and Rh and, at higher concentrations, for Pd. The PM10 concentrations of PGMs in urban air collected in Göteborg are 0.1-10 pg m-3 (Pd), 0.9-19 pg m-3 (Pt), and 0.3-4 pg m-3 (Rh), with higher values for greater traffic intensity. These concentrations provide a general background for the urban atmospheric environment, and the Pt:Rh ratio (4.2:1) agrees with known automobile catalyst composition. The analysis of filters from 10 parallel samplers indicated the significant heterogeneity of PGMs in samples of urban air particles. Scanning laser ablation ICP-MS provided the micron spatial resolution required to identify individual particles. Ablation across the filter surface demonstrated the presence of relatively few particles with a high concentration of PGMs. These occasional high concentration particles, which might be overlooked in conventional air sampling with total analysis, have a high Pt:Rh ratio (12.3:1), which can be attributed to catalyst aging during vehicle operation.