Particle-size resolved aerosol levels of total and extractable platinum in urban and rural regions of Western Europe

Abstract

In this study, we determined the levels of total and extractable platinum in size-resolved atmospheric aerosol (PM) samples obtained from roadside and background urban sites in each of six European cities (Amsterdam, Frankfurt, London, Milan, Stockholm, and Thessaloniki), as well as at three rural sites in northern, central and southern Europe. A Hi-Vol sampler was used to collect PM in three size classes (PM>7, PM7-3, PM3) which were characterized for total platinum and extractable platinum, using a suite of physiologically relevant extraction fluids – alveolar lung fluid (ALF), gambles saline, 0.07M HCl, and MQ (high purity, 18MΩ, water). The resulting large data set of Pt in ambient aerosols is one of the most extensive developed to date.Order-of-magnitude differences in air concentrations of total platinum were observed between urban sites, ranging from 2.4 to 45.6 pg/m3. Relatively consistent and low concentrations (0.9–4.9 pg/m3) of total platinum were observed at the rural background sites. Roadside canyon sites in London and Thessaloniki exhibited the highest concentrations. Levels of total platinum at urban background sites were similar across the cities (2.4–14.2 pg/m3) and were approximately ½ the levels measured at urban roadside/canyon sites. When total platinum concentrations were normalized to PM mass the range in air concentrations was substantially reduced to just 4-fold (mean of 129 ng/g at rural background sites to 532 ng/g, London/Thessaloniki). The majority of the total platinum was present in the fine (PM3) fraction, however the contribution of coarse particles (>7 μm and 7-3 μm) to total platinum was also very significant (>30% at nearly all sites).Median site class extractable platinum concentrations (total suspended particulate, TSP) were all below 1 pg/m3 except for the urban canyon sites in London and Thessaloniki (1.8–6.8 pg/m3). Rural background concentrations of extractable platinum (TSP) were especially low (0.05 pg/m3 in MQ and 0.13–0.25 pg/m3 in the other solvents). For the TSP, the MQ extractable fraction was 2.5–5.5% of total platinum across site classes and 6.1–21.1% across site classes for the other three solvents. Except for the most contaminated urban canyon sites (London and Thessaloniki) the differences in platinum extracted by the three non-MQ solvents was not significant when site class medians are compared; thus, 0.07M HCl may be used to address the putatively bioaccessible fraction of platinum in aerosol particulate matter.