Platinum and rhodium distribution in airborne particulate matter and road dust

In this work the platinum and rhodium content in the atmosphere of Madrid w as monitored for 1 year at seven different sites. Samples were taken with m edium volume PM-10 collectors (<10 <mu>m) for 48 h and analysed by ICP-MS. The Pt and Rh content was dependent on the sampling site, ranging from < 0. 1 to 57.1 and < 0.2 to 12.2 pg m(-3) with a medium value of 12.8 and 3.3 pg m(-3), respectively. These results show that the Pt and Rh content in airb orne samples depends on the traffic density per day and also on medium driv ing speed. Road dust < 63 <mu>m was analysed at the same time and at the sa me location. The Pt and Ph content at the six sites analysed was in the 31- 2252 and 11-182 ng g(-1) range with an average of 317 and 74 ng g(-1), resp ectively. The average Pt/Rh ratio obtained was 4.3, similar to that obtaine d for airborne particles (4.0), and agrees with that of the more commonly u sed gasoline car catalyst [J.J. Mooney, Encyclopaedia of Chemical Technolog y (1996) 982]. Platinum distribution as a function of particle size in airb orne particulate matter was also studied, by sampling with two high-volume sample collectors, a five-stage WRAC(from 10 to 65.3 mum and total) and a s even-stages PM-10 cascade impactor (from 9 to < 0.39 <mu>m) Platinum is ass ociated with a wide range of particle diameters. Due to the ultratrace leve l of Pt in airborne samples, its distribution in the atmosphere could not b e considered as homogeneous. No trend could be established in Pt distributi on in the different fractions, except that in most cases the highest value of Pt was obtained in the < 0.39-<mu>m fraction. The Pt content was usually high in airborne samples when the Pb, Ce, Zr and Hf content was also high, thus confirming that the source of these pollutants is from traffic. (C) 2 001 Elsevier Science B.V. All rights reserved.