Traffic-related platinum and rhodium concentrations in the atmosphere of Rome

Abstract

Platinum and Rh content in the atmosphere of Rome as released by car catalytic converters was monitored from 1998 to 2000 in six urban sites with different traffic intensities and in one rural area. Samples collected with medium-volume PM10 samplers were analyzed by Sector Field Inductively Coupled Plasma Mass Spectrometry (SF-ICP-MS). The Pt content varied from 2.4 to 60.1 pg m⁻³ (mean value 17.8 pg m⁻³) at the urban locations whilst that of Rh spanned the range 0.8–9.4 pg m⁻³ (average value 4.0 pg m⁻³). The rural area showed metal levels mostly below the limits of detection, pointing to automobile traffic as the main source of those elements in the urban atmosphere. The highest mean concentrations of Pt and Rh, i.e. 22.2 and 5.0 pg m⁻³, were detected along the ring road where the traffic density is high (>100,000 vehicles per day) and the driving speed between 100 and 120 km h⁻¹. The lowest Pt and Rh mean concentrations, i.e. 11.4 and 3.4 pg m⁻³, were measured downtown, where traffic density is lower (20,000 vehicles per day) and the driving speed is limited (50 km h⁻¹). Significant concentrations of Pt and Rh were found in the vicinity of traffic signals, indicating that the “stop-and-go” conditions might also affect their release. The measured Pt/Rh ratio spanned the range 3.3–5.9 in accordance with that present in the more commonly used gasoline car catalytic converters. Seasonal variations between wintertime (with Pt and Rh mean concentrations of 23.8 and 5.1 pg m⁻³, respectively) and summertime (with Pt and Rh mean concentrations of 14.1 and 3.3 pg m⁻³, respectively) were also observed.