Concentration and distribution of heavy metals in urban airborne particulate matter in Frankfurt am Main, Germany

Heavy metal concentrations were measured in airborne dust collected at three sites with different traffic densities from August 2001 to July 2002 in the Frankfurt am Main area. Bulk samples of particulate matter (PM) with an aerodynamic equivalent diameter of <22 microm were collected on cellulose nitrate filters using air filtration devices. Fractionated samples of PM with an aerodynamic equivalent diameter of <10 microm were collected using an eight-stage Andersen impactor. Pb, Cd, Mn, Ni, Zn, V, As, Sb, Cu, Cr, Co, and Ce were determined by inductively coupled plasma sector field mass spectrometry, Pt and Rh were determined by adsorptive voltammetry, and Pd was determined by total reflection X-ray fluorescence analysis. The results show that the highest airborne heavy metal concentrations occurred at the main street with a large volume of traffic. With the exception of Co, V, Ce, and Mn, the heavy metals had an elevated enrichment factor compared to their concentrations in the continental crust. The main street site was especially contaminated with Sb, Zn, Cu, V, and Ni. Motor vehicles are the likely source of emissions. With the exception of Cr, Cu, and Zn, most of the airborne heavy metal concentrations determined for impactor samples deviate slightly from the results for total airborne dust. Heavy metal particle size distributions can be divided into three groups. For metals such as As, Cd, Pb, and V, the main fraction can be found in fine particles with a diameter of <2.1 microm, whereas Ce, Cr, Co, and Ni occur mainly in coarse particles with a diameter of >2.1 microm. Cu, Mn, Sb, Zn, Pt, Pd, and Rh occur in high concentrations in the medium range of the impactor stages (particle diameters of 1.1-4.7 microm). Metal concentrations in fine dust particles are needed to assess the human health risks of their inhalation.     

Changes in palladium, platinum, and rhodium concentrations, and their spatial distribution in soils along a major highway in Germany from 1994 to 2004

Soil samples were collected along the highway A5 from the major junctions Frankfurter Kreuz to Darmst?der Kreuz from July to September, 2004 and analyzed for palladium (Pd), platinum (Pt), and rhodium (Rh). The results were compared to analyses of platinum group elements (PGE) in soils collected along this same stretch of highway in 1994. The goal of this study is to detect any changes that may have occurred in the concentration and environmental distribution patterns of these metals over this 10 year period. The concentrations of Pd in soils along the highway were found to be about 15 times higher on average than those measured in 1994. Pt and Rh concentrations increased 2 and 1.6 times, respectively, during this time period. The significant rise in Pd concentrations in soils observed for the time period of analysis is likely due to its use in automobile catalytic converters in Germany since 1993. The results also show a strong positive relationship between PGE emissions and traffic density and speed. The results indicate that increases in the concentrations of Pd, Pt, and Rh in soils along the highway are not limited to the soil surface. Pt was measured as deep as 12 cm. Pd was determined at even greater depths of 12-16 cm. The presence of Pd at lower depths compared to Pt suggests that this element has a higher solubility. Pd, Pt, and Rh concentrations display a strong inverse relationship with distance from the road, with decreasing levels with increasing distance from the highway. Nonetheless, Pd and Pt were detected in a meadow as far as 50 m from the highway, a much greater distance compared to that measured for these metals in 1994. Pt concentrations were also found to significantly correlate with levels of Rh and Pd. The ratios between the PGE analyzed (Pt/Rh and Pd/Rh) display a shift toward Pt and Pd. The results clearly show that PGE concentrations have increased over time. Observed increases in Pd concentrations are particularly a cause of concern.     

Platinum, palladium, and rhodium in fresh snow from the Aspe Valley (Pyrenees Mountains, France)

Platinum, palladium, and rhodium have been measured in fresh snow samples from 14 locations within the Aspe Valley (Pyrenees Mountains, France) during two winter seasons, February 2003 and March 2004. Ultraclean procedures were employed for the sampling, sample treatment, and analysis in order to reduce sample contamination. Possible spectral interferences on platinum group element (PGE) analysis by inductively coupled plasma mass spectrometry (ICP-MS) were controlled and corrected. The detection limits obtained were 0.05, 0.45, and 0.075 pg g(-1) for Pt, Pd, and Rh, respectively. PGE content in fresh snow from the Pyrenees Mountains range from 0.20 to 2.51 pg g(-1) for Pt, 1.45-14.04 pg g(-1) for Pd, and 0.24-0.66 pg g(-1) for Rh. The higher PGE concentration, generally measured in sites located close to road traffic, exhibit potential resuspension of PGE-enriched particles emitted locally from the car exhaust, although no direct relationship could be observed with the number of vehicles. Measured atmospheric synoptic conditions allowed identification of the origin of air masses reaching the Aspe Valley and therefore provided information about the possible sources of platinum group elements. Higher PGE concentrations measured in 2004 samples, compared to the ones collected in 2003, indicate the influence of atmospheric synoptic conditions on the studied area. Fresh snow samples collected in 2003 could not be linked to a specific source, whereas 2004 samples could be influenced by PGE emissions from European vehicle fleet and Russian PGE-containing mining activities.     

Platinum and rhodium concentrations in airborne particulate matter in Germany from 1988 to 1998

Increases in platinum group element (PGE) concentrations in ambient air and dust since the introduction of automotive catalytic converters in 1988 is a cause of concern. Until now, data derived from engine-test bench experiments have provided the basis for the assessment of human health risks associated with PGE exposure. Such experiments have provided valuable information regarding emission data that has been used to estimate ambient exposure concentrations. However, these data are not necessarily representative of typical environmental PGE exposure levels and conditions. Data on measured environmental concentrations is needed to provide a more adequate basis for the assessment of exposure and related risks. Twenty air and airborne-dust samples were provided by the Umweltbundesamt (Federal Environmental Agency, Germany) in the years 1988, 1989, 1992, 1997, and 1998. The samples were collected in Frankfurt/Main and the adjacent city of Offenbach. For this, 11 to 80 m3 of air were filtered over a 24-72 h period using a vacuum. Glass-fiber filters were used to collect samples. Sample platinum and rhodium concentrations were determined using adsorptive voltammetry. Although the number of samples collected in different years is limited, the results indicate a trend toward continuous increases in ambient concentrations of these metals between 1988 and 1998. Specifically, there were 46- and 27-fold increases in Pt and Rh concentrations, respectively. Despite these observed increases, the Pt concentrations measured (i.e., 147 pg/m3 on average, with a maximum of 246 pg/m3 in 1998) fell far below 15,000 pg/m3, which has been suggested as a guidance value (i.e., exposure at this level would be expected to be without appreciable health risk). The results of a particle-size distribution analysis of one sample (8-step impactor) that was collected 150 m away from a street show that approximately 75% of Pt and 95% of Rh occurs in association with large particulate matter of > 2 microns, with concentrations reaching a maximum in particles of 4.7 to 5.8 microns. The remaining 25% of Pt and 5% of Rh is present in fine particulate matter of < 2 microns. An approximate 10% of Pt and < 38% of Rh in airborne particles was found to be soluble in 0.1 molar HCl. Further, the results indicate that most of the emitted PGE particles from automotive catalytic converters, particularly those bound to fine particulate matter, are capable of being airborne. As a result, PGEs are not only present in areas close to emissions (e.g., roads), but can be transported over longer distances.     

Platinum group element concentrations and osmium isotopic composition in urban airborne particles from Boston, Massachusetts

Platinum, Pd, Rh, and Os were found to occur at elevated concentrations in airborne particles (PM10) collected at urban sites in Boston, MA. Average Pt, Pd, Rh, and Os concentrations were 6.9 +/- 1.9, 8.1 +/- 1.8, 1.50 +/- 0.50, and 0.068 (-0.068 + 0.070) pg m(-3), respectively. Elevated Pt, Pd, and Rh concentrations are attributed to automobile catalysts, which use Pt, Pd, and Rh for the removal of pollutants from engine exhaust gas. An automobile catalyst source is supported by significant correlations between these elements and by a Pt/Rh similar to that in catalysts. Elevated Os concentrations are also believed to be the result of emission from automobile catalysts in which Os occurs as an impurity. The isotopic composition of Os (187Os/ 188Os) ranged from 0.30 to 2.90, indicating large variations in Os sources. Osmium has a predominantly anthropogenic origin at concentrations > 0.1 pg m(-3), whereas natural sources are more important at lower Os concentrations. Osmium isotopic composition also indicates that Pt, Pd, and Rh in Boston air are of almost exclusive anthropogenic origin, with a relatively small natural contribution. Our results indicate that scavenging by rain plays a major role in the atmospheric residence time and environmental fate of PGE.     

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 G?teborg 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.     

Fractionation and reactivity of platinum group elements during estuarine mixing

The fractionation of platinum group elements (PGE) rhodium(III), palladium(II), and platinum(IV), has been studied after their addition in aqueous form to unfiltered river water samples (Tugela river, South Africa) and to mixtures of river water and seawater. The particulate fraction of PGE averaged about 70 (Rh), 50 (Pd), and 25% (Pt) of total metal and was dependent on both particle concentration and salinity. The aqueous (<0.45 microm) pool of PGE was dominated by entities of less than 0.1 microm in diameter, and for Pd and Rh hydrophobic complexes of metal, operationally defined by their retention on a C-18 column, were significant. Distribution coefficients, based on the w/w concentration of metal on particles relative to the corresponding concentration in the aqueous pool, either increased (Rh and Pd) or declined (Pt) with increasing salinity. These observations are interpreted in terms of a number of general and metal-specific mechanisms. Thus, the behavior of Pd appears to be controlled by its association with relatively small (<0.1 microm) dissolved organic ligands, a significant fraction of which is hydrophobic and is subject to salting out upon estuarine mixing. Rhodium may also be partly subject to this mechanism of removal, but kinetic considerations and results of X-ray analysis of filter-retentates suggest that adsorption of cationic hydroxychlorides and the destabilization and precipitation of hydroxy-complexes induced by the rise in pH across the estuarine gradient are more important. Unlike Pd, the binding of Pt by organic ligands is kinetically hindered. Thus, in contrast to Pd, particle-water reactivity of Pt is controlled by electrostatic interactions between the particle surface and inorganic aqueous species. The results of this study improve our understanding of and ability to predict the transport and fate of PGE in estuaries where these metals are mobilized or discharged.     

Temporal and spatial studies of autocatalyst-derived platinum, rhodium, and palladium and selected vehicle-derived trace elements in the environment

The distribution of platinum, rhodium, and palladium (platinum-group elements; PGEs) adjacent to two major U.K. roads shows a rapid decrease (more than 1 order of magnitude) away from the road and reflects patterns shown by other traffic-derived trace elements such as Pb and Zn. However, ratios of Pt:Rh remain relatively constant from 0 to 10 m distance, suggesting that at least some of the PGEs are transported away from the source. A temporal study over a 12-month period, of road dust and surface samples, reveals elevated concentrations above background levels, with maximum values of Pt >500 ng g(-1), Rh 70 ng g(-1), and Pd 70 ng g(-1). Concentrations vary considerably throughout the year and show some tentative correlation with rainfall. Element speciation, an essential control on mobility and hence distribution, was investigated, and the results of solubility experiments show that up to 30% of the Pd present dissolves in acid solutions. This indicates that at least some of the Pd is present in a soluble form and is therefore potentially highly mobile.     

Platinum group elements in airborne particles in Mexico City

Automobile exhaust catalysts using platinum group elements (PGE) have been mandatory on new cars in the Mexico City Metropolitan Area (MCMA) since 1991. Platinum, Pd, Rh, Ir, and Os concentrations and the isotopic composition of Os were determined in PM10 samples from the MCMA. Samples were prepared by isotope dilution NiS fire assay, and analysis was performed by magnetic sector ICP-MS using a single collector instrument for Pt, Pd, Rh, and Ir analysis and a multicollector instrument for Os analysis. Pt, Pd, and Rh concentrations at a downtown location (Merced) increased from < or =1.7 pg of Pt m(-3), 2.7 (4.0) pg of Pd m(-3), and 1.2+/-0.9 pg of Rh m(-3) in 1991 to 9.6 +/- 1.8 pg of Pt m(-3), 10.2+/-1.8 pg of Pd m(-3), and 2.8 +/-0.6 pg of Rh m(-3) in 2003. Concentrations at five sites in MCMA in 2003 averaged 9.3+/-1.9 pg of Pt m(-3), 11+/-4 pg of Pd m(-3), and 3.2+/- 1.0 pg of Rh m(-3). In contrast, Ir and Os concentrations and Os isotopic composition remained relatively constant and were 0.08+/-0.04 pg of Ir m(-3), 0.030 +/-0.007 pg of Os m(-3), and 0.60+/-0.04, respectively, in the MCMA in 2003. Elevated Pt, Pd, and Rh concentrations in the MCMA are attributed to automobile catalysts. A Pt-Pd-Rh concentration peak in 1993 suggests that early catalysts emitted a larger amount of PGE, possibly due to factors inherent in the technology or the use of inappropriate gasoline. Therefore, this study suggests that the current introduction of automobile catalysts in developing countries may result in elevated PGE concentrations if it is not accompanied by infrastructures and policy measures supporting their efficient use.     

Recent changes in platinum group element concentrations and osmium isotopic composition in sediments from an urban lake

Automobile catalyst emissions have resulted in the occurrence of elevated Pt, Pd, and Rh concentration in the urban and roadside environment. We investigate the chronology of platinum group elements (PGE) accumulation in dated sediments from an urban lake near Boston, MA. Chronological profiles demonstrate that Pt, Pd, and Rh concentrations increased following the introduction in catalysts with accumulation rates 6-16 times larger in 1992-2002 than prior to the introduction of catalysts. Ratios of these elements closely match their ratios in catalysts, providing further evidence of an automobile source. Iridium and Ru accumulation in sediments also increased following the introduction of catalysts, and while past Os contamination is associated with leather tanning, recent changes in the isotopic composition of Os indicate another anthropogenic source for this element. The PGE have similar geochemical properties and are difficult to separate from one another, and therefore, we suggest that automobile catalyst emissions also result in increasing environmental concentrations of Ir, Ru, and Os, which occur as impurities in catalysts. An automobile catalyst source of Ir and Os is supported by elevated concentrations of these elements in a tunnel dust sample.     

Measurements of size-segregated emission particles by a sampling system based on the cascade impactor

A special sampling system for measurements of size-segregated particles directly at the source of emission was designed and constructed. The central part of this system is a low-pressure cascade impactor with 10 collection stages for the size ranges between 15 nm and 16 microm. Its capability and suitability was proven by sampling particles atthe stack (100 degrees C) of a coal-fired power station in Slovenia. These measurements showed very reasonable results in comparison with a commercial cascade impactor for PM10 and PM2.5 and with a plane device for total suspended particulate matter (TSP). The best agreement with the measurements made by a commercial impactor was found for concentrations of TSP above 10 mg m(-3), i.e., the average PM2.5/PM10 ratios obtained by a commercial impactor and by our impactor were 0.78 and 0.80, respectively. Analysis of selected elements in size-segregated emission particles additionally confirmed the suitability of our system. The measurements showed that the mass size distributions were generally bimodal, with the most pronounced mass peak in the 1-2 microm size range. The first results of elemental mass size distributions showed some distinctive differences in comparison to the most common ambient anthropogenic sources (i.e., traffic emissions). For example, trace elements, like Pb, Cd, As, and V, typically related to traffic emissions, are usually more abundant in particles less than 1 microm in size, whereas in our specific case they were found at about 2 microm. Thus, these mass size distributions can be used as a signature of this source. Simultaneous measurements of size-segregated particles at the source and in the surrounding environment can therefore significantly increase the sensitivity of the contribution of a specific source to the actual ambient concentrations.     

Adsorption kinetics of platinum group elements in river water

The uptake of platinum group elements (PGE) by different preparations of estuarine sediment suspended in filtered river water has been examined. For a given PGE, adsorption time courses to untreated sediment and to sediment whose hydrous metal oxides or organic matter had been removed by appropriate chemical treatments were similar. Adsorption of Rh(lll) and Pt(IV) proceeded via a first-order reversible reaction. For Rh, forward rate constants were 1 order of magnitude greater than reverse rate constants, but for Pt, forward and reverse constants were comparable. Respective system response times, required to attain 63% of the new equilibrium, ranged from about 10 to 30 h and 2 to 20 h. In contrast, rapid, initial uptake of Pd(ll) was succeeded, in most instances, by a protracted period of desorption, requiring a more complex mechanistic interpretation. In all cases, adsorption was reduced following a period of PGE equilibration with filtered river water, suggesting that complexation with natural organic ligands exerts a significant control on the adsorption process by, for example, stabilizing PGE in solution. Exchangeability of adsorbed PGE, evaluated by ammonium acetate extraction, decreased in the order Pd > Pt > Rh, in qualitative agreement with the proposed or modeled adsorption mechanisms. Experimental results, together with independent assessments of PGE mobility from secondary sources (e.g. road dust), indicate that Pd has the greatest potential for long-range transport and bioaccumulation in the aquatic environment.     

Fingerprinting metals in urban street dust of Beijing, Shanghai, and Hong Kong

Street dust samples were taken between July and December 2005 at 25 locations in Shanghai, Beijing, and Hong Kong and sieved to 63 microm particle size before elemental analyses by CHN analyzer, XRF and ICP-MS. About 60% of the particles from the Beijing and Shanghai sieved samples were < 10 microm mean diameter, and approximately 20% were < 2 microm mean diameter, so that they are readily resuspendable and respirable with increased risk of adverse health impacts. The optical size distributions determined by electron microscopy were reasonably similar to the mass size distributions of total suspended particulate matter (TSP) at these two megacities. Hong Kong street dust particles were coarser with only about 3% of the sieved samples being < 10 microm. The elemental composition profile of Hong Kong street dust differs considerably from those of Beijing and Shanghai, being more abundant in C, S, Cr, Cu, Ce, and Zn due to higher traffic density. In particular, the vehicle contribution to Hong Kong street dust is shown by order-of-magnitude relative enhancements of Fe and Cr compared with those in TSP sampled nearby, attributed to vehicle iron and stainless-steel wear and tear and rusting contributing to street dust in the street canyons. The concentrations of Cr in Hong Kong street dust, measured from 52Cr and 53Cr by ICP-DRC-MS after a modified three-stage microwave-assisted acid digestion, are higher than those reported elsewhere.     

Implications of platinum-group element accumulation along U.S. roads from catalytic-converter attrition

Automobile catalytic converters are dispersing platinum-group elements (PGEs) Rh, Pt, and Pd into the environment (1-3). This paper represents the first detailed study to assess the PGE content of soils and grasses from U.S. roadsides. These soils were analyzed using cation exchange pretreatment and ultrasonic nebulizer-ICP-MS (4). Highway and several urban sites showed Pt abundances of 64-73 ng/g immediately adjacent to the roadside, with corresponding Pd and Rh abundances of 18-31 ng/g and 3-7 ng/g, respectively. All Pt and most Pd and Rh abundances are statistically above local background soil values. Platinum, Rd, and Rh show positive correlations with traffic-related elements (Ni, Cu, Zn, and Pb) but no correlations with nontraffic-related elements (Y, Ga). Iridium and Ru show no correlations with any of these trace elements. These PGE abundances are comparable to European studies (5-7) and are approaching concentrations that would be economically viable to recover. This study also demonstrates transport of Pt statistically above background more than 50 m from the roadside. Further study is necessary to see how mobile the PGEs are in roadside environments, but these initial data indicate only Pt is taken up by plants.     

Estimation of the contributions of brake dust, tire wear, and resuspension to nonexhaust traffic particles derived from atmospheric measurements

Size-fractionated samples of airborne particulate matter have been collected in a number of campaigns at Marylebone Road, London and simultaneously at background sites either in Regents Park or at North Kensington. Analysis of these samples has enabled size distributions of total mass and of a number of elements to be determined, and roadside increments attributable to nonexhaust emissions arising from traffic activity have been calculated. Taking a novel approach, the combined use of size distribution information and tracer elements has allowed the separate estimation of the contributions of brake dust, tire dust, and resuspension to particle mass in the range 0.9-11.5 μm aerodynamic diameter and mean contributions (± s.e.) at the Marylebone Road sampling site are estimated as resuspended dust 38.1 ± 9.7%, brake dust 55.3 ± 7.0%, and tire dust 10.7 ± 2.3%, (accounting for a total of 104.1% of coarse particle mass in the traffic increment above background).     

Persistent organic pollutants in the dusts that settled across lower Manhattan after September 11, 2001

The explosion and collapse of the World Trade Center (WTC) was a catastrophic event that produced an aerosol impacting many workers, residents, and commuters during the first few days after September 11, 2001. During the initial days that followed, 14 bulk samples of the settled dust were collected at locations surrounding the epicenter of the disaster, including one indoor location. Some samples were analyzed for many potential hazards, including inorganic and organic constituents as well as morphology. The results of the analyses for persistent organic pollutants are described herein, including polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and select organochlorine pesticides on settled dust samples. The sigma86-PCBs comprising less than 0.001% by mass of the bulk in the three bulk samples analyzed indicated that PCBs were of limited significance in the total settled dust across lower Manhattan. Likewise, organochlorine pesticides, including chlordanes, hexachlorobenzene, heptachlor, 4,4'-DDE, 2,4'-DDT, 4,4'-DDT, and Mirex, were found at low concentrations in the bulk samples. Conversely, the sigma37-PAHs comprised up to nearly 0.04% (<0.005-0.039%) by mass of the bulk settled dust in the six bulk samples. Further size segregation of these three initial bulk samples and seven additional samples indicates that sigma37-PAHs were found in higher concentrations on relatively large particles (10-53 microm), representing up to 0.04% of the total dust mass. Significant concentrations were also found on fine particles (<2.5 microm), often accounting for approximately 0.005% by mass. We estimate that approximately 100-1000 tons of sigma37-PAHs were spread over a localized area immediately after the WTC disaster on September 11.     

Airborne brake wear debris: size distributions, composition, and a comparison of dynamometer and vehicle tests

Particle size distributions of light-duty vehicle brake wear debris are reported with careful attention paid to avoid sampling biases. Electrical low-pressure impactor and micro-orifice uniform deposit impactor measurements yield consistent size distributions, and the net particulate matter mass from each method is in good agreement with gravimetric filter measurements. The mass mean diameter of wear debris from braking events representative of urban driving is 6 microm, and the number-weighted mean is 1-2 microm for three currently used classes of lining materials: low metallic, semimetallic, and non-asbestos organic (NAO). In contrast, the wear rates are very material dependent, both in number and mass of particles, with 3-4 times higher emissions observed from the low metallic linings as compared to the semimetallic and NAO linings. Wind tunnel and test track measurements demonstrate the appearance of micron size particles that correlate with braking events, with approximately 50% of the wear debris being airborne for the test vehicle in this study. Elemental analysis of the wear debris reveals a consistent presence of the elements Fe, Cu, and Ba in both dynamometer and test track samples.     

Platinum and palladium emissions from on-road vehicles in the Kaisermühlen Tunnel (Vienna, Austria)

Total and size-segregated Pt and Pd emission factors from on-road vehicles were measured in the Kaisermühlen Tunnel in Vienna, Austria. Aerosol sampling was performed simultaneously inside and outside the tunnel during April and May 2005. Analysis of the acid-digested aerosol samples was performed using a preconcentration procedure with subsequent on-line detection by electro-thermal atomic absorption spectrometry (ETAAS). Inside the tunnel distinctly increased Pt and Pd concentrations were found with highest levels in total suspended particulate matter samples and reduced concentrations in the size-segregated PM10 and PM2.5 samples. Emission factors were calculated from concentration differences between tunnel inside and tunnel outside samples, the distance between tunnel entrance and sampling location, the ventilation rate, and the number of vehicles passing through the tunnel. Emission rates observed for Pt ranged from 38 +/- 5.9 to 146 +/- 13 ng veh(-1) km(-1), whereas the emission factors of Pd varied between 13 +/- 2.1 and 42 +/- 4.1 ng veh(-1) km(-1). Variations in the emission rates were assumed to originate from alterations in traffic conditions. Size-segregated investigations revealed that the major part of Pt and Pd emissions were released in the coarse aerosol mode (size fraction > PM10), nevertheless a considerable fraction (approximately 12% and approximately 22% respectively) was emitted in the inhalable PM2.5 fraction.     

A 50-year record of platinum, iridium, and rhodium in Antarctic snow: volcanic and anthropogenic sources

Antarctic snow preserves an atmospheric archive that enables the study of global atmospheric changes and anthropogenic disturbances from the past. We report atmospheric deposition rates of platinum group elements (PGEs) in Antarctica during the last ～ 50 years based on determinations of Pt, Ir, and Rh in snow samples collected from Queen Maud Land, East Antarctica to evaluate changes in the global atmospheric budget of these noble metals. The 50-year average PGE concentrations in Antarctic snow were 17 fg g(-1) (4.7-76 fg g(-1)) for Pt, 0.12 fg g(-1) (<0.05-0.34 fg g(-1)) for Ir, and 0.71 fg g(-1) (0.12-8.8 fg g(-1)) for Rh. The concentration peaks for Pt, Ir, and Rh were observed at depths corresponding to volcanic eruption periods, indicating that PGEs can be used as a good tracer of volcanic activity in the past. A significant increase in concentrations and crustal enrichment factors for Pt and a slight enhancement in enrichment factors for Rh were observed after the 1980s. This suggests that there has been large-scale atmospheric pollution for Pt and probably for Rh since the 1980s, which may be attributed to the increasing emissions of these metals from anthropogenic sources such as automobile catalysts and metal production processes.     

Greenland snow evidence of large scale atmospheric contamination for platinum, palladium, and rhodium

Since 1976 in the United States, Canada, and Japan, and later in other countries, the exhaust system of gasoline powered cars has been equipped with catalytic converters containing Pt and/or Pd and/or Rh. This has resulted in a very significant decrease in urban air pollution for various chemical species such as NOx, CO, and hydrocarbons. There has however been concern that their ever increasing use might lead to Platinum Group Metals (PGMs) becoming widely dispersed in the environment. From the analysis of Pt, Pd, and Rh in central Greenland recent snow and ancient ice using the ultrasensitive inductively coupled plasma sector field mass spectrometry technique, we show here that the concentrations of these metals in snow dated from the mid 1990s are indeed approximately 40-120 times higher than in ice dated from 7000 years ago. The fact that such an increase is observed far away from populated areas at a high altitude location indicates there is now a large scale contamination of the troposphere of the Northern Hemisphere for PGMs. Pt/Rh mass ratio in the most recent snow samples is close to the same ratio documented for catalytic converter exhausts in a recent study, which suggests that a large fraction of the recent increase for Pt and Rh might originate from automobile catalytic converters.