Metal particle seeding on urban surface samples.

In order to estimate the resuspension of the particles empirically, it is necessary to carry out a homogeneous distribution of the particles on the tested surfaces. Thus, in many studies, seeding or deposition in experimental chambers is performed to quantify initial concentrations for subsequent resuspension experiments. The current study was carried out to assess metal particle seeding efficiency on four types of urban surfaces (slate, facade coating, tile, and glass) in a test chamber. To achieve this objective, we compared firstly different solubilization techniques of silver polydisperse particles (1.3-3.2 µm and 0.5-1.0 µm) and gold polydisperse particles (Ø˂5 µm) for chemical quantification by ICP-MS. The result showed better yields in the case of gold for all solubilization techniques studied (82% ± 5% to 98% ± 2% for gold versus 23% ± 18% to 84% ± 12% for silver). Based on this result, four seeding tests were carried out with the gold particles (distribution in chamber centered on 1µm). The concentrations seeded on urban surfaces (mean ± SD) varied from 10,900 ± 1,900 µg.m-2 (facade coating sample) to 1900 ± 390 µg.m-2 (glass sample). The relative standard deviation of the measured concentrations equaled 9.5% (tested for aluminum foils), which was less than the measurement uncertainty of the recording equipment (≈14%) and reflected good seeding homogeneity. Observations by scanning electron microscopy coupled to microanalysis (SEM-EDX) were in agreement with these conclusions.

Platinum group elements in atmospheric PM10 particles and dry deposition in France.

Platinum group elements (PGEs, i.e. platinum, Pt; palladium, Pd; and rhodium, Rh) catalyse over 90% of carbon monoxide, nitrogen oxides and hydrocarbons from combustion residues into water vapour, carbon dioxide and nitrogen in the vehicle's catalytic converter. But there is a major concern over these metals in the scientific world, since they are emitted by catalytic converters and accumulating in the environment. The distribution of PGEs in PM10 fraction was studied in an open urban site (Nantes, France) and in a tunnel (Paris, France) using low- and high-volume air samplers. PGEs were also investigated in dry deposition particles and deposited dust sampled in the tunnel. Pd occurred at the highest levels in both PM10 and dry deposition samples, followed by Rh and Pt. Maximum concentrations in PM10 fraction were 114 pg m-3 for Pd, 14.3 pg m-3 for Rh and 3.3 pg m-3 for Pt in the urban site (Nantes) and 91 pg m-3 for Pd and 16 pg m-3 for Rh in the tunnel (Paris). The concentrations for dry depositions in the tunnel were 261 µg kg-1 for Pt, 431 µg kg-1 for Pd and 85 µg kg-1 for Rh. The results on PGEs levels in atmospheric particles and dry depositions are the first data of their kind in France and will provide new insights into the contribution of catalytic converters to the environment. We also observed Pd and Rh being 2 times higher PM10 particles compared to dry depositions, leading us to suggest that particles rich in Pd and Rh are smaller than 10 µm. An overall concentration trend of Pd > Rh > Pt was observed in all samples, showing the replacement of Pt by Pd and Rh in newer catalytic converters.

Platinum group elements study in automobile catalysts and exhaust gas samples.

Platinum-Group Elements (PGEs, i.e. platinum; Pt, palladium; Pd and rhodium; Rh) are extensively employed in the production of automotive catalytic converters to catalyze and control harmful emissions from exhaust fumes. But catalytic converters wear out over time and the emission of PGEs along with the exhaust fumes are nowadays known to be the main reason of the presence of PGEs in urban environments. PGEs contents were studied on three gasoline 3-way catalytic convertors with low, medium and high kilometers. PGEs emission factors via exhaust gases from Euro 3, 4, 5 and 6 gasoline and diesel vehicles, were monitored using catalytic converters. Results show variable content for PGEs for the three converters, in the ranges of 6-511, 0.5-2507 and 0.1-312 mg kg-1 for Pt, Pd and Rh respectively. PGEs contents in different catalyst supports show the replacement of Pt by Pd in more recent converters. Analysis of the exhaust gas shows that catalytic converters expel up to 36.5 ±â€¯3.8 ng km-1 of Pt, 8.9 ±â€¯1.1 ng km-1 of Pd and 14.1 ±â€¯1.5 ng km-1 of Rh. Higher emissions of PGEs have been observed by gasoline Euro 3 vehicle, possibly due to the older technology of motorization and of the catalytic converter in this vehicle. Euro 3 and 4 diesel vehicles seem to emit more PGEs during urban cycles. Emission of PGEs has been also observed during the cold start of the majority of vehicles which seems to be the result of incomplete combustion during the rise of temperature in the engine. Higher PGEs emissions were also observed during motorway cycles in newer (Euro 4 and 5) petrol and diesel vehicles, conceivably due to the greater combustion as the engine speeds up during this cycle.

Evaluation of the reaction artifacts in an annular denuder-based sampler resulting from the heterogeneous ozonolysis of naphthalene.

The heterogeneous ozonolysis of naphthalene adsorbed on XAD-4 resin was studied using an annular denuder technique. The experiments involved depositing a known quantity of naphthalene on the XAD-4 resin and then measuring the quantity of the solid naphthalene that reacted away under a constant flow of gaseous ozone (0.064 to 4.9 ppm) for a defined amount of time. All experiments were performed at room temperature (26 to 30 °C) and atmospheric pressure. The kinetic rate coefficient for the ozonolysis reaction of naphthalene adsorbed on XAD-4 resin is reported to be (10.1 ± 0.4) × 10(-19) cm(3) molecule(-1) s(-1) (error is 2σ, precision only). This value is five times greater than the currently recommended literature value for the homogeneous gas phase reaction of naphthalene with ozone. The obtained rate coefficient is used to evaluate reaction artifacts from field concentration measurements of naphthalene, acenaphthene, and phenanthrene. The observed uncertainties associated with field concentration measurements of naphthalene, acenaphthene, and phenanthrene are reported to be much higher than the uncertainties associated with the artifact reactions. Consequently, ozone reaction artifact appears to be negligible compared to the observed field measurement uncertainty results.