Search

Abstract: Nucleation mode particles were investigated for their morphology using TEM and the presence or absence of solid cores was addressed. At cold start idle nucleation particles were observed in the exhaust of a diesel passenger car. These particles occurred with both low and high S fuel and were only partly volatile in a thermodenuder, which indicates that the composition was not sulfate and as derived from TEM/EDX (transmission electron microscopy/energy dispersive X-ray analysis) probably not ash. It could be high boiling hydrocarbons, or primary soot particles. With all fuels at warm idle no nucleation particles and only soot particles were observed in the SMPS and the TEM. With 3.0×1011 s−1 the total soot particle number during idle was much less than during driving, e.g. at 120kmh−1 the emission rate was 6.7×1012 s−1. At high load and high S fuel 10–20nm nucleation particles were observed by SMPS and TEM. A thermodenuder at 280°C and TEM showed that all nucleation particles were volatile. EDX gave a weak S-signal only. Some nucleation particles contained smaller spots (1–3nm) with a very high contrast, which might be due to heavy elements. However, under the electron beam of the TEM these spots disappeared and EDX analysis was not possible. With low S fuel at 120kmh−1 only soot particles and no nucleation particles were observed. [Copyright &y& Elsevier]

In-situ measurements of various properties of traffic-related aerosol particles have been performed with a mobile laboratory. The measured aerosol quantities include particle chemical composition (sulfate, nitrate, total organic matter, ammonium, black carbon) as well as particle size distributions covering diameters from 10 to 300nm, and total particle number density. Additionally, gas phase emissions (CO2, NO, NO2) were monitored. We performed six measurement drives in the vicinity of the city of Aachen (population ca. 260,000) at 50.8°N, 6.1°E in Germany on motorways, rural roads, and in the inner city of Aachen in June 2005. The results indicate that the main influence of traffic on the aerosol properties results in soot particles coated with organic matter, having a modal diameter around 100nm (“soot mode”). The abundance of these particles was found to be highest in the inner city traffic. Nucleation mode particles (around 30nm) have been observed occasionally during truck chasings on motorways. These particles consisted mainly of organic compounds but included possibly also a sulfuric acid core. Data observed under “motorway background” conditions were similar to the rural regional road data. Highest number concentrations have been observed during truck chasings. Comparison between non-refractory (here with respect to 600°C) and total particle volume indicated a higher contribution of refractory material under all traffic-influenced conditions compared to rural road data. Fuel specific emission ratios were derived for a subset of 18 truck-chasing experiments, yielding (8.3±5.8)×1015 kg−1 for particle number, 224±136mgkg−1 for black carbon, 125±125mgkg−1 for organic matter, 17±12gkg−1 for NO and 18±14gkg−1 for NO x (mean values and standard deviations). [Copyright &y& Elsevier]

Within the framework of the AIDA soot aerosol campaign diesel soot particles, spark generated soot particles, and aerosol mixtures were characterized with respect to their chemical state using different surface sensitive analysis methods. A comparison between diesel soot and graphite spark generated soot revealed a significant difference in the chemical composition of the particle surfaces. No distinct change from external to internal mixing could be detected by single particle mass spectrometry for mixtures of diesel soot and (NH4)2SO4 aerosol since the spectra of diesel soot and (NH4)2SO4 aerosol were surprisingly similar due to sulfate on the surface of diesel soot particles and traces of carbon impurities on ammonium sulfate particles. In addition to the expected formation of new particles a considerable change of the soot particle surface was detected while exposing diesel soot or spark generated soot to α-pinene and ozone, indicating a surface layer formed by oxidation products of α-pinene. However, the oxygen-containing hydrocarbon fragments detected by single particle mass spectrometry were distinctly different for the two soot types, which can be explained by either the different product adsorption or ionization behavior. Depositions of α-pinene reaction products on the surface could be confirmed by QMS-SIMS and XPS for particles of both types of soot. Due to the high mass resolution of TOF-SIMS acidic derivatives were identified as reaction products of α-pinene and ozone. The analytical methods applied in this work elucidated the different properties of spark generated soot compared to diesel soot. Therefore, spark generated soot should only be used with care as a general diesel soot surrogate. [Copyright &y& Elsevier]

A single-particle mass spectrometer (LAMPAS-2) was operated at an Autobahn (high-speed highway with significant heavy-duty diesel traffic), an urban and a rural site in the vicinity of Aachen (Germany). The single-particle mass spectra could be classified into eight classes, representing different types of mineral particles, inorganic salt particles, and carbonaceous aerosol particles. At all three sites characteristic patterns of diesel exhaust particles with and without secondary compounds (ammonium sulfate/nitrate) were observed. The relative contribution of diesel soot to the number of 0.5 μm particles was 23% or 35% at the rural and the Autobahn site, respectively. The absolute number of diesel exhaust particles was three times larger at the Autobahn site. At the urban site the diesel exhaust particle contribution ranged from 10% to 35%, depending on the local operation of heavy-duty construction vehicles. Elemental carbon and carbonaceous particles made up the majority number of the 0.5 μm particles, and showed a decreasing percentage towards 2 μm particle size. As expected mineral-soil-derived particles showed the reverse size distribution. The data sets were also analyzed using a reference pattern obtained from exhaust particles of a light-duty diesel vehicle as a fingerprint. A similar trend of the contribution to the diesel-exhaust-like particle class was found, although the absolute numbers were somewhat different. On-line single-particle mass spectrometry proved to be a promising tool to identify individual particles if characteristic reference spectra were available. [Copyright &y& Elsevier]