Analytical Methods

• Gas chromatographic analysis of trace gas samples in stainless steel canisters (Restek "Silcosteel")

  • Organic trace gas content in gas samples (in ambient air and tail pipe exhaust)
  • Analysis of breath samples for medical purposes
• Signature analysis for the determination of the Diesel soot contribution to particulate matter
• Determination of organic carbon, elemental carbon (soot) and mineral components in by heating-up particulate matter and using sensitive cavity ringdown-based CO₂- and H₂O-detection techniques
• Operation of Tunable Diode Laser Absorption Spectrometers (TDLAS) as  reference method of trace gas analysis and for the direct detection of trace gases in the ppt-range

Signature analysis for the determination of Diesel soot contribution to particulate matter

A novel method for the identification and quantification of Diesel soot to total particulate matter  [1, 2] was developed. This is a method in which a particulate sample is baked on a quartz filter in a closed system and is then analyzed by gas chromatography. Exclusively organic fractions of particulate matter are captured.

Emission tests on different diesel vehicles of various model year and type showed a typical, reproducible signature which allows an identification of the Diesel soot contribution. The signature can be distinguished unambiguously from that of other  sources of particulate matter (such as domestic fuel, tire wear, etc.)  Based on these measurements, a proportionality between collected mass of Diesel soot and the signature strength of the characteristic peaks is observed. Using the signature mass-relation the Diesel soot contribution in any ambient air sample can be calculated (see details in Figure 2).

Studies on the speciation of particulate matter and of NO₂ in an urban environment using a mobile measuring laboratory (MOBILAB)

Until recent years it was assumed that anthropogenic nitrogen release of NO and NO₂ (in particular that from traffic) take place almost exclusively in the form of nitric oxide (NO). For some time European metropolitan areas show an opposite trend in the time series of NO and NO₂: while NO is decreasing continuously over the years in parallel with the introduction of the 3-way catalytic converters, the measured concentrations of NO₂ remain almost constant. Two different reasons are responsible for the stagnation of the urban NO₂ concentrations:

a)  The titration of NO by background ozone generating equivalent amounts of NO₂.

b) The growing proportion of direct NO₂ emissions from diesel vehicles with oxidation catalysts.

In the atmosphere, there is a rapid reaction of NO with ozone, which is responsible for the fact that under traffic-dominated conditions ozone background levels (O₃-BG, which can be measured at the lee-site of a city) can be consumed completely forming equivalent amounts of NO₂. Thus, under these conditions, background ozone mixing ratios control the prevailing inner city mixing ratio of NO₂. Therefore, regardless of the amount of NO mixing ratios in the inner cities a nearly constant NO₂ mixing ratio is measured (see Fig. 3). Therefore, declining NO₂ mixing ratios for inner city districts could be expected only if NO mixing ratios are reduced below background ozone. It is worth noting that under "n_NO > n_O3-BG" conditions (O_3-BG ≈ 60 µg/m³) the resulting NO₂ mixing ratios are well above the limit of the NO₂ annual mean of 40 µg/m³.

Figure 4 shows the result of a dynamometer test  of a modern diesel vehicle equipped with an oxidation catalyst, in which the vehicle emits significantly more NO₂ as NO. Unlike gasoline vehicles with three-way catalysts in the exhaust of a diesel vehicle only the hydrocarbons and CO, but not the contained nitrogen oxides are reduced. In fact, due to thermodynamic reasons depending on the temperature the oxidation catalyst converts part of the originally produced NO to NO₂. The emissions of diesel vehicles are currently the largest source of nitrogen oxides from road transport. Recent measurements [5] in a road tunnel in Düsseldorf delivered NO/NO₂-fractions of 65% / 35%. In an ongoing PhD-thesis a comparative assessment of the importance of both NO₂ source strengths for inner-city areas is undertaken.

Literature

[1] Janson, S., H.-J. Buers, D. Klemp, F. Rohrer (2008): „Methode zur Quantifizierung des Dieselrußanteils im Feinstaub“, VDI-Berichte (Band 2040): Neue Entwicklungen bei der Messung und Beurteilung der Luftqualität, 101 – 109.

[2] Buers Hermann-Josef, Klemp Dieter, Mueller Klaus-Peter, Rohrer Franz: Method for fine dust analysis. Forschungszentrum Juelich, July 2008: EP1938082.

[3] Lufthygienische Jahresberichte des Bayerischen Landesamtes für Umweltschutz, 1990 – 2008.

[4] Klemp, D., D. Mihelcic, B. Mittermaier (2012): Messung und Bewertung von Verkehrsemissionen“, ISBN: 978-3-89336-546-3, pp. 318.

[5] Urban, S., „Charakterisierung der Quellverteilungen von Feinstaub und Stickoxiden in ruralem und urbanem Gebiet“, PhD thesis, Universität Wuppertal, Juni 2010, pp. 211.