Ralf Kurtenbach

Nonintrusive optical measurements of aircraft engine exhaust emissions and comparison with standard intrusive techniques

Nonintrusive systems for the measurement on test rigs of aeroengine exhaust emissions required for engine certification (CO, NO(x), total unburned hydrocarbon, and smoke), together with CO(2) and temperature have been developed. These results have been compared with current certified intrusive measurements on an engine test. A spectroscopic database and data-analysis software has been developed to enable Fourier-transform Infrared measurement of concentrations of molecular species. CO(2), CO, and NO data showed agreement with intrusive techniques of approximately ?30%. A narrow-band spectroscopic device was used to measure CO(2) (with deviations of less than ?10% from the intrusive measurement), whereas laser-induced incandescence was used to measure particles. Future improvements to allow for the commercial use of the nonintrusive systems have been identified and the methods are applicable to any measurement of combustion emissions.

Nitrous Oxide (N2O) Emissions from Vehicles

N2O is an important greenhouse gas and accurate emission data are required to assess its impact on global climate. It is well established that automobiles, particularly those equipped with 3-way catalysts, emit N2O. However, the vehicle contribution to the global N2O budget is uncertain. We report results of N2O emission measurements performed in a road tunnel in Germany and using a chassis dynamometer system in the USA. We estimate that the global vehicle fleet emits (0.12±0.06) Tg yr−1 of N2O. From the emission factor (g N2O/g CO2) determined an annual N2O emission of (0.12±0.06) Tg yr−1 of N2O (0.08±0.04 Tg N yr−1) for the global vehicle fleet has been estimated which represents 1–4% of the atmospheric growth rate of this species.

Mechanistic study of the heterogeneous conversion of NO2 into HONO and N2O on acid surfaces

The heterogeneous conversion of NO2 into HONO and N2O on acid surfaces has been investigated in an 11 l Pyrex glass reactor under simulated atmospheric conditions and in a 64 l quartz glass reactor at reduced pressure. NO2, N2O and HONO were monitored with time by long-path tunable IR diode laser absorption spectroscopy using single vibrational rotational lines at 1641.0, 1254.47 and 1254.46 cm–1, respectively.The experimental results show that NO2 is heterogeneously converted on acid surfaces into HONO and then into N2O. HONO formation in the reaction system has been found to occur by the heterogeneous reaction of NO2 with adsorbed water on the surface and does not require NO. The experimental findings indicate that the nitrosyl ion probably plays an important role in converting HONO into N2O and HNO3. A mechanism is proposed which can explain the experimental findings.

Primary NO2 emissions and their impact on air quality in traffic environments in Germany

BackgroundThe decreasing NOX concentrations at urban measurement stations in Germany are in agreement with the reduction of NOX emissions from vehicular traffic. However, the measured NO2 concentrations are stagnating nationwide. In 2010, at more than the half of the urban measurement stations in Germany, annual mean values for NO2 exceeded the new Europe-wide limit value of 40 μg/m3 (20 ppbv) NO2. Similar findings are reported from many other member states of the European Union.ResultsThe observed trend of the airborne NO2 concentrations has different reasons. Firstly, the NO2/NOx emission ratio has increased significantly during the last two decades. Furthermore, secondary NO2, caused by the titration reactions of NO with ozone (O3) and peroxy radicals (RO2), is responsible for the major fraction (approximately 70%) of the measured NO2. However, secondary NO2 shows a highly nonlinear dependency on NOx and thus, is decreasing much more slowly than expected from the decreasing NOx levels. Based on the results from the present study, the increased NO2/NOX emission ratio can only explain a minor fraction of the observed high airborne NO2 concentration in the city center.ConclusionsA further reduction of primary NO2 emissions, due to improved exhaust gas treatment, will not have a strong influence on urban NO2 levels, and a further significant reduction of the NOX emissions, in particular from vehicular traffic, is necessary in order to meet the annual mean limit value for NO2 of about 20 ppb in the future.

Construction of a photocatalytic de-polluting field site in the Leopold II tunnel in Brussels

Within the framework of the European Life+-funded project PhotoPAQ (Demonstration of Photocatalytic remediation Processes on Air Quality), which was aimed at demonstrating the effectiveness of photocatalytic coating materials on a realistic scale, a photocatalytic de-polluting field site was set up in the Leopold II tunnel in Brussels, Belgium. For that purpose, photocatalytic cementitious materials were applied on the side walls and ceiling of selected test sections inside a one-way tunnel tube. This article presents the configuration of the test sections used and the preparation and implementation of the measuring campaigns inside the Leopold II tunnel. While emphasizing on how to implement measuring campaigns under such conditions, difficulties encountered during these extensive field campaigns are presented and discussed. This included the severe de-activation observed for the investigated material under the polluted tunnel conditions, which was revealed by additional laboratory experiments on photocatalytic samples that were exposed to tunnel air. Finally, recommendations for future applications of photocatalytic building materials inside tunnels are given.

Carbon monoxide and carbon dioxide concentrations in Santiago de Chile associated with traffic emissions

CO/CO2 ratios have been measured in different locations of Santiago de Chile city. Measurements were carried out in a tunnel (prevailing emissions from cars with catalytic converter) and close to heavy traffic streets. Concentrations measured along the city traffic tunnel or temporal profiles of concentrations measured near heavy traffic streets allow an estimation of CO/CO2 ratios emitted from mobile sources. Values obtained range from 0.0045 ± 0.0006 to 0.0100 ± 0.0004 and depend on the prevailing type of mobile sources. In particular, lowest values were found close to a street with heavy traffic dominated by diesel-powered public transportation, while the highest values were found at the city tunnel. Places located near streets of mixed mobile sources (public buses and cars) showed intermediate values. Average CO/CO2 ratios are compatible with emission factors proposed for Santiago’s main mobile sources.

Athens airport air quality study by remote sensing with DOAS, FTIR and ceilometer

The impact of air traffic on the atmosphere was subject to several works in the last years. But little scientific work has been done concerning airport air quality. Airports themselves often measure concentrations of the main pollutants and use dispersion models to asses the air quality situation. Emission inventories of airport are not well known generally because a lot of different emission sources exist. A database is required to characterise real-world emission source strengths as well as air quality and meteorological data at airports that will serve as an input and as validation data for modelling work. Dedicated studies were performed to follow these objectives. To develop a database of air quality and meteorological data a measurement campaign was carried out at the Athens International Airport (AIA). The campaign from 13 until 25 September 2007 was realised with the application of in situ (two mast equipped with fast (sonic anemometers) and slow sensors at various heights) and remote sensing techniques as DOAS, FTIR, SODAR with RASS and ceilometer as well as the aid of existing equipment available by the participant partners that was transferred to the AIA, allowing the sharing of knowledge and infrastructure. The concept of this measurement campaign will be presented. Some results of interpretation of measured data will be discussed as aircraft emission indices during take-off, influence of aircraft emissions upon airport air quality, estimation of the airport emission source strengths and influence of airport emissions upon air quality in the surroundings.

NO2 Measurement Techniques: Pitfalls and New Developments

Reliable measurements of atmospheric trace gases are necessary for both, a better understanding of the chemical processes occurring in the atmosphere, and for the validation of model predictions. Nitrogen dioxide (NO2) is a toxic gas and is thus a regulated air pollutant. Besides, it is of major importance for the oxidation capacity of the atmosphere and plays a pivotal role in the formation of ozone and acid precipitation. Detection of NO2 is a difficult task since many of the different commercial techniques used are affected by interferences. The chemiluminescence instruments that are used for indirect NO2 detection in monitoring networks and smog chambers use either molybdenum or photolytic converters and are affected by either positive (NOy) or negative interferences (radical formation in the photolytic converter). Erroneous conclusions on NO2 can be drawn if these interferences are not taken into consideration. In the present study, NO2 measurements in the urban atmosphere, in a road traffic tunnel and in a smog-chamber using different commercial techniques, i.e. chemiluminescence instruments with molybdenum or photolytic converters, a luminol based instrument and a new NO2-LOPAP, were compared with spectroscopic techniques, i.e. DOAS and FTIR. Interferences of the different instruments observed during atmospheric measurements were partly characterised in more detail in the smog chamber experiments. Whereas all the commercial instruments showed strong interferences, excellent agreement was obtained between a new NO2-LOPAP instrument and the FTIR technique for the measurements performed in the smog chamber.

Determination of VOCs in traffic exhaust by FTIR absorption spectrometry

Infrared spectral features of organic hydrocarbons were investigated with respect to single compounds. A separation and consequently a quantitative concentration determination is possible for ethane, ethene, ethyne, propene, iso-butene, benzene, toluene, o-xylene, m-xylene and p-xylene using a MCT detector with a cut-off frequency below 660 cm-1. The spectral features of propane, butane, pentane and hexane cannot be separated. In order to be able to derive parameters, such as detection limits, accuracy, precision and the influence of interfering species or different reference data, validation measurements were carried out in a road tunnel and in the laboratory using an open White mirror compartment and closed White cells. FTIR spectra were collected with two spectrometers at different spectral resolutions. Parallel GC measurements were made for comparison.

Issues related to aircraft take-off plumes in a mesoscale photochemical model

The physical and chemical characteristics of aircraft plumes at the take-off phase are simulated with the mesoscale CAMx model using the individual plume segment approach, in a highly resolved domain, covering the Athens International Airport. Emission indices during take-off measured at the Athens International Airport are incorporated. Model predictions are compared with in situ point and path-averaged observations (NO, NO₂) downwind of the runway at the ground. The influence of modeling process, dispersion properties and background air composition on the chemical evolution of the aircraft plumes is examined. It is proven that the mixing properties mainly determine the plume dispersion. The initial plume properties become significant for the selection of the appropriate vertical resolution. Besides these factors, the background NOx and O₃ concentration levels control NOx distribution and their conversion to nitrogen reservoir species.