The emission indices of aircraft engine exhausts were measured at airports non-intrusively by FTIR emission spectrometry at the engine nozzle exit as well as by FTIR absorption spectrometry and DOAS (Differential Optical Absorption Spectrometry) behind the aircraft.
Two measurement campaigns were performed to compare these different measurement methods. A kerosene powered burner was operated in that way that the different methods were applied for the exhaust gas investigations during the same time and at nearly the same exhaust gas volume. The burner was built with a nozzle exit diameter of 37 cm and a power of about 150 kW. Fresh air was pumped into the burner tube by a fan. Calibration gases as pure CO and NO were added in different amounts to vary the concentration of these gases in the exhaust. The sampling probe of an intrusive measurement system was installed in the centre of the exhaust stream near the exhaust exit for measurements of these gases and CO2 as well as NO2, UHC, SO2 and O2. An APU (GTCP36-300) in a test bed was used in the same way. CO was mixed into the exhausts near the nozzle exit. The passive FTIR instrument was operated in the test bed using special noise and vibration isolation. The open-path instruments were installed at the chimney exit on the roof of the test bed building. The deviations between the different measurement methods were in the order of ±10 up to ±20 %.
The main engines exhaust of two Boeing 767-3ZR(ER) powered by Pratt & Whitney 4060 has been intensively studied using spectroscopic methods like Fourier Transform Infrared Spectroscopy (FTIR) and Differential Optical Absorption Spectroscopy (DOAS). All cockpit data was provided by the operating airline while the thrust level was varied between idle (25% N1) and 70 % N1 where N1 is the maximum number of revolutions of the fan. The investigated gaseous species were carbon dioxide, carbon monoxide, nitrogen oxides (NO and NO2) and some hydrocarbons (C2H4, C2H2, HCOH and unburned kerosene). A comparison to the database of the International Civil Aviation Organization (ICAO) showed much higher emissions of CO and NOx-emissions in the same range. Although these two aircraft were of the same age and maintained by the same operator the emissions differed by a factor of two. Formaldehyde proved to be the most abundant hydrocarbon besides ethane and ethane.
The emission indices of aircraft engine exhausts to calculate precisely the emissions inventories of airports are not available up to now from measurements taken under operating conditions. To determine these data no installations nearby or behind the aircraft are possible at airports. That's why measurements by FTIR emission spectrometry were performed by the IMK-IFU with a spectrometer installed in a van and with total measurement time at one thrust level of about 1 minute to determine CO, NO and CO2. The FTIR instrument telescope was aligned to the engine nozzle exit of standing aircraft. A DOAS and a FTIR spectrometer with globar were used for simultaneous open-path measurements of NO, NO2, CO, CO2 and speciated hydrocarbons behind the aircraft by the TUG-VKMB. Measurement results at the airports Frankfurt/Main, London-Heathrow and Vienna are presented. The methods are evaluated by comparing CO emission indices from passive measurements with open-path data. The measured emission indices of CO show slightly higher values than the International Civil Aviation Organisation data sheets but less values for NOx emissions. A fruitful co-operation with the airlines AUA, BA and DLH as well as the airport authorities in Vienna and London-Heathrow supported this work which is financed from EC.
12 The detection of benzene and other organic compounds in vehicle exhaust by FT-IR-spectroscopy is seriously limited by the strong interference of carbon dioxide and the rather weak absorption coefficient of the gases. Therefore, a measurement device was developed which separates the components of interest (mostly VOCs) from carbon dioxide, water and nitric oxide. In addition the VOCs have to be pre- concentrated. To avoid condensation of VOCs the measurements have to take place at higher temperatures. The vehicle exhaust was led through an activated charcoal tube where the organic compounds were adsorbed. Afterwards, the charcoal tube was heated in a furnace, the VOCs were desorbed thermically and were carried by (heated) nitrogen into a gas cell with a path-length of 10 m where the concentration of the different species was measured. With the help of this measurement device a lot of VOC- components like benzene, toluene, and xylene were detected successfully. Measurements were performed on an engine test bed and a chassis dynamometer for heavy duty vehicles. The detection limit of most of the VOCs was about 2 to 3 ppb for a sampling time of 20 min. Calibration measurements showed an accuracy of 15%.
12 The emission behavior of road vehicles is usually estimated by application of emission factors and models. The validity of such factors or models in real world situations can be investigated by tunnel measurements, because road tunnels can be considered as big laboratories with well known boundary conditions. Tunnel experiments were carried out in the 10 km long Plabutschtunnel near Graz, Austria for a period of six weeks in November 1998 and another four weeks in May 1999. A UV- DOAS-system was operated in open-path mode located some 4 km inside the tunnel with pathlengths of 220 m to 430 m. To have an idea about the uniformity of the pollutant air mixture within the path, a comparison of NO2 measurements performed with a standard chemiluminescent analyser (point measurement) and the DOAS system (open-path measurement) was done. Therefore a standard air quality monitoring-system (AQM) in a container was installed in a niche inside the tunnel on one end of the DOAS path. The analysis of data showed good agreement of emissions derived from the measurements with the existing PC and HDV emission factors for CO. This was not the case for benzene and NOx emissions obtained from heavy duty vehicles.
The quantification of benzene in FTIR spectra is restricted by the interference of benzene with carbon dioxide. In this paper different methods are presented to overcome these problems with a detector of medium resolution of 0.5 cm-1. The experiments were performed either in a 10 m gas cell or as open path experiments. One method compares the peak at 673.76 cm-1 with the strongest absorption band of benzene in the single beam spectrum to the neighboring peaks, one method analyzes the shape of the peak at 674 cm-1. Another method works with an artificial background and the latest methods analyze the absorbance spectrum and serve as a reference. The results from all these methods agreed very well down to the level of 30 to 50 ppb.