Fraunhofer-Institut für Atmosphärische Umweltforschung IFU

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  • Publication
    Aircraft measurements and model simulations of the air quality in Athens, Greece
    ( 1998)
    Svensson, G.
    ;
    Klemm, O.
    Simulations with a three-dimensional time-dependent coupled photochemical and meteorological model are compared with aircraft measurements. The aircraft measurements were taken during the experimental phase of Mediterranean Campaign of Photochemical Tracers - Transport and Chemical Evolution (MEDCAPHOT-TRACE) which took place in Athens, Greece, in August-September 1994. Two days with very different circulations are presented. The first case, 12 September, is a day with rather strong synoptic forcing and the Athens Basin is well ventilated by northerly winds. The emissions from Athens are found as polluted air south of the city, over the sea. The second case is 15 September, a day when the synoptic forcing was weak and several sea-breeze systems developed in the area. Two aircraft missions were performed on this day, one at daybreak and the other in the early afternoon. Low internal boundary-layer heights caused high pollution concentrations in and over the city of Athens. Model output is extracted with the space and time information from the aircraft, i.e. a virtual flight is performed in the model. Model results and the experimental observations are compared; the general conclusion is that the model performed well on the two simulated days. The flow is complex on 15 September and both the model simulation and the observations show increasing concentration of ozone and other pollutants towards north in the basin. In the gap between two mountains in the north, there is an opposing wind that halts the sea-breeze. This creates a convergence zone which in turn causes vertical motions that transport polluted air up to above 2000 m, i.e. in this case to the free troposphere.
  • Publication
    Ozone episodes in Athens, Greece. A modelling approach using data from the medcaphot-trace
    ( 1998)
    Ziomas, I.C.
    ;
    Tzoumaka, P.
    ;
    Balis, D.
    ;
    Melas, D.
    ;
    Zerefos, C.S.
    ;
    Klemm, O.
    Making use of the extended database of air pollution and meteorological measurements, which was created within the framework of the MEDCAPHOT-TRACE project, the performance of the Urban Airshed Model was evaluated for the Greater Athens Area (GAA). This model was also used to examine the effect on ozone of 36 scenarios of possible VOC and NOx reductions of entire area-wide emission. Although the GAA is characterised by complex topography and meteorological conditions as well as inhomogenious emission characteristics, the UAM predictions compare favourably with the existing observations. The EPA proposed statistical measures are met by the model, although there is a degree of uncertainty concerning the emission inventory (within a factor of 1.5-2). It is shown that ozone abatement strategy should focus mostly on VOC emissions controls rather than controlling NOx. The VOC reduction should be of the order of 30-40 per cent in order to effectively reduce the ozone levels at the northern pa rt of the GAA, down to the European Union's limit of 90 ppb. This goal is not expected to be achieved before the year 2005.
  • Publication
    Dilution of aircraft exhaust plumes at cruise altitudes
    ( 1998)
    Schumann, U.
    ;
    Schlager, H.
    ;
    Arnold, F.
    ;
    Baumann, R.
    ;
    Haschberger, P.
    ;
    Klemm, O.
    The dilution of jet engine exhaust in the plume behind cruising aircraft is determined from measured plume properties. The data set includes in situ measurements of CO2, NO, NOy, SO2, H2O1 temperature, and contrail diameters behind subsonic and supersonic aircraft in the upper troposphere and lower stratosphere, for plume ages of seconds to hours. The set of data is extended into the range of milliseconds based on computations and measured temperature values. The bulk plume dilution is expressed in terms of the dilution ratio N which is the mass of air with which the exhaust from a unit mass of burned fuel mixes. For: 0.006 s < t < 10 (exp 4) s, the bulk dilution ratio measured in more than 70 plume encounters follows approximately N = 7000 (t/t0) 0.8, t0 = 1 s.
  • Publication
    A summer air-pollution study in Athens, Greece
    ( 1998)
    Klemm, O.
    ;
    Ziomas, I.C.
    ;
    Balis, D.
    ;
    Suppan, P.
    ;
    Slemr, J.
    ;
    Romero, R.
    ;
    Vyras, L.G.
    During a photochemical episode in September 1994, we studied transport and distribution of primary and secondary air pollutants in Athens, Greece, using a research aircraft instrumented for meteorological and air chemistry measurements, and ground-based air-pollution-monitoring stations. We performed a total of 9 flights on 7 days under various meteorological conditions and pollution levels. We report typical pollutant mixing ratios for the background boundary layer. Sea breezes of various intensities were observed during all our noon flights. The sea breezes carried air pollution of apparently different origin and photochemical age, as indicated by the O3/NOy ratios. The pollution levels within the sea breezes were, however, low compared to those in the city of Athens. Under favorable meteorological conditions, the sea breeze could penetrate the entire Athens basin, resulting in an upward flow at the foothills of Parnitha and Pendeli Mts., and filling the lower troposphere with high l evels of air pollution at altitudes of up to 2000 m and more. From these layers of high photochemical activity (O3 levels up to 200 ppb), air pollution may have been incorporated into long-range transport.
  • Publication
    Airborne, continous measurement of carbon monoxide in the lower troposphere
    ( 1996)
    Klemm, O.
    ;
    Hahn, M.K.
    ;
    Giehl, H.
    Continuous measurements of CO on-board a fast moving research aircraft in the lower troposphere were made using a system operating on the principle of reduction of HgO and subsequent detection of Hg vapor by flameless atomic absorption (AA). The AA detector is a commercial unit with a modified HgO reaction bed. The system is operated at constant pressure to stabilize reaction conditions, system response, and background signal. The key analytical parameters are as follows: detection limit 4 ppb, precision +/- 2.4 ppb, and 90 per cent response time 110 s. The system was successfully deployed in a large number of research flights over central Europe. The response time is long compared to some other instruments (such as the NOy analyzer). However, the CO measurements can be interpreted in terms of differences between the lower free troposphere (LFT) and planetary boundary layer (PBL), in terms of quantitative analyses of vertical profiles within the PBL, and with respect to relative enhanc ement ratios of primary pollutants in plumes. During our 1992 and 1993 research flights, we found CO mixing ratios between 90 and 160 ppb to be typical for the LFT over Germany. Within the PBL, typical mixing ratios were between 150 and 320 ppb, by factors between 1.3 and 3 higher than those in the LFT. Higher mixing ratios were found over or downwind of urban agglomerations, where area sources, mainly traffic, lead to peak mixing ratios of several hundred ppb up to altitudes of about 150 m above ground.
  • Publication
    Boundary-layer structure and photochemical pollution in the Harz Mountains
    ( 1996)
    Beyrich, F.
    ;
    Acker, K.
    ;
    Kalaß, D.
    ;
    Klemm, O.
    ;
    Möller, D.
    ;
    Schaller, E.
    ;
    Werhahn, J.
    ;
    Weisensee, U.
    Results from a field campaign that has been performed in summer 1993 to study photochemical pollution in the Harz Mountains, Germany, are presented. During a five-day, fair-weather period, a steady increase of the daily maximum ozone concentration up to values around 100 ppb was observed in the Harz region. The results of ozone measurements at two surface stations (404 m a.s.l. and 1142 m a.s.l., respectively) are discussed with respect to both the transport and dispersion conditions during the period and the local structure of the atmospheric boundary layer. Remarkable similarities in the time series of the ozone mixing ratio at the two places have been found which indicate some kind of quasi-homogeneity even over complex terrain. The trace gas concentrations at the top of Mt. Brocken, the highest summit of the Harz Mountains, are shown to be strongly influenced by vertical transports due to convection (at daytime) and subsidence of inversion layers (at nighttime).
  • Publication
    NATO/CCMS pilot study workshop on air pollution transport and diffusion over coastal urban areas
    ( 1995)
    Melas, D.
    ;
    Kambezidis, H.D.
    ;
    Walmsley, J.L.
    ;
    Moussiopoulos, N.
    ;
    Bornstein, R.D.
    ;
    Klemm, O.
    ;
    Asimakopoulos, D.N.
    ;
    Schiermeier, F.A.
    The NATO/CCMS Pilot Study "Air pollution transport and diffusion over coastal urban areas" held an international workshop in Athens, 3-5 May 1993. The objective of this workshop was to develop guidelines for a reference experiment in a coastal urban area. It was intended that the guidelines would be sufficiently general that they could be applied to any coastal urban area, but Athens was borne in mind as a suitable candidate location. On the first day of the workshop, invited speakers delivered their lectures on different issues of dispersion in urban coastal areas. The second day was devoted to discussions in working groups focusing on key issues, such as, emissions' inventory, meteorological measurements, surface pollutant concentration measurements, aircraft measurements, remote sensing and model evaluation. On the final half-day the rapporteur from each working group reported on its work. Their reports are briefly summarized in the present paper.
  • Publication
    Aircraft measurement of pollutant fluxes across the borders of Eastern Germany
    ( 1994)
    Klemm, O.
    ;
    Schaller, E.
    We performed a research flight along the western and eastern border of eastern Germany to estimate the transboundary flux of pollution gases during a synoptic weather situation with westerly to southwesterly winds. A dolphin flight pattern was applied to sample the boundary layer as representatively as possible while screening the vertical structure of the lower troposphere. Transboundary flux intensities were calculated using concentrations and wind vectors as measured by the aircraft. A detailed error analysis was performed to estimate two types of uncertainties in the transboundary flux measurement. The error originating from inaccuracies in meteorological and chemical measurements was estimated to be in the range 15-35 per cent (one standard deviation). The error originating from the unrepresentativeness of the data collected on the flight path is estimated to be smaller by factors between 2 and 3. Transboundary fluxes at the eastern side of eastern Germany were different from thos e at the western side at a high level of confidence (> 95 per cent). Transboundary fluxes were greater on the eastern side by a factor of 12 for SO2 and by a factor of 2.9 for NO(y). For SO2, the transboundary fluxes in the Ekman layer (EL) and inversion layer (IL) were greater than those of lower free troposphere (LET) on both sides, whereas for NO(y) and O3 higher LFT wind speeds compensated higher EL and IL mixing ratios. A compilation of all available data on pollutant gas export from eastern Germany reveals a very heterogeneous data set. Computed average fluxes, however, show good agreement with estimates of pollutant gas emissions from eastern Germany, based on energy consumption.
  • Publication
    Fog chemistry at the New England coast. Influence of air mass history
    ( 1994)
    Klemm, O.
    ;
    Bachmeier, A.S.
    ;
    Talbot, R.W.
    ;
    Klemm, K.I.
    During the spring, summer and fall seasons of 1990, we sampled fog at a coastal location in New England for chemical analysis. For the 6 sampled events, 72 h back trajectories were calculated for the associated air masses. We found that air masses leading to the sampled fog events reached our site from south/southwesterly to southeasterly directions. The chemical composition of the fog was temporally variable within a single event and even more so for event-to-event comparisons. The less polluted air masses originated over the Atlantic Ocean, but also showed influence of pollution which they may have picked up during their short travel time along the New England coast. The more polluted air masses traveled a significant amount of time over New England, some of them along the coast, and they probably became contaminated with regional pollution. This pattern explains the high concentrations of fog water compared to other sites in the U.S.A. as well as the high heterogeneity in our data s et.