Forschung (nur Englisch)

  • Sub-tropical atmospheric boundary layers: trace substances and meteorological quantities
  • Laboratory experiments on biogenic nitric oxide emission from soil samples
  • Biogenic emission of nitric oxide: upscaling by emission modelling from field and laboratory studies
  • Biosphere-atmosphere exchange of trace substances: flux methodologies
  • Measurements of biosphere-atmosphere exchange of trace substances on interlinking scales: the Biogeochemistry Department's contribution to the "Large Scale Biosphere Atmosphere Experiment in Amazonia (LBA)"
  • The vector-atmosphere-host interface: the responses of tsetse and other biting flies to host-derived carbon dioxide

Title:

Sub-tropical atmospheric boundary layers: trace substances and meteorological quantities

Investigators:

Franz X. Meixner, Christof Ammann, Grant A. Kirkman, Udo Rummel, Meinrat O. Andreae, Günter Helas (Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, FRG); Willy Maenhaut (Univ. Gent, B); Maria-Teresa Fernandez-Jimenez (Univ. Madrid, E); Stephen J. Torr (NRI Chatham, UK); James R. Milford, Barnabas Chipindu (Univ. Zimbabwe); J.W. Hargrove, Glyn Vale, Pio Chimanga, Jonah Mlambo (IPMI Harare, Zimbabwe); Caxton Ma-tarira (ERSI Harare, Zimbabwe); Harold Annegarn, Lackson T. Marufu, Stuart J. Piketh (Univ. Witwatersrand Johannesburg, RSA)

Summary:

Under the specific conditions of sub-tropical climates, processes of soil-vegetation-atmosphere interaction stringently influence the surface exchange of energy and trace substances as well as the vertical distribution of trace substances in the atmospheric boundary (mixed) layer. Our activities particularly focus (a) surface energy balance studies, and (b) the diel variation of boundary layer structure and its marked influence on the temporal and vertical distribution and transport of trace substances.

In cooperation with our European and Zimbabwean partners, the Biogeochemistry Department performs monitoring of chemical composition of aerosol particles at the Government of Zimbabwe Research Station Rekomitjie (16°09' S, 29°26' E), a very remote site in the Zambezi Valley. Semi-continuous sampling of submicron aerosol particles on stacked filters is performed since September 1994. Samples are sent periodically to University of Gent (Belgium) to be analyzed for their elemental composition by Proton Induced X-ray Analysis. Since 1997, aerosol monitoring activities have been extended by installation of a "streaker" sampler (impaction of aerosol particles on a slowly rotating disk). Temporal resolution of this aerosol analysis is four hours. Ozone and carbon dioxide concentration measurements have been performed in campaign style experiments so far, continuous monitoring is intended.

Continuous aerosol sampling as well as concentration measurements of ozone and carbon dioxide resulted in time series which are characterized by marked diel variations. This could be attributed mainly to local meteorology. Meteorological data were obtained from (a) an automated weather station (extended for the determination of momentum, sensible heat and soil heat fluxes), and (b) vertical soundings by a tethered balloon (0-1000 m above ground) carrying a meteorological as well as lightweight ozone and carbon dioxide sensors. A variety of thermo-orographic effects have been detected (mesoscale channelling, katabatic flows, nocturnal low level jet) which have marked effects on spatial and temporal distribution of trace substances.

Support:

Max Planck Society

Time period:

1994 - 2003

Title:

Laboratory experiments on biogenic nitric oxide emission from soil samples

Investigators:

Saskia van Dijk, Grant A. Kirkman, Franz X. Meixner, Andreas Gut, Michael Welling (Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, FRG); Jos Lelieveld (Univ. Utrecht, NL); Ralf Conrad (Max Planck Institute for Terrestrial Microbiology, Biogeochemistry Department, Marburg, FRG); Luanne B. Otter (CSIR-ENVITEK, Pretoria, RSA); WenXing Yang (SDA-ARS, Fort Collins, USA); Beatriz Machado Gomez (Univ. Rondonia, Ji-Paraná, Brazil); Paul Steudler, Diana Garcia-Montiel (Marine Biological Laboratory, Woods Hole, USA)

Summary:

Laboratory experiments focus on NO emission from soil sampled in various regions of Africa, China and -more recently- in Brazil. Biogenic emissions in these regions are presently big unknowns in estimating global inventories of natural and agricultural NO emissions. In 1996, it could be shown that NO emissions, which were measured in the field (Grassland Research Station, Marondera, Zimbabwe) by use of dynamic chambers agreed noteworthy well with those NO emissions derived by laboratory experiments on corresponding soil samples.

Therefore, under defined laboratory conditions, the final goal of these experiments could be achieved, namely the parameterization of NO emission from soils in terms of its principal influencing factors (e.g., soil moisture and temperature). With the help of this parameterization, seasonal and annual behaviour of biogenic NO emission could be successfully modelled for the Nylsvley Savanna Ecosystem (South Africa) as well as for contiguous Zimbabwe. Results show that the length of the (southern hemispheric summer) wet season is important in determining the amount of NO emitted from a region because of the increased soil moisture and temperature during this time. This is one important reason why tropical regions, with their long hot wet summers, are important globally for the production of NO.

As part of the EUSTACH-LBA programme, current laboratory investigations focus on biogenic NO emission from soil samples of Rondonia (western Brazil). In addition to the African exercise, the influence of soil nutrients and burning status will be also investigated. Results will feed an appropriate NO emission algorithm, which - together with soil temperature, moisture and nutrient models - will be used to predict the desired regional NO fluxes.

Support:

Max Planck Society; European Union

Time period:

1995 - 2003

Title:

Biogenic emission of nitric oxide: upscaling by emission modelling from field and laboratory studies

Investigators:

Grant A. Kirkman, Saskia van Dijk, Andreas Gut, Franz X. Meixner (Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, FRG); Dietmar Schenk (Univ. Mainz, FRG); WenXing Yang (USDA-ARS, Fort Collins, USA); Beatriz Machado Gomez (Univ. Rondonia, Ji-Paraná, Brazil)

Summary:

The catalytic oxidation of atmospheric carbonaceous trace gases by hydroxyl and other radicals generates or destroys ozone in the troposphere. However, the mixing ratio of the key catalyst nitrogen oxides establishes the critical threshhold between ozone destruction (NOx < 30 pptv) and generation (NOx > 30 pptv). While pyrogenic emissions of nitrogen oxides from tropical and subtropical fires have a proven and significant, but seasonally limited impact on the regional and global atmospheric chemistry, the siginificance of the presumably more persistent biogenic fluxes of NO from tropical and subtropical ecosystems of Africa, China and Amazonia is still a fairly open question.

Within recent years, we have developed a laboratory based method (a) to determine the release rate of NO in soil samples, and (b) to parameterize it in terms of the main controlling factors (soil moisture, temperature, and nutrient content). Furthermore, it had been repeatedly demonstrated that NO emissions, which were measured in the field agreed considerably well with those NO emissions derived in the laboratory on corresponding soil samples. Therefore, the laboratory method owns the attractive potential for the determination of regional biogenic NO emission by "scanning" soil samples, provided that area-averaging databases of the main controlling factors are available.

Field and laboratory experiments on biogenic NO emission are long-standing and still ongoing activities of our working group. It is the major task of the present research activity to define, generate and/or evaluate area-averaging databases which are necessary for the application of the NO emission algorithm developed from the field and laboratory activities. Preference is given to already existing data-bases, even those where the needed information could be derived only indirectly. Remote sensing information is used, as well as existing GIS databases. The final purpose is to assemble an entire regional GIS data base, containing the spatial variation in the parameters used to drive NO emission models (based on existing NO emission algorithms). Main target of the present activity are the ecosystems of the Amazon basin (a contribution to the "Large Scale Biosphere Atmosphere Experiment in Amazonia (LBA)"). However, a first application of the described upscaling approach was made to contiguous Zimbabwe. Based on previous field and laboratory work of our group it could be demonstrated, that the contribution of biogenic soil emission to the nationwide NOx budget of Zimbabwe is at least of the magnitude of the biomass burning source.

Support:

Max Planck Society; Graduiertenkolleg Univ. Mainz (DFG); European Union

Time period:

1994 - 2003

Title:

Biosphere-atmosphere exchange of trace substances: flux methodologies

Investigators:

Christof Ammann, Andreas Gut, Robert Kormann, Udo Rummel, Jens Beck, Michael Welling, Eric Simon, Franz X. Meixner, Uwe Kuhn, Jürgen Kesselmeier, Detlev Sprung (Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, FRG); Thomas Foken (Univ. Bayreuth, FRG); Eberhard Schaller (TU Cottbus, FRG); Atsumo Ohmura (ETH Zürich, CH)

Summary:

The Biogeochemistry Department's activities in the field of atmosphere-biosphere exchange concern a variety of trace substances which partially are abundant in (very) low concentrations (e.g., NO, NO2, HNO3, NH3, VOC's, reduced sulfur compounds, size-distributed aerosol particles). It is the main task of the present research activity to improve/develop methodologies to determine corresponding fluxes which comprise the following techniques:

-soil enclosure: a fully automated dynamic soil chamber system is operational and was successfully applied for NO, NO2, and O3 in European, African and Amazonian programmes. Up to 6 individual size-extendible, transparent chambers are sequentially closed and flushed with ambient air by remote control. Operation of one of the chambers as a "blank" chamber ensures the accuracy of the measurements with respect to potential effects of chamber wall losses and gas-phase reactions inside the chambers. Sensors for air/soil tempera-ture, relative humidity, photosynthetically active radiation and soil moisture content are an integral part of the chamber system. The system is used in the Brazilian LBA-programme for NO, NO2, O3, CO2, and H2

-aerodynamic gradient, modified Bowen ratio : the working group's micrometeorological facility comprises several mobile instrumentation suitable for the determination of turbulent fluxes of momentum, sensible and latent heat. Combination with (slow response) non-dispersive infrared (CO2, H2O), UV-spectroscopic (O3), chemiluminescence (NO, NO2), and wet chemical (NH3, HNO3, organic acids) analyzers and sampling systems allow the determination of corresponding trace gas fluxes. Successfull application could be demonstrated for oat and triticale canopies as well as savanna and pasture ecosystems.

-eddy covariance : combination of fast ultrasonic sensors (3D wind speed, temperature) with fast chemical sensors allows the direct determination of corresponding fluxes of trace substances. Successful application has been demonstrated using fast response analyzers, comprising non-dispersive infrared spectroscopy (CO2, H2O), chemiluminescence reaction (O3), tunable diode laser absorption spectroscopy (TDLAS, CH4), and atmospheric pressure ionisation mass spectrometer (API-MS, dimethyle sulfide, H2O). The application to a fast chemiluminescence NO analyzer, to fast optical and condensation particle counters, and to the TDLAS system (N2O, CO) has been performed very recently (see below).

-relaxed eddy accumulation (REA): this technique specifically addresses slow response analyzers and those trace gases where atmospheric sampling based on accumulation techniques has to be performed prior to analytical determination (e.g. VOC's). Ambient air is conditionally sampled via fast response sampling valves into two 'reservoirs' according to the sign of the vertical component of wind velocity. The difference of the concentrations found in the 'reservoirs' is proportional to the turbulent vertical flux of the trace gas. Proportionality is described by the "REA b-factor". During an extended field study over senescent triticale our REA system (CO2 and H2O) was thoroughly compared to eddy covariance, energy balance and aerodynamic profile systems for a wide range of environmental conditions, particularly under conditions of stable stratification . An outstanding result is the first concise description of the "REA b-factor" within the framework of the Monin-Obukhov-similarity-theory for the entire stability regime.

-in-canopy profiles/Inverse Lagrangian Modelling: concentration profiles and turbulence characteristics are measured within a given canopy structure. With the help of Inverse Lagrangian Modelling vertical distribution of sinks/sources of trace gases can be derived from the measured profiles. Successfull application for sensible heat, CO2 and H2O fluxes could be demonstrated for a senescent triticale canopy.

-(nocturnal) surface layer mass balance: any trace gas exchange at the Earth's surface creates local concentration surplus or deficit in the adjacent air layers, notably in the surface layer. A mixed surface layer represents a well mixed closed chamber which is -especially in the nighttime case- topped by an temperature inversion. Like in the chamber case, the surface flux is determined by the temporal change of the vertically averaged trace gas' concention and the height of the boundary layer. This approach was successfully applied to the surface exchange of carbonyl sulfide for a Californian oak-lichen-soil ecosystem.

Support:

Max Planck Society; Bundesministerium für Forschung und Technologie (BMFT); EUROTRAC-BIATEX

Time period:

1994 - 2003

Title:

Measurements of biosphere-atmosphere exchange of trace substances on interlinking scales: the Biogeochemistry Department's contribution to the "Large Scale Biosphere Atmosphere Experiment in Amazonia (LBA)"

Investigators:

Franz X. Meixner, Christof Ammann, Andreas Gut, Robert Kormann, Udo Rummel, Michael Welling, Jens Beck, Greg Roberts, Pascal Guyon, Uwe Kuhn, Stefanie Rottenberger, Tom Biesenthal, Günter Schebeske, Anette Wolf, Jürgen Kesselmeier, Günter Helas, Meinrat O. Andreae, Jörn v. Jouanne, Horst Fischer (Max Planck Institute for Chemistry, Mainz, FRG); Roberto Lyra, Marcos Moura, Ednaldo Oliviera (Univ. Alagoas, Maceio, Brazil); Sergio Oliva, Tania Tavares (Univ. Bahia, Salvador, Brazil); Beatriz Machado Gomez (Univ. Rondonia, Ji-Paraná, Brazil)

Summary:

Land-surface heterogeneity is a major challenge to both, the measurement and the modelling of biosphere-atmosphere exchange of energy, water, momentum, and trace substances. In case of measurements, the challenge regards the development of new measurement techniques (at a variety of scales) and the re-conciliation of flux measurements at different scales. The Biogeochemistry Department's contribution to the LBA programme fits in this context. For a primary rainforest and a pasture ecosystem in Rondonia (western Brazil) the attempt is made to measure and to interpret (to model) biosphere-atmosphere exchange processes in (heterogeneous) terrain at interlinking spatial scales from soil and leaf up to ecosystem.

The primary objective of our study is the determination of diel and seasonal exchange of aerosol particles, CO2, H2O, CO, biogenic VOC's, NO, NO2, and O3. Biogenic volatile organic compounds may comprise isoprene and monoterpenes, short-chain aldehydes, and optionally organic acids, alcohols, and acetone. Measurements address soil-atmosphere exchange, in-canopy processes, and net fluxes above the canopy.

The surface exchange of biogenic VOC's, CO, O3, NO and NO2 will be performed by an integrated experimental approach, using soil/leaf/twig/branch enclosure/cuvettes, in-canopy concentration profile measurements (followed by Inverse Lagrangian Modelling) and micrometeorological techniques (aerodynamic profile, relaxed eddy accumulation, eddy covariance). The flux of aerosol particles over the forest is obtained by an eddy covariance technique (fast optical and condensation particle counters).

All measurements of trace gas exchange on the soil chamber and cuvette level are tied to the determination of soil nutrients and to continuous measurements of soil temperature, soil moisture, the photosynthetically active radiation, the absolute CO2 concentration in the air, the CO2 exchange (photosynthesis) as well as of water transpiration of the enclosed vegetation elements. Thus we will (a) obtain suitable parameters to describe the exchange of the corresponding trace gases in terms of their driving processes and (b) get insight into the coupling of physiological activity (photosynthesis, transpiration, stomatal conductance) and the emission or deposition of the trace gases.

To address problems of (a) in-canopy storage fluxes of trace gases, and (b) photochemical interconversions of the triad NO-NO2-O3 within the canopy, vertical profiles of in-canopy concentrations will be obtained by drawing air via PTFE tubings from several heights through a remote controlled manifold into the corresponding analysers. In case of NO-NO2-O3, these profile measurements are needed in particular, because the NO and NO2 fluxes measured above the canopy may be biased by in-canopy conversion of biogenic NO (originating from the forest floor) through O3 (mixed into the forest canopy from aloft) to NO2 . The effect of fast chemical reactions (NO-NO2-O3) on the turbulent above-canopy NO, NO2, and O3 fluxes will be corrected by simultaneous measurement of the NO2 photolysis rate, j(NO2), and the application of suitable diagnostic models. Fluxes of VOC's will be obtained by relaxed eddy accumulation technique, while O3 and NO fluxes are determined by eddy covariance.

Support:

Max Planck Society; European Union

Time period:

1998 - 2003

Title:

The vector-atmosphere-host interface: the responses of tsetse and other biting flies to host-derived carbon dioxide

Investigators:

Gabriela Zöllner, Stephen J. Torr (Natural Resources Institute Chatham/ University of Greenwich, Department of Pest Management, UK); Franz X. Meixner, Christof Ammann (Max Planck Institute for Chemistry, Biogeochemistry Department, Mainz, FRG)

Summary:

Biting flies transmit a range of animal and human diseases with massive medical, economic and social impact. These flies locate their hosts using host odours, in particular carbon dioxide, and the olfactory responses of biting flies have been exploited by developing various odour-baited traps and targets to control or monitor disease vectors (e.g., tsetse fly, the vector of sleeping sickness in man and Nagana in cattle). The success of bait technology for tsetse has led to widespread interest in developing similar systems for controlling other disease vectors. Accordingly, there is great interest in understanding the structure and behaviour of host-odour plumes and the responses of insects to these plumes.

An insect's response to host carbon dioxide is particularly complex because of the natural presence of relatively high levels of carbon dioxide in the atmosphere. Consequently, an insect's probability of contacting a host is dependent on the amount of carbon dioxide produced by a host, the back-ground "noise" of atmospheric carbon dioxide and the sensitivity of an insect's carbon dioxide sensory apparatus. Although interest in quantifying odour plumes addresses biological questions concerned with animal behaviour, the methods of quantifying odour plumes belongs to the field of atmospheric physics (micrometeorology). There is thus a need for a multidisciplinary approach to the problem.

Since 1992, NRI and MPIC have undertaken collaborative studies at Rekomitjie Tsetse Research Station (Zimbabwe). During campaign style experiments sensitive and fast response (<0.1 s) CO2 measurements are performed in natural tsetse habitats. During the dry season, the level of background noise of CO2, against which host CO2 is detected, is surprisingly low (< ±0.5 ppmv over 5 min averaging periods). Simultaneous fast response measurements of CO2 concentration, air temperature, wind speed and -direction focus the dispersion and structure of the odour plume. Classical micrometeorological techniques are applied to study the influence of surface layer stability on plume dispersion within the canopy.

Support:

British-German Academic Research Collaboration Programme (DAAD-ARC); Max Planck Society

Time period:

1997 - 2001