Search

link to homepage

Institute of Energy and Climate Research

Navigation and service


Contributions of the partners

  • In the subproject proposed by the Research Centre Jülich the emissions of volatile organic compounds (VOC) from the different tree species at the field site (Stetternicher Forest, Jülich, Germany) will be measured. In parallel, experiments in plant chambers under defined conditions will be done in order to quantify the primary emissions of these compounds. In addition, their uptake by the plants will be investigated. The objective of these experiments is making emission algorithms available for later modelling. In two intensive field campaigns it will be investigated with which oxidizing agents (OH, HO2, NO3, O3) VOC react predominantly in the canopy and to what extent photochemistry or night time chemistry (e.g. ozonolysis and reactions with NO3) contribute to the oxidation of VOC. For this purpose it is planned for the first time to measure the concentration of radicals (OH, HO2, RO2, NO3), a large set of trace gases (VOC, CO, O3, NOx, organic nitrates), and meteorological parameters at different heights in and above the forest stand.
    In order to quantify the photochemical activity in the forest stand, for the first time the solar actinic flux in the visible and ultraviolet will be measured spectrally resolved to derive photolysis frequencies of relevant radical precursors (O3, NO2, peroxides, oxygenated VOC). The chemical processing of the trace gas mixtures observed in the forest stand will be simulated in the atmosphere simulation chamber SAPHIR under controlled conditions. In the simulation experiments the same trace gases and parameters are measured as in the field experiments under application of the same equipment. This enables on the one hand the detailed study of the chemical processes under exclusion of transport processes and on the other hand sensitivity studies by direct modification of individual chemical parameters.The observations of the field experiments and of the simulation experiments will be compared further with chemical box model calculations. With the combination of field and simulation experiments it will be tried to quantify the chemical processing of the VOC, the photo-oxidant formation in the forest and the radical balance.
  • The Max Planck Institute for Chemistry will investigate the release of VOC and NOx species as well as their fate within the atmosphere. Gaseous and reactive compounds, once emitted, are not easily quantified within the atmosphere as they underlie fast oxidative transformation processes. Quite often the products are unknown and/or end up within or on particles. Therefore, to quantify the total VOCs we will combine different investigation and techniques with enclosure methods to perform analyses on the leaf and branch level as well as with mesoscalic integration by micrometeorological methods. Such a combination will give access to primary emissions and secondary fluxes. This work will be closely coupled to the investigations of processes of air chemistry (radical chemistry) and aerosols as planned within the Joint project. An interpretation of the influence of VOC onto the oxidation capacity of the atmosphere is impossible without knowing the NOx-concentrations or the biogenic NO source strength of the soil, respectively. Complementing the studies of primary emissions and of VOC fluxes we will therefore perform intensive investigations of the biogenic NO-release from forest soils as well as of the vertical distribution of NOx and its turbulent transport within and above the forest.
    The combination of the different techniques and procedures for the determination of primary emissions, atmospheric concentrations and the fluxes will allow a better interpretation of biogenic emissions and their influence on the atmosphere. A high time resolution (1/s) of a new measuring technique for VOCs, the AP-CIMS technique, will provide accurate diurnal patterns and will give access to the short time variations of primary emissions. Furthermore, measuring organic acids will contribute to the understanding of the production processes and compositions of secondary organic aerosol. Quantification of biogenic NO-Emission, the understanding of the production controls (soil moisture and temperature, composition), the knowledge of the vertical NOx-distribution and transport within and above the forest will build up a fundamental understanding of the oxidation processes, to which VOCs, radicals and NOx are contributing in a very complex manner. Hence, measuring the primary emissions of trace gases and their fluxes will help to produce a budget in order to verify the physical and chemical transformation processes within and above the forest and the amount and quality of the trace compounds released into the background atmosphere in reality.
     
  • The role of ISAS Dortmund within the overall project is focused on the investigation of the atmospheric degradation of the reactive natural VOCs in connection with their potential to form aerosols. Although the aerosol formation potential of biogenic VOCs as a consequence of the gas-to-particle conversion of their oxidation products is a well known phenomenon, detailed investigations in the field are lacking. The studies realised up to now concentrated essentially on the determination of the aerosol yields of biogenic and anthropogenic VOCs and the identification of gas and particle phase oxidation products in laboratory studies, indicating that the amount of organic aerosol formed strongly depends on the initial oxidation step (OH, NO3 or O3) as well as the temperature.
    Unfortunately, field studies considering these processes and therefore a validation of the lab results are rare, especially in anthropogenically influenced regions with a high variation of the actual NOx and ozone concentrations which affect the routes to the formation of low volatile species. Therefore, the attempt to close the mass balance of tropospheric organic compounds still fails due to a missing understanding of the processes. In order to answer these questions, the following measurements are planned:
  1. Gradient measurements of biogenic VOCs and some of their oxidation products above a mixed forest in the vicinity of Jülich.
  2. Time resolved chemical characterisation of the organic particle phase, especially focussing on secondary organic aerosol components.
  • The Meteorological Institute Hamburg of the University of Hamburg will deliver new information on vertical transport phenomena in the lower layers of the Troposphere. The horizontal and vertical transport of tracers above a biogenic area source (finite forest area) will be modelled in a large boundary layer wind tunnel. Systematic investigations consisting of detailed high resolution flow and dispersion measurements will be carried out to extend the field data and to quantify reliability and representativeness of corresponding field measurements in space and time.
    The project directly contributes to quality assurance of field data and their enhancement in terms of extending the database for situations that could not be measured in full scale. Field and laboratory data together will lead to a high quality data set for model validation purposes. The sub-project is part of the project cluster ECHO which aims on a better understanding of the role of a forest stand as a complex source of volatile organic compounds on the climate system. The specific objectives of our sub-project are
  1. support in effective planning of the field measurements done by the FZ Jülich group (repeating specific aspects of the field experiments in the new boundary layer wind tunnel, optimising and validating the location of sampling points for field measurements in terms of reliability of the results and their representativeness in space and time for different wind directions/wind speeds)
  2. complementing field data with additional laboratory data for adjacent emission situations not captured during field data campaigns (extending the database by adding data for additional wind directions, different emission characteristics, measuring horizontal and vertical transport of momentum and species above the emitting area)
  3. quantifying the variability of field data due to the variation of boundary conditions (quantifying the reliability of field data which is required for comparing the field data with results from numerical dispersion modelling)
  4. compiling an extensive and completely documented set of reference data consisting of field data and high quality laboratory data. Publication of all results in an electronic database as well as in reviewed journals.

Servicemeu

Homepage