tailieunhanh - Approaches to Scaling of Trace Gas Fluxes in Ecosystems

Emission inventories play a dual role in global air pollution issues. Firstly, they can be used directly to establish the more important source categories, to identify trends in emissions and to examine the impact of different policy approaches. Secondly, emission inventories are used to drive atmospheric models applied to assess the environmental consequences of changing trace gas emissions and concentrations and to provide advice to policy makers. This second role contributes to the atmospheric modelling community being an important user of emission inventories. The assessment process for global air pollution problems has a number of identifiable steps: (i) it quantifies the changes in trace gas composition of. | Developments in Atmospheric Science 24 8OUWMAN otflor Approaches to Scaling of Trace Gas Fluxes in Ecosystems Vll FOREWORD The world s terrestrial and aquatic ecosystems are important sources of a number of greenhouse gases and aerosols which cause atmospheric pollution and disturb the energy balance of the Earth-atmosphere system. In recent decades the measurement techniques and instrumentation for quantifying gas fluxes have been improved considerably. Yet the uncertainties in the regional and global budgets for a number of atmospheric compounds have not been reduced due to the large spatial heterogeneity and temporal variability of the factors that control gaseous fluxes in ecosystems. Techniques used for extrapolating measurements or properties and constraining results between different temporal and spatial scales are nowadays referred to as scaling . All scaling methods are embedded in the data. Apart from uncertainties associated with the data used errors may be caused by generalization of the basic data . in soil maps ocean maps . Moreover much of the spatial and temporal variation at a detailed level is obscured as a result of aggregation. Possible errors caused by the use of aggregated or generalized data in models are generally not explicitly analyzed. An important step in scaling of gas exchanges between ecosystems and the atmosphere is the delineation of functional types where distinct differences in structure composition or properties of landscapes or water bodies coincide with functions or processes relevant for gas fluxes. Delineation reduces the variability of state variables and therefore functional types form a good basis for measurement strategies and model development. Models are widely used tools in bottom-up scaling approaches. Models can also be used to calculate flux values for regions where less intensive or no measurement data are available. One of the challenges in model development is the integration of properties or variables in