Atmospheric Transport Model Evaluation

Transport and dispersion was evaluated without any form of tuning by comparing a simulation of the ETEX-1 release to the official measurements of surface concentration. To facilitate comparisons with models evaluated during ATMES 11 (Atmospheric Transport Model Evaluation Study) an identical statistical methodology was employed (Mosca et al. 1998). Background values were subtracted so that only the pure tracer concentration was used. Measurements of zero concentration (concentrations below the background level) were included in time series to the extent that they lay between two non-zero measurements or within two before or two after a non-zero measurement. Hereby, spurious correlations between predicted and measured zero-values far away from the plume track are reduced. 

To evaluate the deposition routines a simulation of the Chernobyl accident was carried out and compared to measurements of total deposited Cesium 137 (Cs-137). The measurements were extracted from the Radioactivity Environmental Monitoring database at the Joint Research Centre, Ispra, Italy (http //rem.jrc.cec.eu.int/). The comparison date was chosen to be 1 May 1986 at 12 00 UTC, since at this time the greatest number of measurements was available. Statistical measures were calculated following the recommendations of the Atmospheric Transport Model Evaluation Study (ATMES) final report (Klug et al. 1992). 

Jacob, D.J., el al., 1997 Evaluation and intercomparison of global atmospheric transport models using mRn and other short-lived traceis. J. Geophys. Res., 102,5953-5970. 

For the evaluation of long-range atmospheric transport and deposition of POPs, a multi-compartment transport model EMEP/MSCE-POP is used (Mantseva et al 2004). It includes such media as the atmosphere, soil, seawater and vegetation (Figure 1). A multi-compartment approach is conditioned by the ability of POPs to be accumulated in soil, seawater and vegetation with subsequent re-emission. Apart from atmospheric transport the model also takes into account the transport of pollutants by sea currents. 

The online coupled model system, Enviro-HIRLAM, which integrates a meteorological model and an atmospheric chemical transport model has been described and evaluated. 

Wright D. L., Kasibhatla P. S., McGraw R., and Schwartz S. E. (2001) Description and evaluation of a six-moment aerosol microphysical module for use in atmospheric chemical transport models. J. Geophys. Res. 106, 20275-20291. 

A large number of explicit numerical advection algorithms were described and evaluated for the use in atmospheric transport and chemistry models by Rood [162], and Dabdub and Seinfeld [32]. A requirement in air pollution simulations is to calculate the transport of pollutants in a strictly conservative manner. For this purpose, the flux integral method has been a popular procedure for constructing an explicit single step forward in time conservative control volume update of the unsteady multidimensional convection-diffusion equation. The second order moments (SOM) [164, 148], Bott [14, 15], and UTOPIA (Uniformly Third-Order Polynomial Interpolation Algorithm) [112] schemes are all derived based on the flux integral concept. 

Atmospheric chemical transport models are evaluated by comparison of their predictions against ambient measurements. A variety of statistical measures of the agreement or disagreement between predicted and observed values can be used. Although raw statistical analysis may not reveal the cause of the discrepancy, it can offer valuable insights about the nature of the mismatch. Three different classes of performance measures have been used for urban ozone models. These tests are heavily weighted toward the ability of the model to reproduce the peak ozone concentrations and include ... 

Using annual emission surveys and trajectory calculations, the concentration, deposition, and transboundary flux of sulphur compounds will be continuously estimated in order to evaluate the atmospheric transport and fate of sulphur dioxide. The model estimates will be compared with the dally measurements at the monitoring stations. 

It is now universally accepted that chemicals of commerce and those that may be formed inadvertently by processes such as combustion should be subjected to evaluation for their possible adverse effects on humans, the environment, and its various ecosystems. Earth surface processes are continually active with atmospheric, oceanic, and terrestrial media forces that foster chemical mobilization with long-range chemical transport within continental land masses, across the oceans, and on a global scale between the hemispheres. Monitoring data from remote locations provide evidence of this transport and these assertions are confirmed by the theoretical results of a variety of multimedia chemical fate and transport models. At the local level, the other geographic extreme, chemical sources are more intense and the pathways shorter and the impacts are therefore more severe. Anthropogenic substances have been mobilized and now exist in every nook, cranny, and recess of the physical environment and within many biological species. 

Atmospheric emissions of sulphur dioxide are either measured or estimated at their source and are thus calculated on a provincial or state basis for both Canada and the United States (Figure 2). While much research and debate continues, computer-based simulation models can use this emission information to provide reasonable estimates of how sulphur dioxide and sulphate (the final oxidized form of sulphur dioxide) are transported, transformed, and deposited via atmospheric air masses to selected regions. Such "source-receptor" models are of varying complexity but all are evaluated on their ability to reproduce the measured pattern of sulphate deposition over a network of acid rain monitoring stations across United States and Canada. In a joint effort of the U.S. Environmental Protection Agency and the Canadian Atmospheric Environment Service, eleven linear-chemistry atmospheric models of sulphur deposition were evaluated using data from 1980. It was found that on an annual basis, all but three models were able to simulate the observed deposition patterns within the uncertainty limits of the observations (22). 

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