Long-Range Transport Models

Some air pollutants are transported far beyond their points of release. For example, otherwise pristine areas have received acid precipitation originating from industrial smokestack emissions hundreds of miles away. Dust from the Sahara Desert in Africa has been detected in South America, and radioactive debris from the Chernobyl nuclear reactor meltdown has been deposited in countries throughout Europe. 

More often in cases of long-range transport, the chemical source is continuous, and the effects of concern are chronic. Consequently, in the process of modeling long-range transport, averaging over long time intervals (often many months) not only is unavoidable, but also is often helpful. Several computer 

FIGURE 4-27 The transport of a cloud of sulfur dioxide emitted from the Cerro Hudson volcano in southern Chile on August 15, 1991. Images are taken from satellite data at 1-day intervals for 7 days. At this scale, the mixing observed cannot be modeled as purely Fickian (otherwise, mass would become more normally distributed about the center of mass) large-scale variability in the wind field clearly influences the shape of the cloud (adapted from Doiron et al, 1991). 

Other regional transport models, such as the Regional Lagrangian Model of Air Pollution (RELMAP Eder et al., 1986), use a different computational scheme than Eulerian models. In a Lagrangian model, the coordinate system moves with a parcel of air and mass balance of pollutant concentrations is computed on a parcel as it moves through space. 

The predictions of such models often can be expressed graphically an example is Fig. 4-28, which predicts the concentration of airborne sulfate 

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Having demonstrated that large areas of critical load exceedance still exist, the final step in the analysis is to predict, using long-range transport models, the amount by which SO2 emissions should be reduced in both Canada and USA so that no... 

Long range transport modelling studies of SO2 in Northern Europe have shown that a "background source of sulphate is required to explain a poor... 

Baklanov A, Sprensen JH (2001) Parameterisation of radionuclide deposition in atmospheric long-range transport modelling. Phys Chem Earth (B) 26(10) 787-799 Bott A (1989a) A positive definite advection scheme obtained by non-linear renormalization of the advective fluxes. Mon Weather Rev 117 1006—1015 Bott A (1989b) Reply. Mon Weather Rev 117 2633-2636... 

Asman WAH, Janssen AJ. 1987. A long-range transport model for ammonia and ammonium for Europe. Atmos Environ 21 2099-2119. 

Eliassen, A. (1978). The OECD Study of Long Range Transport of Air Pollutants long range transport modelling. Atmos. Environ. 12, 479-487. 

Emissions originating from these countries are dispersed over a trajectory intersecting the Balkan peninsula to reach Turkey by the use of a long range transport model. This study is taken from Pervan, T., et al. [5]. A mathematical model (SERTAD, Statistical... 

Gislason, K. B., and Prahm, L. P. (1983) Sensitivity study of air trajectory long-range transport modeling, Atmos. Environ. 17, 2463-2472. 

Particle characterisation can be applied to both core samples and surface sediments to obtain information on the impacts of changes through time at a site or the impacts of contemporary emissions across a region, respectively. Such information is useful for policy formulation and in terms of targeted emission reductions, whether to protect a sensitive environment or the health of a population, source identification for airborne pollutants is vital. Supporting evidence can also be provided for long-range transport models as particulate sources may be identified from external sources (e.g. Davies et al., 1984). 

In the following chapter model refinements are described and compared with the setup used by Gughelmo (2008). The focus is given on the represention of marine organic matter. In a sensitivity study the impact of organic matter on long-range transport is explored. Additionally, a study is included that clarifies the relative importance of sea surface temperature, wind speed, and pollutant concentration for volatilisation of DDT from the ocean. 

The oceanic burden in December 2004 shows the contamination of the ocean after 50 years of PFOA emissions (Figure 3.14). Highest PFOA burden is located in the northern Atlantic, Mediterranean, and the Arctic ocean. Contaminations of the Atlantic, Mediterranean and Pacific can be related to the vicinity to the oceanic source. PFOA in remote regions, however, such as in the Arctic must have been transported via atmosphere or ocean. MPI-MTCM does not simulate degradation of PFOA from volatile, highly mobile precursor substances, that contribute to the ocean burden in the Arctic by deposition. Then annual dry and wet deposition rates of PFOA in the model are small compared to the mass emitted directly to the ocean. This implies that the burden in the Arctic is results mainly from oceanic long-range transport. 

Model results in seawater are in good agreement with observational data of PFOA. Most differences can be attpageributed to deficiencies of the emission scenario. Despite this fact, the difference between model results and observational data are due to the limited horizontal and process resolution and the fact that the physical parameters of the model (temperature, surface pressure, vorticity or divergence of the wind velocity field) were not relaxed to observational data. Regarding these limitations, in particular individual vertical profiles compare quite well with observations. This study underlines the importance of the ocean as a transport medium of PFOA. The contribution of volatile precursor substances to long-range transport needs to be assessed. 

Leip A, Lammel G (2004) Indicators for persistence and long-range transport potential as derived from multicompartment chemistrytransport modelling. Environ Poll 128 205-221 Lin SJ, Rood RB (1996) Multidimensional flux form semi-Lagrangian transport. Mon Wea Rev 124 2046-2068... 

Pekar, M, Pavlova, N. Erdman, L., Ilyin, I., Strukov, B., Gusev, A., Dutchak, S. (1998). Long-Range Transport of Persistant Organic Pollutants. Development of Transport Models for Undone, Polychlorinated Biphenyls, Benzo(a)pyrene. EMEP/MSCE-E Report 2/98. 

Lurmann, F. W., A. C. Lloyd, and R. Atkinson, A Chemical Mechanism for Use in Long-Range Transport/Acid Deposition Computer Modeling, J. Geophys. Res., 91, 10905-10936 (1986). 

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