Konferenzbeitrag
Evaluating the Long-range Transport of Persistent Organic Pollutants – Computation and Analysis of Air Mass Backward Trajectories
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2005
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Masaryk University Brno
Zusammenfassung
Persistent organic pollutants (POPs) are present in all environmental compartments. Most of them are products of human activities, however a small part of some POPs is of natural origin. They are lipophylic and therefore accumulate in organisms. A problem is also the fact that some of their metabolites and products of degradation processes are of a more dangerous character than the original pollutant. POPs are subject to long-range transport, mainly in the atmosphere.
We can use mathematical models to describe the movement of POPs and other pollutants inside of single environmental compartments and between them. In case of the atmosphere it is possible to use dispersion models which evaluate the transport, dispersion and transformation of pollutans from the known source. We can also use different types of receptor models to describe the situation at a receptor (sampling) site. Receptor models can be used if there is only an uncomplete or inaccurate inventory of sources available or the existence of unknown sources is supposed. Both models are very often based on the analysis of forward or backward air mass trajectories.
A trajectory is the path of an imaginary air parcel as it is acted on by winds. There exist different ways of computation but all of them require meteorological data computed or measured regularly during the whole time of considered air mass transport. The accuracy of a computed trajectory depends on the spatial and temporal resolution of meteorological observations, errors in data measurement and analysis and simplifying assumptions. Also, the longer a trajectory is, the less accurate it is.
Air mass trajectories used in our study were calculated using the HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model developed by the Air Resources Laboratory of the American NOAA (National Oceanic and Atmospheric Administration) which is available free of charge on their READY website.
Backward trajectories were calculated to examine the situation at the regional background observatory Košetice (Pelhřimov district, Czech Republic) which is a part of EMEP (Co-operative Programme for Monitoring and Evaluation of the Long-Range Transmission of Air Pollutants in Europe). The study focused on 16 according to EPA prior polycyclic aromatic hydrocarbons (PAHs), seven polychlorinated bifenyls (PCBs), four isomers of hexachlorocyclohexane (HCH), dichlorodiphenyl trichloroethane (DDT) and two metabolites, hexachlorobenzene (HCB) and pentachlorobenzene (PeCB).
There exist various ways of evaluating backward trajectories. To examine the direction from which the most polluted air masses arrived it is possible to use the EMEP „sector“ method. These results can be supported by determining countries over which territories these air masses traveled. Other simple methods include the residence time analysis, identification of subsets of trajectories associated to air masses of a specific air quality or statistics methods. The last three mentioned methods require gridding the considered area into regular cells and evaluating the abundance of trajectory endpoints within them. Here the geographic information system (GIS) comes into use together with the ArcGIS 8 computer programme and its special modules for data processing. The results can be presented in form of tables, graphs and also maps showing areas over which polluted air masses traveled and which have led with 1 RECETOX, Masaryk University, Kamenice 3/126, CZ-62500 Brno, email: dvorska@recetox.muni.cz, Internet: http://www.recetox.muni.cz 980 some probability to increased pollutant concentrations measured at the receptor site. It is useful to compare the results with already existing knowledge on industrial or agricultural areas too.
Data from the observatory Košetice for the years 1999 to 2001 were already evaluated by the EMEP method – we found the western sector to be dominant for more polluted air masses and this is in agreement with general meteorological conditions for the Czech Republic too. Also the states were previously roughly evaluated and except our neighbouring countries also France was more abundant.
The analysis of air mass trajectories helps to reveal connections between the meteorological activity and measured ambient air quality parameters. Evaluating backward trajectories also helps to identify pollutant sources and/or areas which is the first step when developing effective pollutant control strategies. Revealing air mass transport patterns for a background station like Košetice is also useful for the characterization of atmospheric long-range transport for a whole region.