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  • Report n°4: How Much to Spend for the Protection of Health and Environment

Report n°4: How Much to Spend for the Protection of Health and Environment

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    • Impact Pathway Analysis (IPA)
      • Dispersion of Pollutants and Exposure

Dispersion of Pollutants and Exposure

The principal greenhouse gases, CO2, CH4 and N2O, stay in the atmosphere long enough to mix uniformly over the entire globe. No specific dispersion calculation is needed but the calculation of impacts is extraordinarily complex and here I refer merely to the main authority, the Intergovernmental Panel on Climate Change [IPCC http://www.ipcc.ch]. For most other air pollutants, in particular PM10 (particulate matter with diameter less than 10 mm), NOx and SO2, atmospheric dispersion is significant over hundreds to thousands of km, so both local and regional effects are important. ExternE uses therefore a combination of local and regional dispersion models to account for all significant damages. The main models for the local range (< 50 km from the source) have been the gaussian plume models ISC [Brode & Wang 1992] for point sources such as power plants, and ROADPOL for lines sources (emissions from transport) [Vossiniotis et al 1996].

At the regional scale one needs to take into account the chemical reactions that lead to the transformation of primary pollutants (i.e. the pollutants as they are emitted) to secondary pollutants, for example the creation of sulfates from SO2. Here ExternE uses the Windrose Trajectory Model (WTM) [Trukenmüller and Friedrich 1995] to estimate the concentration and deposition of acid species. WTM is a user-configurable Lagrangian trajectory model, derived from the Harwell Trajectory model [Derwent and Nodop 1986]. The modeling of ozone is based on the EMEP MSC-W oxidant model [Simpson et al. 1992, Simpson and Eliassen 1997]. EMEP is the official model used for policy decisions about transboundary air pollution in Europe.

The calculation of damage costs is carried out by means of the EcoSense software package [Krewitt et al 1995], an integrated impact assessment model that combines these atmospheric models with databases for receptors (population, land use, agricultural production, buildings and materials, etc.), dose-response functions and monetary values. Joe Spadaro has also developed a simplified analysis tool, called RiskPoll (actually a package of several models with different input requirements) and freely available from www.arirabl.org or www.externe.info. It is based on the interpolation of dispersion calculations by EcoSense, and with its simplest version yields results that are typically within a factor of two to three of detailed EcoSense calculations for stack heights above 50 m. RiskPoll includes a module for the multimedia pathways of Fig.2.

Several tests have been carried out to confirm the accuracy of the results. For example, we have checked the consistency between ISC and ROADPOL, and we have compared the concentrations predicted by WTM with measured data and with calculations of the EMEP program, the official program for the modeling of acid rain in Europe. We have also found good agreement between EcoSense and measured concentrations [Rabl et al 2004b].

Whereas only the inhalation dose matters for PM10, NOx, SO2 and O3, toxic metals and persistent organic pollutants affect us also through food and drink. For these a much more complex IPA is required to calculate ingestion doses. Spadaro & Rabl [2004] have developed a model for the assessment of external costs due to the emission of the most toxic metals (As, Cd, Cr, Hg, Ni and Pb), as well as certain organic pollutants, in particular dioxins. It takes into account the pathways in Fig.2. The output of this model is the damage per kg of pollutant, as a function of the site and conditions (for emissions to air: stack height, exhaust temperature and velocity) of the source. The model is based mostly on transfer factors published by EPA [1998], with some supplemental data of IAEA [1994 and 2001]. These transfer factors account in a simple manner for the transport of a pollutant between different environmental compartments, for example the uptake by agricultural crops of a pollutant from the soil. The uncertainties are large, but at least one has approximate values for the pollutants of concern here.

We do not yet have all the elements for calculating the dose due to ingestion of seafood, potentially large because of bioconcentration and because most fish comes from the ocean rather than freshwater. Even if the concentration increment in the sea is very small, the collective dose from seafood could be significant if the removal processes (sedimentation) are slow and the analysis has no cutoff in time.

A general result of this analysis is that when these pollutants are emitted into the air, the ingestion dose can be about two orders of magnitude larger than the dose by inhalation. Because nowadays most food is transported over very large distances, the total dose varies very little with the site where these pollutants are emitted into the air. As far as damages are concerned, one has to note that the same dose can have a very different effect on the body depending on whether it is inhaled or ingested. Cd, Cr-VI and Ni, for instance, are according to current knowledge carcinogenic only through inhalation.