Atmospheric diffusion modelling
A second-generation Gaussian atmospheric diffusion
model (Atmospheric Dispersion Model System version 3
– ADMS 3) was used to compute "immission" estimates
(immission is the amount of pollutant reaching a particular
location as a result of – and in contrast to – the emission
coming out the chimney) for each category of
pollutants (dioxins, metals, dusts) in the surroundings of
MSWIs (from 5 to 20 km, depending on the incinerator)
[19]. The dispersion modelling methodology used a
receptor grid spacing of 200 m. Parameters considered
were the quantitative estimates obtained above from the
experts, chimney height and diameter, plume emission
temperature, particle size and density, topographic indicators
(roughness, relief), local weather data, etc. The latter
came from the national meteorological agency (Météo
France). Immission estimates served as proxies for annual
ambient air concentrations of chemicals attributable to
the MSWI at a given location.
Exposure of communities (block groups)
Population exposure to pollutants emitted by MSWIs was
estimated only as a function of the geographic zone of residence.
The immission estimate assigned to each of the
2270 communities was the median of all receptor estimates
located in each block group (the mean block group
surface was 9.45 km2, corresponding on average to 231
receptors). When a community was under the plume of
several MSWIs, the exposure index was defined as the sum
of the estimated indexes of each. We calculated two different
exposure indexes for each community, according to
different hypotheses about the mode of exposure: (1) the
immission estimate alone represented exposure from
inhalation only (expressed in ng/m3); (2) this score was
transformed to account for the number of years the plant