The equal-intensity events special case models of odour
annoyance provide robust logical frameworks within which
detailed analyses may be undertaken of the efficacy of threshold
and percentile based odour criteria to predict and limit annoyance.
Models in which both the frequency and intensity of impact
events are assumed to be associated with annoyance highlight
what appear to be significant shortcomings in the efficacy of single
percentile odour criteria to predict nuisance odour impact extents.
Consideration of these models suggests that a multi-percentile
approach may significantly mitigate these shortcomings, however
more sophisticated approaches may ultimately be required to
maximise skill of dispersion modelling to predict nuisance odour
impact extent.
Compared to single percentile criteria, the suggested multipercentile
approach allows for a wider range of meteorological
conditions that may be important in terms of impacts to influence
calculated separation distances. This attribute may potentially aid
resolution of a noted disparity between complaints data and some
single percentile model calculations (Schauberger et al., 2008).
These models also strongly support a particular interpretation of
the community annoyance curve concept proposed by Watts and
Sweeten (1995) that resolves difficulties with an alternative interpretation
of this concept suggested by Wallis and Cadee (2008).
The analysis undertaken in this paper suggests that the identified
short-comings of single percentile criteria and differences in
impact environments at study locations may have been contributing
factors to some seemingly disparate dose response study
findings. The reviewed empirical data appear to be broadly
consistent with this hypothesis, but are not conclusive.
The models of annoyance developed here and the regulatory
definition of nuisance odour proposed by Watts and Sweeten
(1995) address the question of which percentile is “best” for
describing odour exposure, however they raise new questions
which require resolution. These relate to the limits of the range of
event frequencies or percentiles to be considered in models of
annoyance, the nature of adverse community response incurred at
these percentile levels and the significance of additive effects when
thresholds are approached or exceeded at multiple percentile levels
in multi-percentile approaches.
While shortcomings of single percentile odour criteria have
been previously identified by a number of researchers, to date these
shortcomings have been largely overlooked by regulators. It is
suggested that this earlier work, in combination with the models of
annoyance developed here provide an improved concept of odour
criteria that may assist in the development more skilful and better
harmonised jurisdictional criterion frameworks.