Odour impact assessment

Assessment of the extent to which odour impacts can be expected from industrial and agricultural facilities is increasingly required as part of planning applications, applications for IPPC authorisations, and to demonstrate the adequacy (or otherwise) of odour management and control techniques.

The procedure requires an estimation to be made of the total odour emissions from the facility in question, and the use of atmospheric dispersion modelling techniques to predict the level of exposure of odours in the surrounding community. By application of a suitable odour annoyance criterion, the area where annoyance (which may lead to complaints of nuisance) may occur can be determined. This information can be used to ratify odour annoyance complaints, predict the likely impact of new and existing facilities, and to evaluate control strategies in order to identify the most cost-effective solution for a particular activity.

Source characterisation
Odorous emissions from the facility under investigation can be characterised by measurement of emissions at source, using sampling and analytical method according to the European standard for olfactometry CEN EN 13725 (2003) or for diffuse sources, by application of field assessment techniques. Alternatively, emission factors measured at similar sources, or those from research, may be applied for proposed developments. Odournet has a substantial database of emission estimates from a wide range of industrial and agricultural operations.

Determination of exposure
The process that leads from an odorous emission to actual odour annoyance is not straightforward; it involves a number of factors such as the character of the odour, dilution in the atmosphere and factors relating to the location and sensitivity of the receptors. Some or all of these may need to be examined in detail when assessing the odour impact of a facility.
Currently, the most robust methodology for assessment of the levels of exposure from odorous processes is to utilise atmospheric dispersion modelling techniques. Through careful consideration, an appropriate odour criterion (expressed in terms of concentration and frequency of exposure e.g. 5 ouE/m3 98th percentile) can be applied to the output of the dispersion model to predict the area where odour annoyance may occur. These criteria can be derived either by epidemiological dose-effect studies, or by analysis of complaint behaviour at specific facilities.

Applications
Once the emissions from a specific facility have been characterised, it is possible to use the impact model to assess variations in the emissions characteristics to identify means by which the extent of impact can be reduced. This information can be used to evaluate mitigation options, compare and contrast changes in process or odour control strategy, and demonstrate the impact of new facilities or improvements resulting from refurbishment of existing facilities. The use of such desktop assessment procedures provide a useful and cost effective means of evaluating process options at the design stage, avoiding problems later on in the project.


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