How setting 'emission limits' prevents nuisance

IntroSite specific odour emission limits, determined through source quantification and dispersion modelling, provide a useful tool for determining planning and permit conditions and ensuring the risk of odour nuisance is minimised. Morgan Fitzpatrick, a consultant at OdourNet UK, the environmental odour consultant, explains how this approach works

Historically the approach to odour nuisance has been a reactive one, but the new IPPC regime is now making sure that a much more pro-active approach is taken to controlling this nuisance. The IPPC application process has placed greater odour assessment and monitoring demands on both operators and regulators and as a result of the raised profile accredited odour analysis laboratories and impact assessment techniques are in demand. The introduction of guidance specific to the subject matter (eg Environment Agency Horizontal odour guidance H41 and supporting research), and the availability of laboratories capable of measuring odours in compliance to standards recognised by UKAS, means that a robust set of tools for determining permits now exist.

By the time odour complaints are being registered by a local authority or installation it is likely that a large number of people have been experiencing annoyance for some time. In fact studies have shown that "no complaints do not necessarily mean no annoyance". Needless to say that annoyance within the community reflects poorly primarily on operators but also on local authorities. The IPPC permitting regime takes a firm line in this matter with the aim of minimising odour emission, within the realms of BAT, to the point of "no reasonable cause for annoyance".

"Permit conditions" are a useful enforcement tool to prevent annoyance occurring in the community. Used effectively permit conditions such as "Odour emission limit values" can provide a proactive and transparent method to control and monitor the release of odour into the environment.

The scientific basis underpinning regulation of odours involves quantification of odour by olfactometry and impact assessment using atmospheric dispersion modelling. It is through these scientific techniques that emission limit values should be determined.

Assessment process

The assessment procedure generally follows the following stages:

  • Conduct an odour audit to identify potential sources and the process variables that can influence emissions from these sources. (including accidents and abnormal operations).
  • Quantify the odour emissions from each source and under each operational condition, using suitable techniques. For emissions which are limited to single specific odorants, it may be possible to quantify odour in terms of the concentration of that chemical. However, for most odorous emissions that contain more than one odorant, the preferred measurement technique is olfactometry analysis. It is imperative that analysis is carried out by a UKAS accredited laboratory to the CEN standard for Olfactometry 13725.
  • Determine the level of exposure to which sensitive receptors are exposed under all operational conditions, using suitable dispersion modelling techniques.
  • Determine whether and where a risk of impact exists, by application of suitable odour annoyance criteria (eg Annex 6 H4), and determine the level of reduction in emissions required to prevent/minimise such impact (from published guidance or by a general review of the appropriate literature).
  • Identify the Best Available Techniques to achieve the reduction. Adoption of this staged approach meets the fundamental requirements of the IPPC Regulations, and provides data that can be used directly or indirectly in defining specific odour emission limits for specific plant, or definition of process control parameters for specific plant to be translated into Licence conditions. Once an emission limit value is determined routine compliance monitoring is cheap and provides interested parties with the confidence that there is not a rash of odour complaints on the horizon. In OdourNet's experience, this general approach is equally effective when applied to inform planning applications, or to assess, justify or dispute nuisance allegations.
1. Horizontal Odour Guidance H4, available from



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