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Odours are ranked as the main generators of public complaints by regulatory agencies in Europe, North America, and Australia.
'Air Quality Regulations and Odour Management in Australia and New Zealand' provides a summary of the standards and air pollution legislation existing in Australia. Odourous emissions from waste treatment and management and intensive livestock operations often cause annoyance to local receptors, impacting quality of life, resulting in public complaints for regulatory agencies that require appropriate management responses. Within communities, there is often a large range of reactions to odourous emissions. On the one hand there are receptors that are very sensitive to specific odors (i.e. highly odour-sensitive) and will react very strongly to odours that are barely noticeable by the majority of the population. On the other hand there are other receptors within a population (often because of their association with the odour-generating activity) who are more tolerant to these odour annoyances.
Below are limits set in various states:
0.5 OU for tall stacks
2.5 OU for ground level sources and down washed plumes from short stacks. These criteria have been developed based on a 5 OU short term impact and have been translated to a one hour averaging time using a peak-to-mean ratio of 10:1 for tall stacks and 2:1 for other sources 1-hour average, 99.5% percentile
Individual odorous pollutants In the case of hydrogen sulfide
2 OU (2000 people or more); 4 OU (350-1999 people); 6 OU (60-349 people); 8 OU (12-59 people); 10 OU (less than twelve people)
Offensive odors must not be discharged beyond the boundaries of the premises.
2 OU or 4 OU
Odorous emissions from anthropic activities often cause annoyance to local receptors, impacting community quality of life, resulting in public complaints for regulatory agencies that require appropriate management responses. A major challenge for regulatory agencies is to provide community protection from offensive odours without unfairly disadvantaging odour-emitting industries that communities often rely on for their economic prosperity
There are five main stages in an air quality impact assessment:
Sets out guidance for modeling of air quality impacts (including odour). Dispersion modeling uses a computer model to calculate likely odour level at a receptor (this could be something that is going to be built or something that is there already. This done my estimating how odorous the source (chimney / farm yard for example) and then applying weather to the model, such as prevailing north westerly winds as typical in Sydney.
The weather and the sources are then "mixed" in the model and any number of figures can be generated for levels of odour (concentrations) at the receptor location. The NSW guide recommends the use of AUSPLUME Modelling software, although AERMOD is now a generally accepted dispersion model world wide, as it is frequently updated, and many modeling software packages use the AERMOD program (executable) as there underlying engine.
The guide sets out some use details on the acceptable concentrations for odorous substances, and sets ou the two levels of acceptable odour assessment:
Is a screening-level dispersion modeling technique using worst-case input data. If a concern has been raised by planning authorities it is likely that a screening assessment will trigger a requirement for a full (level 2) assessment. This is because screening assessment rely on very conservative (far above worst case) values, and as such if you have identified a site which may have an odour problem (based on common sense) it is unlikely it will screen out with a Level 1 Assessment.
Would involve a detailed modeling of the site, which for the most part are the methods described in this page.
Acceptable odour level are set based on the number of people they will affect, simply put, if you proposal will see many people effected then the allowable odour level will be low. If however, your proposal will not affect many people then allowable odour levels are higher:
So in summary if you live in a community of 500 people or more you amenity is protected to an extent where it will not be impacted by new proposals creating odour, however for other in smaller communities, impacts can be noticeable, and if odors are unpleasant have a high impact and still be allowable under the NSW Guide.
We have recently completed an Odour Impact Assessment for a site to the South of Sydney. Our clients were looking to establish an intensive arable agribusiness, which could have potentially created negative odour impacts. We have researched the process include growing medium, and ventilation requirements and produce an odour assessment report to support their development application.