Proposed approach for management of chronic odour exposures in New Zealand


Author: Roger Cudmore – RMLA Air Quality Knowledge Hub Leader

In this article, a case is put forward for refining the management of chronic odour exposure effects under the Resource Management Act (RMA).

There is widespread acceptance, that chronic (long term) exposures to sub-objectionable levels of environmental odour can manifest in significant stress and annoyance within a community. This type of exposure is different from the occurrence of acute odour exposure episodes (occurring on a specific day), which are objectionable or offensive to an extent that causes an adverse effect.

The occurrence of these short-term events has been the basis for past prosecution actions against industrial/commercial operations under the RMA and its predecessor, the Town and Country Planning Act 1977. In some decisions, the Environment Court has referred to chronic odour effects and subsequently imposed restrictions on a commercial operation for causing what amounts to significant chronic odour effects.

While there are no clear examples where chronic odour exposures have themselves, led to prosecution actions, it is argued that such exposures, when causing significant effects, should not be subject to the objectionable or offensive standard. Instead, objective criteria should apply to justify the need, or otherwise for further controls at a site.


In the late 1990’s the concept of chronic and acute odour exposures was coined, and these terms are widely accepted for describing the two extremes of odour exposure that can arise from an industrial/commercial facility. The first relates to the stress and annoyance incurred by people, which can develop over time due to repeated exposures to odour (chronic effects). Acute odour effects relate to specific episodes of exposure, which can be deemed objectionable or offensive.

When assessing odour effects from proposed or existing facilities, it accepted practice to consider the potential effects on a community arising from both chronic and acute odour exposures. This is embodied by the current Ministry for Environment good practice guideline for the assessment of odour effects.

In practice, acute odour events (when these are objectionable) usually arise as a consequence of a loss of process control, failure of equipment, or procedure, or operating outside of consent limits. By comparison, chronic odour exposure effects are typically related to normal operating conditions that are within consented operating limits.

The onset of significant chronic odour effects can take a time to develop (months to years) and without the knowledge, or clear understanding by a facility’s managers, owners that they may be responsible, in retrospect, for causing an objectionable or offensive odour. By comparison, acute odour exposures, which are objectionable, are far more associated with culpability, management failures and knowledge of the potential impact on the surrounding community.

Current Issues

The occurrence of chronic exposures to sub-objectionable odour events over the long-term is (from the author’s experience) the most prevalent cause of complaints regarding environment odours. The situations where industrial facilities discharge strong intensity odours that are objectionable is relatively rare.

As such officers typically find sub-objectionable levels of odour during field surveys. Confirmation of objectionable odour is more often a result of an officer having to surmise the likely impact of repeated exposures over time, to the odour observed during their investigation. This can result in sub-objectionable levels of repeated odour being determined as objectionable or offensive.

It is clear, that chronic odour exposures due to facilities can, over time, lead to excessive annoyance and community stress and high complaint levels. However, the validity in categorising these scenarios as potentially objectionable or offensive is questionable.

Where the long-term exposure to sub-objectionable odours leads to adverse effects (community annoyance) – this may well justify the imposition of increased controls on odour discharges from a facility. But excluding such effects from the category of objectionable or offensive would avoid the unnecessary prospect of prosecution actions, excepting where facilities do not comply with Court directions.

One of the obstacles to decoupling chronic odour exposure effects from the objectionable or offensive odour standard is the lack of numeric criteria for assessing chronic odour exposure effects. In Europe, this has been provided for via population annoyance targets (% at least annoyed), odour hours criteria, as well as odour modelling criteria. There is a lack of such nationally accepted criteria in New Zealand.

The MfE odour guide (published in 2016) currently has no criteria for the assessment of chronic odour exposure information apart from the use of odour modelling criteria – which has limited applications. While the guide recommends a range of field and community survey methods as key assessment tools (and especially chronic odour exposure levels), it provides little or no guidance on the evaluation of resultant information.

The current guide has also removed the previous criterion of 20%-at-least annoyed for analysis of community odour annoyance survey data. This removed an important benchmark for allowable levels of chronic odour effects.

In response, odour hour criteria (% of hours) have been derived in recent years to assist in the assessment of odour survey data (community and field surveys) and for the assessment of consent applications. On occasions, odour hour criteria have been presented to Court, and also to numerous consent hearing panels. These have been developed from similar “odour hour” criteria that are adopted within Europe.


It proposed that, in situations where chronic exposure to predominantly sub-objectionable odours (arising from industrial/commercial discharges to atmosphere) causes significant adverse effects within a community, that these accumulated exposures are not categorised as an objectionable or offensive odour. Instead, only specific episodes of acute odour exposure would be subject to the objectionable or offensive standard under New Zealand’s environmental legislation.

Further to the above, decisions from the Courts or hearing panels which find that chronic odour exposures are likely to have caused, or could cause, significant community annoyance, could conclude significant adverse odour annoyance effects.  Such decisions should be linked to accepted long-term odour exposure criteria (such as % odour hours).

However, decisions that find objectionable or offensive odour would be restricted to the consideration of acute odour exposure episodes. These recommendations are provided to encourage more sustainable outcomes for our industry and communities which they operate within.