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Good Practice Guide on Assessing Discharges to Air from Industry

Foreword by the Ministry

Acknowledgements

1 Introduction

2 Legislative Context

3 Assessing Discharges to Air from Industry

4 The Assessment Process

5 Air Quality Criteria

6 Tier 1 Preliminary Assessment

7 Tier 2 Screening Assessment Process

8 Tier 3 Full Assessment Process

References

Appendix 1: Assessment Checklist

5 Air Quality Criteria

The extent to which the impacts on air quality caused by an industrial development are considered acceptable is judged by the use of air quality criteria. The following air quality criteria are used to assess discharges to air from industry in New Zealand: [Ministry for the Environment website http://www.mfe.govt.nz/publications/air/ should be checked for the publication of any update to the air quality standards or guidelines summarised in sections 6.1.1 and 6.1.2.]

• New Zealand ambient air quality standards (Schedule 1 of the Standards)
• New Zealand Ambient Air Quality Guidelines (Ministry for the Environment, 2002).

For those pollutants not covered by the Standards or the Ambient Air Quality Guidelines, approaches to derive air quality criteria are given in section 6. Health risk assessment techniques should be applied when international air quality criteria are not available (see section 3).

Note that consenting authorities can specify stricter (but not more lenient) targets in their regional plans, and some do for some contaminants. For this reason, it is important to check the requirements of the relevant regional plan before undertaking any assessment of the discharges to air from industry.

5.1 National Environmental Standards for Air Quality

Schedule 1 of the Standards provides ambient concentration limits for the following pollutants:

• carbon monoxide (CO)
• nitrogen dioxide (NO₂)
• ozone (O₃)
• fine particulate matter that is less than 10 micrometers in diameter (PM₁₀)
• sulphur dioxide (SO₂).

These ambient air quality standards comprise acceptable concentrations for a particular time average, with a specified number of permissible exceedances each year, as summarised in Table 5-1.

Application of the ambient air quality standards is provided in the Updated Users' Guide (Ministry for the Environment, 2005b). A number of key issues relevant to the assessment of discharges from industry are discussed here.

The ambient air quality standards apply in the open air everywhere people may be exposed. This includes roadside verges, residential areas, central business districts, parks and beaches. Areas that are not in the open air and where the Standards do not apply include:

• inside a house
• inside tunnels
• inside vehicles.

However, the ambient air quality standards are not applicable on sites to which resource consents apply. For example, Acme Fertiliser may operate a large factory with emission limits specified in their resource consent for discharges of SO₂. The ambient standard for SO₂ does not apply within the area to which Acme's resource consent applies (ie, the site boundary), because the workers on the Acme site are protected under health and safety legislation. Off-site next door at the Green Fingers Garden Centre, however, the ambient standard for SO₂ does apply, in order to protect the health of any public that may be exposed to emissions of SO₂.

Table 5-1: Ambient air quality standards 2005

When assessing the potential impacts of discharges to air from industry, careful judgement is required to determine whether people may be exposed. General guidance is provided in Table 5-2.

Table 5-2: Locations where standards should and should not apply for assessment purposes

The regulations place constraints on resource consents depending on the pollutant, the existing air quality of an airshed relative to the ambient air quality standards, and the date of the application. The following sections describe the requirements for resource consents to discharge contaminants to air.

5.1.1 Fine particulate (PM₁₀) in airsheds that breach the standard

In airsheds that breach the ambient standard for PM₁₀ before 1 September 2013, regulations 17A to 17C apply if the discharge to be permitted by the resource consent is likely to significantly increase the concentration of PM₁₀ in the airshed. After 1 September 2013, in airsheds where PM₁₀ levels exceed the standard, councils cannot give consent to any discharges of fine particles to air.

Readers are referred to the Updated Users Guide (Ministry for the Environment, 2005b) which provides a practical interpretation of regulations 17A to 17C. Summarised, Regulation 17 means that in areas where levels of fine particles exceed the standard, councils must not give consent for discharges of fine particles to air if the discharges are likely to cause the airshed to be significantly above the 'straight-line path' (or 'curved-line path') to meeting the standard. We now need to look at these paths in more detail.

Straight and curved-line paths

The 'straight-line path' and 'curved-line path' basically refer to lines on a graph that plots PM₁₀ over time. The form of the path is determined by the state of the air quality when the ambient air quality standards came into force on 1 September 2005 and the rate at which things must improve to achieve compliance by 1 September 2013. According to the Regulations, a straight-line path or curved-line path applies to any airshed in a region in which the concentration of PM₁₀ breaches the standard. The formal definitions run as follows.

curved-line path means a curved line that:

(a) starts on the y axis of a graph at a point representing, as at 1 September 2005 or the date that the plan is publicly notified (whichever is the later), the concentration of PM₁₀ in the airshed; and

(b) ends on the x axis of the graph at a point representing as at 1 September 2013, the ambient air quality standard for PM₁₀ in the airshed

regional plan includes a proposed regional plan

relevant date means -

(a) in the case of an airshed that is the region of a regional council, 1 September 2005;

(b) in the case of an airshed that is part of the region of a regional council, the date of the notice in the Gazette that specifies the part to be a separate airshed

straight-line path means a straight line that:

(a) starts on the y axis of a graph at a point representing, as at the relevant date, the extent to which the concentration of PM₁₀ in the airshed breaches its ambient air quality standard; and

(b) ends on the x axis of the graph at a point representing, as at 1 September 2013, the ambient air quality standard for PM₁₀ in the airshed.

For the purposes of deciding resource consents, the straight-line path and curved-line path are projections of how the regional council will attain compliance with the fine particle standard by 1 September 2013. They are determined by two things:

• the state of the air quality at the relevant date (ie, when the ambient air quality standards came into force on 1 September 2005 or the gazettal date of their airshed)
• the rate at which air quality must improve in order to achieve compliance by 1 September 2013.

Although straight-line paths are not required to be gazetted, they are likely to be published by regional councils to indicate the effectiveness of various air quality management strategies to meet the fine particle standard. In addition to these projected paths to compliance, as time passes, councils will be able to plot their observed path to compliance (ie, a plot of concentration versus time).

Interpretation of sections 17 to 17C

Taking into account the airshed status, the significance of the discharge, the approach to compliance (projected) and the status of compliance (observed), the application for resource consent may then be decided, as shown in Table 5-3.

Table 5-3: Resource consents for significant discharges of PM₁₀ under section 17

It is worth noting that the curved-line path has additional conditions to the straight-line path. In particular, regulation 17 specifies that a curved-line path must be contained within a regional plan and further that the regional plan have rules restricting the granting of resource consents. For more information readers are referred to the Updated Users' Guide (Ministry for the Environment, 2005b).

Significance

No specific guidance can be offered for what constitutes a 'significant' discharge because it depends on a multitude of factors. However, some issues to consider when determining whether a discharge is significant include:

• the predicted impact of the proposal
• the conservatism in predicting impacts:
  • is it likely that breaches will actually occur?
  • if so, under what conditions will breaches occur, and how often?
• the sensitivity of the receiving environment
• the accuracy/reliability of the assessment process
• the extent to which the standard is already breached
• for major projects, the valuation/cost of health impacts.

Because of these various factors, what constitutes 'significant' will need to be determined by the normal RMA process on a case-by-case basis.

Offsets

'Offsets' are mitigation measures included in a proposal to offset predicted impacts, so that emissions from the new activity are offset by emission reductions elsewhere in the airshed. A straightforward example would be an industrial development helping to reduce emissions from a hospital boiler located nearby: the reduced fine particle emissions from the hospital boiler offset the proposed industrial discharges of fine particles.

Regulation 17 was amended in July 2005 to explicitly provide for the use of offsets when considering applications for resource consents for significant discharges of fine particles into airsheds where the standard is exceeded. The key provisions for offsets in regulation 17C are:

• they must be from another source in the same airshed
• they must take effect within one year after the grant of the resource consent
• they must be effective for the duration of the consent.

The amount of the offset is dictated by the observed path to compliance, as follows:

• if the airshed is on or below the path to compliance, then the offset must be at least equal to the change in concentrations caused by the resource consent; or
• if the airshed is above the path to compliance, then the reduction must be at least equal to the amount of discharge permitted by the resource consent.

Regulation 17C does not make explicit provision for consideration of the following.

• The nature of the contaminants being 'put-in' needs to be similar to those 'taken-out'.
• The spatial and temporal improvement from the 'take-out' of emissions giving benefits in the area impacted by the 'put-in' at the relevant time (ie, location and duration of emissions must also be considered) - other than being in the same airshed. For example, it would not be sufficient to 'take-out' emissions from a facility in Manukau to offset emissions to be 'put-in' by a facility on the North Shore of Auckland, even though both areas are within the same airshed. Similarly, it would not be sufficient to 'take-out' emissions from a facility that discharges all year round to offset emissions that discharge only once a year, even though both discharges are the same mass amount.

It is, however, sensible to take such factors into consideration when considering applications involving offsets. An emissions offset may be carried out by any party.

5.1.2 Fine particulate (PM₁₀) in airsheds that do not breach the standard

In airsheds where PM₁₀ levels do not exceed the standard, either before or after 1 September 2013, councils must not give consent for discharges of PM₁₀ to air if the discharges are likely to cause the airshed to exceed the standard.

5.1.3 Carbon monoxide, nitrogen dioxide and ozone

For carbon monoxide (CO), oxides of nitrogen (NO_x) and volatile organic compounds (VOCs), resource consents must be declined where the discharge is likely to cause a breach of the standard for CO, NO₂ or ozone, and the discharge is a principal source (of CO, NO_x or VOC).

Principal source

As with the concept of 'significance' in the regulations, there is no specific guidance on what constitutes a 'principal source'. The wording is designed to offer some elements of practicality in implementing the Standards. Without such a qualifier, very minor and even trivial discharges of CO, NO_x and/or VOC could be subject to mitigation in circumstances that did little to improve air quality. The interpretation needs to be taken in the context of the issues within the airshed, particularly the extent of any exceedances, and the contribution of the source to those exceedances.

5.1.4 Sulphur dioxide

For SO₂, a consent authority must decline an application for a resource consent to discharge SO₂ into air if the discharge to be permitted is likely to cause the concentration of SO₂ in the airshed to breach its ambient air quality standard.

5.2 Ambient air quality guidelines

The ambient air quality standards are based on the existing Ambient Air Quality Guidelines (Ministry for the Environment, 2002). These guidelines were developed following a comprehensive review of international and national research, and are widely accepted among New Zealand practitioners. They were published by the Ministry for the Environment as guidance under the RMA, and provide the minimum requirements that outdoor air quality should meet in order to protect human health and the environment.

Guideline levels for pollutants (and averaging periods) not covered by the Standards still apply. The Standards replace any previous guideline levels for that particular pollutant and averaging period. In addition to the human health-based guidelines presented in Table 5-4, guidelines for ecosystem protection are provided for sulphur dioxide, sulphate particulate, nitrogen dioxide, ammonia, ozone and fluoride, as shown in Table 5-5.

Table 5-4: Ambient air quality guidelines, 2002

Table 5-5: Critical levels for protecting ecosystems

Notes: Critical levels for NO₂ assume that either O₃ or SO₂ are also present at near guideline levels. Critical levels for O₃ are expressed as a cumulative exposure over a concentration threshold referred to as AOT40 values (accumulative exposure over a threshold of 85.6 µg/m³, at 0°C), calculated as the sum of the difference between hourly ambient O₃ concentrations and 85.6 µg/m³, when O₃ concentrations exceed 85.6 µg/m³). O₃ is only measured during daylight hours with a clear global radiation of 50 Wm-2 or greater.

vpd = vapour pressure deficit.

5.2.1 Non-criteria air pollutants

Australia's National Environmental Protection Council recently released the National Environmental Protection Measure (Air Toxics) (Australian NEPC, 2004). This puts in place a monitoring framework for five pollutants. It includes toluene and xylene, which are not covered by the New Zealand Standards and guidelines. Schedule 3 of the measure provides monitoring assessment levels which, if exceeded, provide a prompt for further investigation. The NEPC criteria should be applied for assessments of toluene and xylene.

For other pollutants not included in either the Standards or the Ambient Air Quality Guidelines (Ministry for the Environment, 2002), there are a number of extensive sets of assessment criteria that may be referred to, including:

• Texas − effects screening levels (Texas Commission on Environmental Quality, 2003)
• Washington − ambient source impact levels (Washington Department of Ecology, 1998)
• Ontario - point of impingement standards (Ontario Ministry for the Environment, 2001).

It is important to note that these criteria have been developed for different modelling averaging times, with the Ontario point of impingement values using 30-minute averages, the Washington ambient source impact levels using one-hour averages, and the Texas effects screening levels using either one-hour or annual averages. The aim of the particular guideline should also be considered (eg, whether it is the prevention of health impacts, odour nuisance, etc.). In general, the criteria taken from these sources should be selected based on the exposure characteristics for the development of interest and the potential effect in the receiving environment.

The criteria should be applied primarily as screening criteria. If the modelling/monitoring results are well within the assessment criteria, then the effects on public health and the environment should be minor. However, if the results exceed the criteria, then a full health risk assessment is required (see section 8.5) and/or action will be needed to mitigate the emissions before consent is granted.

In the air impact assessment, the range of criteria considered should be identified and a rationale for the criteria selected for an assessment provided.

Other Australian guidelines have been considered in the preparation of these guidelines, but they are not recommended for use. [Victoria, in its State Environment Protection Policy (Air Quality Management), revised 2001, has an extended list of pollutant design criteria within Schedule A. Within Schedule A, there are three classes:

• class I covers pollutants covered by New Zealand standards and guidelines
• class II covers many non-criteria pollutants
• class III covers carcinogens, mutagens, teratogens and highly toxic compounds.

The class II design criteria were derived from threshold limit values from the US ACGIH (pre-dating 1988), with the design criterion equalling the Threshold Limit Value (TLV) divided by 30. These values have not always been updated as the source occupational health values are revised. Class III provides three-minute time average criteria for carcinogens by taking pre-1988 TLVs divided by 300. Carcinogenic effects are usually considered over annual or lifetime exposure. The use of these short-term criteria is considered to lag behind the developing knowledge and approaches for establishing criteria for air quality protection.]

Workplace Exposure Standards

For some contaminants, in the absence of any other guidance, the Department of Labour Occupational Health and Safety, Workplace Exposure Standards, Time Weighted Average (OSH WES TWA) can be used as assessment criteria. These cover many of the chemicals that might be discharged, but they are set for protecting healthy people in a workplace setting. In order to be used to protect more sensitive members of the community (the very young, the elderly, those health compromised), these standards should be divided by 40 and then assessed over an eight-hour exposure period. For instance, the WES for arsenic is 0.05mg m^-3. Divided by 40 gives an assessment level of 1.25µg m^-3. A discharge should not result in a peak concentration above 1.25µg m^-3 averaged over eight hours.

The use of the factor of 40 here is informal. In the past, a factor of 30 had been used. For some applications there is support for applying a factor of 100, or alternatively allowing for a safety margin of 10, which equates to applying a factor of 400. Some regional councils have specific guidance, and this should be followed where available. When the use of the method is necessitated, judgement must be used as to the appropriate factor. It should not be less than 40, but may need to be greater for highly sensitive receiving environments.

Note that in some cases a specific ambient air quality criterion has been established and this should be used in preference to the OSH WES. In the example used for arsenic, the ambient air quality guideline (from Table 5-4) is for an annual average at 0.0055µg m^-3. This is formulated as an annual average to account for longer-term effects. In general, both the short-term WES figures and the long-term ones should be met.