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Good Practice Guide for Assessing Discharges to Air from Industry

Acknowledgements

Foreword by the Ministry

1 Introduction

2 Legislative Context

3 Assessing Discharges to Air: General Considerations

4 The Assessment Process

5 Air Quality Criteria

6 Tier 1 Preliminary Assessment

7 Tier 2 Screening Assessment

8 Tier 3 Full Assessment

Appendix 1: Assessment Checklist

Appendix 2: NO to NO₂ Conversion

References

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 New Zealand regulatory framework contains the following air quality criteria:

• national environmental standards for air quality

• national ambient air quality guidelines

• objectives and policies in regional plans.

It is important to note that regional plans are statutory instruments under the RMA. If the air quality objectives in a regional plan are more stringent than the national environmental standards for air quality, then the regional plan takes precedence. For this reason it is very important to check the requirements of the relevant regional plan before undertaking any assessment of the discharges to air from industry.

New Zealand and other international air quality criteria are discussed in more detail below.

A thorough air quality assessment (some Tier 2 and all Tier 3) should address both short-term and long-term impacts. This means you will need to use air quality criteria with both short- and long-term time averages. Air quality criteria published by different agencies may overlap, complement or sometimes outright contradict each other for some pollutants and some time averages. It is very important, therefore, when selecting air quality criteria for an air quality assessment that the fundamental purpose of the standard or guideline is understood. Similarly, the application of the criteria should be considered. What may be appropriate for an existing facility operating for a five-year consent may not be appropriate for a brand new plant applying for a full 35-year term.

It should also be noted that air quality criteria may become outdated. The Ministry for the Environment website (www.mfe.govt.nz) should be checked for any updates to the national ambient air quality standards or guidelines discussed in this section.

In all cases, the assessment should explain which criteria have been selected and why. For those pollutants not covered by the criteria discussed below, or in cases where the criteria are exceeded, health risk assessment techniques should be applied.

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 micrometres in diameter (PM₁₀)

• sulphur dioxide (SO₂).

The primary purpose of the national ambient standards is to provide a guaranteed level of protection for the health of all New Zealanders.

The national ambient air quality standards, therefore, comprise acceptable concentrations for a particular time average, with a specified number of permissible exceedances each year, as summarised in Table 5.1.

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

The national 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 national 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 national ambient air quality 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 national ambient air quality standard for SO₂ does apply, in order to protect the health of any members of the public that may be exposed to emissions of SO₂.

Table 5.1: National ambient air quality standards 2004

In addition to this, when assessing the potential impacts of discharges to air from industry, careful judgement is required to determine whether people may be exposed and over what time period. General guidance is provided in Table 5.2.

Table 5.2: Location and applicability of the Standards for assessment purposes

5.1.1 Airsheds that breach the PM₁₀ standard

The regulations place constraints on resource consents depending on the pollutant, the existing air quality of an airshed relative to the national ambient air quality standards, and the date of the application. This section applies to applications for 'significant' discharges of PM₁₀ only. The term 'significant' is discussed below.

In airsheds that breach the national 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 (as PM₁₀) to air.

Readers are referred to the Updated Users Guide (Ministry for the Environment, 2005), which provides a practical interpretation of regulations 17A to 17C. Summarised, Regulation 17 means that in areas where levels of PM₁₀ exceed the standard, councils must not give consent for discharges of PM₁₀ 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 Standards. We now need to look at these paths in more detail.

Straight- and curved-line paths

The 'straight-line path' and 'curved-line path' 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 national 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 national ambient air quality standard. The formal definitions are:

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 achieve compliance with the PM₁₀ standard by 1 September 2013. They are determined by:

• the state of the air quality at the relevant date (ie, when the national 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 PM₁₀ 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 Regulations 17A 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 regulation 17

* Offsets are explained below.

It is worth noting that the curved-line path has additional conditions to the straight-line path. In particular, regulation 17B 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, refer to the Updated Users Guide (Ministry for the Environment, 2005).

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 national ambient air quality 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 occur when mitigation measures are 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 PM₁₀.

Regulation 17C was amended in July 2005 to explicitly provide for the use of offsets when considering applications for resource consents for significant discharges of PM₁₀ into airsheds where the PM₁₀ standard is already exceeded. The key provisions for offsets in regulation 17C are that they must:

• be from another source in the same airshed

• take effect within one year after the grant of the resource consent

• 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.

• Contaminant – the nature of the contaminants being 'put-in' needs to be similar to the nature of those 'taken-out'.

• Location – the emissions 'taken-out' should be in the same area as the emissions 'put-in' and not just happening 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.

• Timing – the emissions 'taken-out' should occur at the same time as the emissions 'put-in'. For example 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 Airsheds that do not breach the PM₁₀ standard

In airsheds where PM₁₀ levels do not exceed the national ambient air quality standard for PM₁₀, 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 PM₁₀ standard.

5.1.3 Carbon monoxide, nitrogen dioxide and ozone

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

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 practical advice in implementing the Standards. Without such a qualifier, very minor and even trivial discharges of CO, NOx and/or VOCs could be subject to mitigation in circumstances that did little to improve air quality. The interpretation needs to be made in the context of the specific 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 council must decline an application for a resource consent to discharge SO₂ into air if the discharge to be allowed is likely to cause the concentration of SO₂ in the airshed to breach the national ambient air quality standard for SO₂.

5.2 New Zealand air quality guidelines

The New Zealand Ambient Air Quality Guidelines were developed following a comprehensive review of international and national research, and are widely accepted among New Zealand practitioners (Ministry for the Environment, 2002). 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.

The primary purpose of the national Ambient Air Quality Guidelines is to promote sustainable management of the air resource in New Zealand.

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: National 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.

5.3 Regional plans

By 2007 all regional councils had regional air quality plans either operational or in the final stages of becoming operational. The plans reflect particular regional circumstances and may range from the very straightforward, dealing primarily with issues of open burning, to the more complex, with specific rules and plans for meeting the Standards.

It is important to understand the purpose of each regional plan when considering the application of air quality objectives (sometimes referred to as targets or goals).

From a regulatory viewpoint, regional air quality plans are statutory instruments under the RMA and have equal status with the Standards. Where concentration thresholds double up, the more stringent level applies. Thus a regional air quality objective that is more stringent than a national ambient air quality standard supersedes the national standard. The regional air quality objectives cannot, however, be more lenient than the national ambient air quality standards.

5.4 WHO air quality guidelines

In response to the increasing evidence of the health impact of air pollution, the World Health Organisation (WHO) revised its existing air quality guidelines for Europe in October 2006 and expanded them to produce the first global air quality guidelines. These guidelines are based on the latest scientific evidence and set targets for air quality to protect the large majority of individuals from the effects of air pollution on health.

The primary aim of the WHO guidelines is to provide a uniform basis for protecting public health from the effects of air pollution. They are intended for worldwide use.

Table 5.6 summarises the updated WHO air quality guideline levels. These include annual guidelines for PM2.5 and for NO₂, which are not currently covered by New Zealand standards or guidelines. The WHO 24-hour average PM2.5 guideline is consistent with the New Zealand monitoring PM2.5 guideline (Ministry for the Environment, 2002). The WHO 24-hour guideline for SO₂ is considerably more stringent than the New Zealand ambient air quality guideline.

Table 5.6: Updated WHO air quality guideline values

Notes: Items in bold are not covered by New Zealand standards or guidelines; AQG value = air quality guideline.

5.5 International air quality criteria

If there are no New Zealand ambient air quality standards or guidelines, or WHO guidelines, relevant to the chemical under assessment, a number of other international air quality criteria may be used.

As noted above, air quality criteria published by different agencies may overlap, complement or sometimes outright contradict each other for some pollutants and some time averages. It is very important, therefore, when selecting air quality criteria for an air quality assessment, for the fundamental purpose of the standard or guideline to be understood. Similarly, the application of the criteria should be considered. What may be appropriate for an existing facility operating for a five-year consent may not be appropriate for a brand new plant applying for a full 35-year term.

When using international air quality criteria, the assessment should explain which criteria have been selected and why.

The criteria discussed below are recommended because of their traceable derivation from toxicological data.³ They 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.

5.5.1 Acute exposure

For assessing short-term impacts, the California Office of Environmental Hazard Assessment acute reference exposure limits (RELs) are recommended:

www.oehha.ca.gov/air.html

The acute reference exposure limits are concentrations that are not likely to cause adverse effects in a human population, including sensitive subgroups, exposed on an intermittent basis to that concentration for one hour.

Acute reference exposure limits are intended to protect the individuals who live or work in the vicinity of emissions of these substances.

The focus of the acute reference exposure limits is generally a one-hour exposure for non-cancer health impacts.

5.5.2 Chronic exposure

For assessing long-term impacts, the US EPA inhalation reference concentrations (RfCs) and air unit risk factors are recommended:

http://www.epa.gov/iris/limits.htm

The inhalation reference concentration is an estimate of a daily exposure to the human population (including sensitive subgroups) that is likely to be without appreciable risk of deleterious effects during a lifetime. It should be noted that these concentrations are based on an assumption of lifetime exposure and may not be appropriately applied to less-than-lifetime exposure situations.

The inhalation reference concentrations can be used to estimate a level of environmental exposure at or below which no adverse effect is expected to occur.

The inhalation reference concentrations are 24-hour averages and focus on non-carcinogenic health impacts.

The US EPA air unit risk factors are quantitative estimates of the upper-bound excess lifetime cancer risk estimated to result from continuous exposure to an agent at a concentration of 1 µg/m³ in air. The interpretation of unit risk would be as follows:

If unit risk = 2 x 10-6 per µg/m³ then two excess cancer cases (upper-bound estimate) are expected to develop per 1,000,000 people if exposed daily for a lifetime to 1 µg of the chemical in 1 cubic metre of air.

Quantitative estimates of risk factors for carcinogens are provided in the US EPA Integrated Risk Information System (IRIS) database, referred to in the above web address. As with the inhalation concentrations, the unit risk factors are based on an assumption of lifetime exposure and may not be appropriately applied to less-than-lifetime exposure situations.

In New Zealand, an acceptable environmental risk for exposure to environmental pollution of 1 in 100,000 has been adopted by the Ministry for the Environment in a range of guidelines for the management of contaminated land, most recently in the Guidelines for Assessing and Managing Petroleum Hydrocarbon Contaminated Sites in New Zealand (Ministry for the Environment, 1999b). It is recommended that a similar level of risk be used when assessing discharges to air from industry.

Alternatively, the California Office of Environmental Hazard Assessment chronic reference exposure limits (RELs) may be used. A chronic reference exposure level is an airborne level that would pose no significant health risk to individuals indefinitely exposed to that level. RELs are based solely on health considerations, and are developed from the best available data in the scientific literature.

www.oehha.ca.gov/air.html

Chronic reference exposure limits are annual averages and focus on non-carcinogenic health impacts.

5.6 Workplace exposure standards

For some contaminants, and 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 amended for use as assessment criteria. The workplace exposure standards cover many of the chemicals that might be discharged, but they are set for protecting healthy people in a workplace setting (ie, 40-hour working week). In order to be used to protect more sensitive members of the community (the very young, the elderly, those whose health is already compromised) these standards should be divided by a safety factor for assessment over an eight-hour exposure period.

Historically a range of factors has been used. The Auckland Regional Council approach is recommended here (Auckland Regional Council, 2002):

• WES TWA divided by 50 for low and moderately toxic hazardous air pollutants, or

• WES TWA divided by 100 for highly toxic bioaccumulative or carcinogenic hazardous air pollutants.

This is based on division by 42 (rounded to 50). The factor of 42 is used to convert the eight-hour WES TWA into a 24-hour average over a whole week of discharges and then adding a further safety factor of 10 to account for protecting more sensitive portions of the population than healthy workers. The 100 factor has been derived by the same method, except that a safety factor of 20 has been used to account for more toxic hazardous air pollutants or more long-term chronic effects.

These WES TWA criteria should be compared with either a three-minute (Ausplume) or a one-hour average (all other models) depending on the air dispersion model used.

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