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3 What to Monitor? – Choosing Contaminants

This chapter describes the ambient air quality standards and guidelines and discusses how air quality monitoring fits into the regulatory framework.

New Zealand has national environmental standards for five air contaminants as well as 15 ambient air quality guidelines. Guidelines that apply over the same averaging period for a particular contaminant have been effectively superseded by the standards. This is not simply a change in designation from guideline to standard. The following summarises the basic differences between standards and guidelines.

  • Ambient air quality standards are concentration limits set to protect New Zealanders’ health. They have the force of regulation under the Resource Management Regulations 2004 and have mandated monitoring methods and reporting requirements. Some ambient air quality standards incorporate a specified number of allowable exceedences in any 12‑month period.

  • Ambient air quality guidelines are concentration limits recommended to protect human health and the environment under the Resource Management Act 1991 (RMA). They may be incorporated into regional plans as objectives or targets. The ambient air quality guidelines do not specify allowable exceedences.

Note: Guidelines for contaminants not covered by standards still apply. Guidelines should be followed as closely as possible for the sake of good practice and national consistency.

From a regulatory viewpoint, regional air quality plans are statutory instruments under the RMA and have equal status with the standards. If the air quality objectives in a regional air quality plan are more stringent than the NES for air quality, then the regional plan takes precedence. Regional air quality objectives, however, cannot be more lenient than the NES for air quality (Ministry for the Environment, 2008).

3.1 Monitoring for standards and guidelines

The term ‘airshed’ as used in the regulations is more akin to an ‘air quality management area’ rather than being a strictly science-based concept of an airshed (although in many instances the two are equivalent). These airsheds were designated through recommendations made by regional councils and unitary authorities to the Minister for the Environment. They extend upwards from ground level, including coastal marine areas, and have no specified upper limit. In most cases they represent areas that are known, or likely, to exceed the fine particle ambient standard. The exception to this is the Marsden Point airshed, which is based on its likely or known breaches of the sulphur dioxide standard.

3.1.1 National environmental standards (NES) for ambient air quality

The NES for air quality apply at any place in the open air where a person might reasonably be expected to be exposed to the contaminant over the relevant averaging period. This does not include tunnels, indoor areas or outdoor workplace sites, whose emissions are covered by Occupational Safety and Health regulations.

The standards are based on the ‘no observable adverse effect’ level or ‘lowest observable adverse effect’ level in relation to human health. Where epidemiological studies and international guidelines have been unable to determine such a threshold, a judgement has been made as to what constitutes an ‘acceptable’ health risk.

Table 1 shows the airborne contaminants included in the NES for air quality which are considered to be of greatest concern and most likely to exist in New Zealand.

Table 1: National environmental standards for ambient air quality

Contaminant Threshold concentration Time average Permissible excess per year
Carbon monoxide (CO) 10 mg/m3 Running 8-hour mean 1
Nitrogen dioxide (NO2) 200 µg/m3 1-hour mean 9
Ozone (O3) 150 µg/m3 1-hour mean 0
PM10 (fine particles) 50 µg/m3 24-hour mean 1
Sulphur dioxide (SO2) 350 µg/m3
570 µg/m3
1-hour mean
1-hour mean

The ambient standards came into effect on 1 September 2005. The standards include permissible exceedences for CO, NO2, PM10 and the 350 µg/m3 SO2 standards. There are no permitted exceedences for O3 or the 570 µg/m3 SO2 standards.

Certain human activities are associated with the emission of particular groups of contaminants. Emissions from domestic fires monitored at a neighbourhood site may require the monitoring of CO in addition to PM10. In areas where high sulphur content solid fuel is burnt, SO2 may be another contaminant to monitor.

Refer to appendix A for Schedule 1 of the NES for air quality.

3.1.2 Ambient air quality guidelines

The Ambient Air Quality Guidelines (AAQG) are health-based guidelines that set the minimum requirements that outdoor air quality should meet in order to protect human health and the environment.

Table 2 outlines the existing 15 ambient air quality guidelines for a range of contaminants. This includes guidelines with different values and time averages to the standards for carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM10), and sulphur dioxide (SO2). These guidelines have not been superseded by standards because they measure a different time average, and therefore provide an indication of human exposure on a different time scale. It is important to assess air quality in terms of both short-term (eg, peak) exposure and long-term exposure (eg, annual averages).

Table 2: Ambient air quality guidelines (2002)

Contaminant Guideline valuea Time average
Carbon monoxide 30 mg/m3 1-hour mean
Nitrogen dioxide 100 µg/m3 24-hour mean
Ozone 100 µg/m3 8-hour mean
PM10 20 µg/m3 Annual mean
Sulphur dioxideb 120 µg/m3 24-hour mean
Hydrogen sulphidec 7 µg/m3 1-hour mean
Leadd 0.2 µg/m3 3-month rolling mean (calculated monthly)
Benzene (2002)
Benzene (2010)
10 µg/m3
3.6 µg/m3
Annual mean
Annual mean
1,3-butadiene 2.4 µg/m3 Annual mean
Formaldehyde 100 µg/m3 30-minute mean
Acetaldehyde 30 µg/m3 Annual mean
Benzo(a)pyrene 0.0003 µg/m3 Annual mean
Mercury (inorganic)d
Mercury (organic)
0.33 µg/ m3
0.13 µg/ m3
Annual mean
Annual mean
Chromium IV d
Chromium metal and chromium III d
0.0011 µg/m3
0.11 µg/m3
Annual mean
Annual mean

Arsenic (inorganic)d

0.0055 µg/m3
0.055 µg/m3

Annual mean
Annual mean


a All values apply to the gas measured at standard conditions of temperature (0oC) and pressure (1 atmosphere).

b The sulphur dioxide guideline values do not apply to sulphur acid mist.

c The hydrogen sulphide value is based on odour nuisance and may be unsuitable for use in geothermal areas.

d The guideline values for metals are for inhalation exposure only; they do not include exposure from other routes such as ingestion. These other routes should be considered in assessments, where appropriate.

Monitoring PM2.5 is recommended if resources are available (see section 5, Particulate Monitoring, for further details). Results may be compared with the World Health Organization’s annual PM2.5 guideline of 10 µg/m3 (World Health Organization, 2006) or the monitoring guideline of 25 µg/m3 (24-hour average) stated in the AAQG.

Additional guidance and information on the NES for air quality and the AAQG can also be found in the following documents.

  • The Updated User’s Guide to Resource Management (National Environmental Standards Relating to Certain Air Pollutants, Dioxins and Other Toxics) Regulations 2004 (Including Amendments 2005) (Ministry for the Environment, 2005) is aimed at practitioners in local government implementing the first suite of national environmental standards. Chapter 3 of the User’s Guide deals with ambient air quality standards from an air quality management and consent perspective.

  • Ambient Air Quality Guidelines (Ministry for the Environment, 2002) pre-dates the introduction of the NES for air quality and includes guideline values for contaminants not covered by the standards. Chapter 2 contains useful information on health effects and sources of airborne contaminants. Although the NES for air quality has mandatory considerations for the processing of resource consents, chapter 3 of the guidelines still provides useful general guidance on regional air quality management.

3.2 Meteorological monitoring

Weather has a profound influence on contaminant dispersion and concentrations. For example, meteorological effects such as temperature inversions can dramatically increase contaminant levels. It would not be possible to gain a clear picture of the air quality in an area without meteorological monitoring. Good-quality meteorological data is necessary, and may require a number of stations depending on topography. Basic meteorological monitoring at some air quality monitoring sites may prove very useful, especially when trying to assess the validity of data. Meteorological data is also critical in the use of dispersion modelling.

A detailed set of guidelines for meteorological monitoring has been prepared by the United States Environmental Protection Agency (USEPA, 2000). The Australian standard, AS 2923:1987, Measurement of horizontal wind, provides guidance on the measurement of wind speed and direction. Additional guidance can also be sourced from the Guide to Meteorological Instruments and Methods of Observation (World Meteorological Organization, 1996).