View all publications

National environmental indicator

See chapter 1, ‘Environmental reporting’, for more information on the core national environmental indicators and how they are used.

The national environmental indicator for air provides information on air quality in managed airsheds (also known as gazetted airsheds – see box ‘Gazetted airsheds’). To report on the indicator, regional councils and unitary authorities measure levels of PM10 particulates, nitrogen dioxide, carbon monoxide, sulphur dioxide, and ground-level ozone. The indicator compares air quality with New Zealand’s national environmental standards (NESs) for ambient air quality. In this chapter, we refer to the NESs for ambient air quality as ‘ambient standards’.

Gazetted airsheds

Regional councils and unitary authorities have identified and made public (through the New Zealand Gazette) populated areas that are known, or have the potential, to have levels of pollutants higher than permitted by the ambient standards. These areas are referred to as gazetted airsheds.

At the time of publication, 69 airsheds had been gazetted. Of these, 68 were gazetted because of their potential to breach the ambient standard for PM10 particulates. The other airshed is at Marsden Point, Northland. It has the potential to breach the ambient standard for sulphur dioxide.

During the winter of 2006, air quality failed to meet the ambient standard for PM10 particulates at 28 airsheds. Most of these events occurred during winter temperature inversions.

National environmental standards for ambient air quality

In September 2005, five ambient standards for air quality came into effect. These are part of 14 national environmental standards introduced through the Resource Management (National Environmental Standards Relating to Certain Air Pollutants, Dioxins, and Other Toxics) Regulations 2004 (made under the Resource Management Act 1991).

The ambient standards set maximum thresholds for five commonly recognised, or key, air pollutants. These are PM10 particulates, nitrogen dioxide, carbon monoxide, sulphur dioxide, and ground-level ozone. Although the effects of air pollution on the natural environment are recognised, New Zealand’s ambient standards are measured primarily against human health thresholds.

Reporting on air quality

The Regulations require regional councils and unitary authorities to measure and publicly report on air quality whenever pollution in a gazetted airshed exceeds limits set by the ambient standards. Regional councils and unitary authorities have identified airsheds where PM10 particulates are known or suspected to be of concern. PM10 particulate levels in these airsheds are required to comply with the ambient standard for that pollutant by 2013.

In addition to ambient standards, the Regulations introduced other measures to improve air quality, including prohibition and design standards as discussed below.

Prohibition standards

Certain activities such as burning tyres, bitumen, coated wire, and oil in the open air have been prohibited. The standards also prohibited the use of incinerators at schools and health-care institutions unless authorised by resource consent, and prohibited the use of new high-temperature hazardous waste incinerators.

Design standard for wood burners

A design standard for new wood burners installed after September 2005 has been introduced to ensure the reduction of particulate emissions and provide better heat efficiency than that achieved by older wood burners. Although the wood burner standard limits emissions of particulates, it has the additional benefit of controlling emissions of other harmful pollutants such as carbon monoxide, volatile organic compounds (VOCs), hydrocarbons, and dioxins (see box ‘What are dioxins?’).

What are dioxins?

Dioxins are highly toxic compounds (known as persistent organochlorines) that build up in the fatty tissue of animals and humans. They are known to affect the immune, nervous, and reproductive systems, and have been linked to cancer. The World Health Organization has determined that no safe levels exist for exposure to dioxins.

Dioxins are formed as the result of chemical processes. Discharges of dioxins to the air mainly come from burning waste, fuel combustion, and industrial activities such as metal smelting.

Dioxins released into the air move with air currents but eventually settle on the land or water. Dioxins can enter the food chain when grazing animals or fish ingest them, and they are stored in their fatty tissue. Over 90 per cent of people’s exposure to dioxins in New Zealand is thought to come from their eating meat, fish, and dairy products.

Background levels of dioxins in New Zealand are generally low compared with levels in many northern hemisphere countries (Ministry for the Environment, 2001). Historically, activities such as the manufacture of 2,4,5-T (for example, in New Plymouth) and some timber-tanalising processes were significant sources of dioxin. However, dioxin levels have fallen over past decades as New Zealand has moved away from activities that generate dioxins (Ministry for the Environment, 2006b).

A study undertaken to determine the concentration of persistent organochlorine compounds (including dioxins) in the breast milk of New Zealand women showed that levels of these pollutants decreased by about 70 per cent between 1988 and 1998 (Bates et al, 2001).

In line with our international commitments under the 2001 Stockholm Convention, a series of measures have been taken to reduce the release of dioxins through the New Zealand Dioxin Action Plan agreed in 2002 (Ministry for the Environment, 2006b).

In addition, seven national environmental standards were introduced from 2004 to ban certain dioxin-producing activities, such as burning waste in school and hospital incinerators, burning tyres or coated wire in the open, and operating new high-temperature hazardous waste incinerators.

Limits set by the five ambient standards

The limits set by the ambient standards are summarised in Table 7.1.

Table 7.1: New Zealand’s national environmental standards for ambient air quality

Pollutant Concentration limit Number of occasions concentration limit may be exceeded


50 µg/m3 (measured as a 24-hour average)

One 24-hour period in a 12-month period

Nitrogen dioxide

200 µg/m3 (measured as a 1-hour average)

Nine hours in a 12-month period

Carbon monoxide

10 mg/m3 (measured as a running 8-hour average)

One 8-hour period in a 12-month period

Sulphur dioxide

350 µg/m3 (measured as a 1-hour average)

570µg/m3 (measured as a 1-hour average)

Nine hours in a 12-month period

Not to be exceeded at any time


150 µg/m3 (measured as a 1-hour average)

Not to be exceeded at any time


µg/m3 = micrograms per cubic metre.

Source: Resource Management (National Environmental Standards Relating to Certain Air Pollutants, Dioxins, and Other Toxics) Regulations 2004.

The indicator discussed in this chapter measures air quality in terms of the number of exceedences, peak levels, and annual averages for each pollutant.

Exceedences are the number of times a pollutant fails to meet an ambient standard. Each ambient standard provides a permissible number of occasions in which the standard may be exceeded in any 12-month period. When more exceedences occur than are permitted by the Regulations, the air quality is described as breaching the standard. For example, the Te Kūiti airshed exceeded the ambient standard for PM10 particulates twice during 2005, constituting one breach of the ambient standard.

Peak levels indicate the severity of pollution events (that is, the maximum level) over a 12-month period, while exceedences indicate the frequency of pollution events over a reporting period. For example, the highest 24-hour concentration for PM10 particulates in the Te Kūiti airshed during 2005 was 54 micrograms per cubic metre.

Annual averages are the average concentration of the pollutant over a year. Annual averages are useful for trend analysis, because data is averaged over a year, so is less affected by unusual, or atypical, values. Annual averages can also indicate the long-term exposure of New Zealanders to pollutants. The ambient guidelines recommend an annual average concentration limit of 20 micrograms per cubic metre for PM10 particulates.

Pollutants measured by the national environmental indicator for air

PM10 particulates

PM10 particulates are airborne particles that are smaller than 10 microns in diameter (about a fifth of the thickness of a human hair). These particles are described as ‘thoracic’ because they are small enough to penetrate deeply into the human lung. They have a broad range of negative health effects on people’s respiratory and cardiovascular systems.

Particulates are produced by the combustion of wood (see Figure 7.2a) and fossil fuels (mostly by home heating and road traffic), as well as various industrial processes.

Secondary particulates also form through atmospheric reactions of sulphur dioxide, oxides of nitrogen, and certain organic compounds. Particulates do not come just from human sources. Natural sources such as dust, pollen (see Figure 7.2b), sea salt (see Figure 7.2c), and soil particles also contribute to PM10 particulate levels in the environment. Though the ambient standards set acceptable levels of PM10 particulates, there are no safe levels (that is, any level of PM10 particulates has some adverse effect on health).

Figure 7.2: Electron microscope images of particulates

a) Woodburner particulates

b) pollen

c) sea salt

Source: Courtesy of Perry Davy.

Nitrogen dioxide

Nitrogen dioxide results from the combustion of fossil fuels (coal, gas, and oil) and some industrial processes.

Nitrogen dioxide has been linked to increases in asthma symptoms and reduced lung development and function in children. Nitrogen dioxide can decrease the lungs’ defences against bacteria, making them more susceptible to infections.

Traffic tends to be the main source of nitrogen dioxide emissions in the urban environment, although industry is the main source of nitrogen dioxide emissions in several locations.

Carbon monoxide

Carbon monoxide is a product of the incomplete combustion of carbon-containing fuels such as wood, coal, petrol, and diesel.

Carbon monoxide is readily absorbed by the lungs and interferes with the blood’s ability to carry oxygen. The effects of carbon monoxide exposure increase in severity as exposure increases. Foetuses and people with heart disease are the most vulnerable to elevated carbon monoxide levels.

The main sources of carbon monoxide in most urban areas are traffic and home heating.

Sulphur dioxide

Sulphur dioxide is produced during the combustion of fuels containing sulphur, such as coal and diesel.

Sulphur dioxide is a respiratory system irritant and can restrict the airways of people suffering from asthma or chronic lung disease. The effects of sulphur dioxide are worse when a person is exercising, because they draw this highly reactive pollutant more deeply into the lungs. Sulphur dioxide has also been linked to cardiovascular disease.

In most parts of New Zealand the main source of sulphur dioxide is industry. Motor vehicles are the main contributor in areas with little industry. Diesel vehicles produce higher emissions than do petrol vehicles. In Wellington, the main source of sulphur dioxide is shipping.


Ozone occurs naturally in the upper atmosphere, or stratosphere (see chapter 8, ‘Atmosphere’), where it screens out harmful ultraviolet radiation. However, at ground level, ozone affects the respiratory and cardiovascular system and can cause tissue damage to the lungs. Acute effects occur if a person is exercising in high levels of ozone.

Ground-level ozone is a secondary pollutant. It is not emitted directly but forms when volatile organic compounds (VOCs) react with oxides of nitrogen in the presence of sunlight.

Transport is a significant contributor of oxides of nitrogen and VOCs. Other sources of VOCs include home heating and some industrial processes.

Other pollutants not measured by the national environmental indicator for air

Air quality in New Zealand can be affected by pollutants that are not included as part of the national environmental indicator for air. In addition to the ambient standards, New Zealand has ambient air quality guidelines (ambient guidelines) that recommend health-based concentration limits for 15 pollutants. Table 7.2 summarises the limits set by the ambient guidelines for three pollutants that have reached elevated levels across New Zealand in the past.

Table 7.2: Ambient guidelines for other pollutants

Pollutant Recommended concentration limit


25 µg/m3 ( measured as a 24-hour average)


10 µg/m3 ( measured as an annual average reducing to 3.6 µg/m3 measured as an annual average from 2010)


0.2 µg/m3 ( measured as a three-month moving average)


(1) µg/m3 = micrograms per cubic metre.

(2) The PM2.5 concentration limit is not strictly a health-based guideline. It is recommended that levels above this limit are further investigated.

Source: Ministry for the Environment, 2002.

PM2.5 particulates

Particulate matter is composed of particles of varying sizes, but is often described as ‘coarse’ or ‘fine’.4 PM10 particulates include particulates smaller than 10 microns in diameter, and encompass both coarse and fine components. PM2.5 particulates represent the fine component alone, being solely composed of particles smaller than 2.5 microns in diameter.

Several studies indicate that PM2.5 particulates are more directly linked to negative health effects than are PM10 particulates. PM2.5 particulates can penetrate further into the lungs than can PM10 particulates, and can reach the alveoli or gas-exchange region of the lungs.

Most PM2.5 particulates come from combustion sources. Most particulate matter from natural sources (such as sea salt and soil particles) is larger than 2.5 microns in diameter.


The main sources of benzene in urban areas are transport and home heating. Benzene is emitted from the exhaust pipes of vehicles and through the evaporation of petrol. Other sources of benzene include oil refineries and petrochemical production.

Benzene is a known carcinogen that can negatively affect bone marrow, leading to anaemia and other complications.


Lead is a heavy metal that can be absorbed into the body through the lungs, stomach, and intestines. The absorption of lead can affect the development of foetuses and impair brain development in young children.

Exhaust-pipe emissions from petrol vehicles used to be a significant source of airborne lead when petrol contained lead additives to boost the octane rating. However, reductions of the lead levels in petrol in New Zealand began in 1986, culminating in the complete removal of lead additives in 1996.

Airborne lead emissions can also come from industrial activities such as metal smelting.

Limitations of the indicator

The four key limitations are listed below.

Number and type of pollutants covered

The indicator covers only the five key ambient air pollutants of national significance. In addition, it does not include indoor air pollution.

Health impacts of air quality

The indicator is set up to track air quality against limits for protecting people’s health. However, it is not able to show the health effects of air quality on people.

Furthermore, the indicator does not show synergistic effects from exposure to two or more pollutants in the environment. This is relevant because combustion processes give rise to several pollutants simultaneously.

Variations in weather and climate

The indicator reports on the state of air quality over time, but does not allow for the influence of variations in weather and climate from year to year. This makes it difficult to assess whether changes in air quality are caused by changing environmental pressures (reduction in the emission of pollutants) or meteorological variations.

Main centres of population

Before the introduction of the ambient standards in 2005, many locations had little or no nationally comparable monitoring that provided data for long-term trends of air quality. As a result, and given that the air indicator is concerned with human exposure to pollution, this chapter focuses on the following five major centres of population for which longer data sets are available: Auckland, Hamilton, Wellington, Christchurch, and Dunedin.

4  Some publications describe PM10 particulates as ‘fine’ particulates. While PM10 particulates do have a fine particulate component, they also contain a coarse component. For this reason, PM10 particulates are not called ‘fine’ particulates in this report.