This chapter sets out why good air quality is important, and presents information about the pressures on air quality in New Zealand, and its state and trends.
Air quality in New Zealand – a summary
Most New Zealanders enjoy good air quality most of the time. When air quality does reach levels considered unhealthy, this usually happens for limited periods in certain locations. In this way, New Zealand differs from many countries, where air pollution can be a year-round issue in cities and towns.
In New Zealand, home heating is the primary source of pollutants that cause most concern. This is a problem mainly in winter, in places where households use wood or coal to keep their homes warm. Transport is another major source of pollutants that can harm our health, usually in urban areas near busy roads. For both home heating and transport emissions, pollutants are most likely to become a problem on still, cold days, when particles are less likely to disperse.
Many factors contribute to our comparatively good air quality. New Zealand has a relatively small population and has low reliance on heavy industry compared with other developed countries. However, geographic and climatic factors are also important. New Zealand is an island surrounded by ocean, and some distance from other land masses. Therefore, unlike many parts of the world, pollution from other countries rarely affects us. Climatic factors also relate to our geography. New Zealand is a long, narrow country that sits in the path of the ‘roaring forties’, strong winds that blow to the east across the Pacific Ocean. These winds help to disperse pollutants.
The limited historical data we have for Auckland, New Zealand’s biggest city, indicates that its air quality has improved over the past 50 years. This improvement is expected to be linked to longer-term improvements due to stricter controls on industrial and other emissions from the early 1970s, a gradual but consistent shift to ‘cleaner’ forms of home heating, improvements to fuel, and stricter emission limits on new vehicles. A pollutant of particular concern, lead in petrol, was phased out in 1996, and has resulted in a reduction in lead in our air.
Since monitoring became more extensive across the country in 2006, we have seen a significant improvement in air quality overall. These improvements in air quality were driven mainly by the shift to cleaner home heating. From 2006 to 2013, estimated annual emissions of particulate matter (PM10 and PM2.5) from home heating decreased (24 percent and 23 percent, respectively).
Modelling showed a decrease in vehicle emissions, and these decreases were likely to have contributed to improved air quality. Between 2001 and 2013, estimated emissions for five key pollutants from road vehicles fell between 26 and 52 percent.
Poor air quality for even short periods can have serious health impacts. The air pollutant of most concern in New Zealand is particulate matter – the tiny airborne particles that affect respiratory and cardiovascular health. Damage to respiratory and cardiovascular systems can lead to hospital admissions, days of work lost, and shorter lives for some New Zealanders. In 2012, an estimated 1,000 premature deaths were associated with particulate matter in our air.
How we measure air quality
In New Zealand, regional and unitary councils monitor our air for a range of pollutants at sites around the country. These are usually in areas where high levels of pollutants are expected, or have been found historically, such as in towns or cities, and near busy roads.
Reporting against long-term guidelines gives a good indication of general air quality conditions. It also best represents the typical and long-term exposure at a particular location. Reporting on the short-term guidelines focuses on peak exposure events.
We report on our air quality by comparing long-term (annual) and short-term (daily and hourly) pollutant concentrations against:
- World Health Organization (WHO) 2006 long-term (annual) guideline
- Ministry for the Environment’s Ambient Air Quality Guidelines 2002, where WHO long-term (annual) guidelines do not exist (eg for arsenic and benzo(a)pyrene)
- New Zealand’s National Environmental Standards for Air Quality 2004 (daily and hourly standards).
In some cases, where WHO guidelines and national environmental standards differ (eg for sulphur dioxide), we report against both.
For some pollutants, such as nitrogen dioxide, information is collected using a screening method. The method gives good indications of concentrations, but the results cannot be directly compared with guidelines. In these cases, we state that concentrations are ‘likely’ to meet or exceed guidelines.
Types of pollutants
Air pollutants can be grouped into three broad categories: airborne particles, gases, and ‘other pollutants’.
In New Zealand, airborne particle pollutants are of most concern because of their high concentrations in some locations and their potential to cause a range of health problems, from relatively minor to severe. When larger airborne particles are inhaled, they are trapped in the nose, mouth, and nasal passages and can cause irritation. Smaller particles can travel to the lungs, where they can cause injury or be absorbed into the bloodstream, resulting in respiratory diseases, heart attacks, and lung cancer.
Particulate matter (PM) are commonly measured in two size ranges (see figure 2):
- PM10 have a diameter 10 or less micrometres
- PM2.5, a subset of PM10, have a diameter of 2.5 micrometres or less.
Note: µm – micrometre, a unit of length equal to one thousandth of a millimetre.
This image illustrates the relative size of particulate matter. It compares the size of PM10 and PM2.5 to a strand of hair and a grain of beach sand.
Airborne particles can be generated by human activities or natural sources. Burning wood and coal for home heating, transport, burning garden and other household waste outdoors, and industrial processes are examples of human activities that cause pollution.
Sea salt, pollen, airborne soil, and volcanic ash are examples of natural forms of particulates. Generally, they are bigger particles and are therefore considered to be less harmful to human health. Because particles from natural sources are larger, we do not often find them in PM2.5 concentrations. PM2.5 is therefore more indicative of airborne particles from human activities.
The smaller airborne particles are, the greater the harm they pose to human health. Smaller particles can penetrate deep into the lungs and even into the bloodstream. The WHO guideline for both daily and annual average exposure to PM2.5 is half that for PM10.
Monitoring PM10 has been mandatory in New Zealand since 2004, while monitoring PM2.5 is not mandatory. For this reason, we have more data about PM10 than PM2.5. While we have PM10 data covering most of the country, PM2.5 monitoring is limited only to Auckland, Canterbury, and Wellington.
Gases can also adversely affect our air quality and people’s health. We have good information on nitrogen dioxide concentrations in New Zealand. WHO recognises nitrogen dioxide concentrations as an indicator of air pollution from road motor vehicles. It is linked to an increase in asthma symptoms and reduced lung function. Other gases, such as carbon monoxide, sulphur dioxide, and ozone, are also monitored at some sites in New Zealand.
Other air pollutants include heavy metals and volatile organic compounds. For example, arsenic is emitted when treated timber is burnt. Benzene is a volatile organic compound emitted when vehicles burn petrol. Arsenic is associated with heart conditions and cancer, while benzene is associated with cancer, and adverse effects on the nervous system.