Skip to content

Access keys for

  • h Home
  • m Menu
  • 0 Show list of access keys
  • 2 Skip to content
  • 3 Skip to top

What are the sources of air pollution?

In New Zealand the sources of air pollution vary seasonally and by location but major contributors typically include:

  • Vehicle emissions
  • Wood burning (for home heating)
  • Industry
  • Natural occurring sources, such as dust, sea salts, and pollens.

Vehicle emissions can be a significant contributor to local air pollution, especially near heavily travelled or congested roadways, roadways located in low-lying areas or other areas with limited wind or air circulation, or during winter months when ‘inversion’ conditions at some locations can ‘trap’ pollutants and limit natural dispersion.

Where do transport-related pollutants come from?

Over the life cycle of a sealed roadway the greatest transport-related source of air pollution is exhaust emissions from motor vehicles. These emissions result from the combustion of petrol and diesel fuels.

As New Zealand’s vehicle fleet modernises there has been a reduction in pollution from individual vehicles due to increased fuel efficiency and improved pollution controls. This reduction has been tempered by increases in the number of vehicles and the distance travelled. This reduction has also potentially been offset by the increase of diesel-fuelled vehicles.

Other sources of air pollution from motor vehicles include brake and tyre wear, and airborne dust generated by travelling on sealed and unsealed roads. Air pollution may also arise from road construction and maintenance, which can release dust, odours and chemical compounds during activities such as earthworks, resealing and roadside vegetation control.

Which air pollutants are of concern?

Vehicle emissions, road dust, and state highway construction/maintenance activities can all impact negatively on our air quality.

Transport-related air pollution is of concern because many of the pollutants that are released are known to cause adverse health effects. Although there are a wide range of pollutants in the emissions, most of the health effects result from the following key indicator pollutants:

  • carbon monoxide (CO)
  • nitrogen dioxide (NO2)
  • particulate matter (PM10 and PM2.5) – small particles, less than 10 and 2.5 micrometres, respectively (there are 1000 micrometres in a millimetre).

In addition to these, dust and odour from construction and maintenance can result in significant amenity (nuisance) effects.

What are the health effects of air pollutants?

Air pollution (from all sources) is a risk factor for a number of health conditions, including respiratory infections, heart disease, chronic obstructive pulmonary disorder (COPD), stroke and lung cancer. Health effects may include difficulty in breathing, wheezing, coughing, asthma and worsening of existing respiratory and cardiac conditions. Young people, older people and people with existing health problems may be more vulnerable to the health effects of air pollutants.

The health effects of air pollution can result in increased medication use, increased doctor or emergency room visits, more hospital admissions, restricted activity days and premature death. The Updated Health and Air Pollution in New Zealand Study(external link) (HAPINZ Study) attributes a social cost to these health effects. In 2012, the HAPINZ Study estimated that the social cost to New Zealand related to air pollution health effects was approximately $8.4 billion. Of that total approximately 51% was related to naturally occurring air pollutants (eg dust and pollen), approximately 28% was as a result of domestic fires for home heating, and approximately 11% was attributed to motor vehicle emissions. The HAPINZ Study notes that the health effects and social cost of nitrogen dioxide exposure was not quantified; and as a result, the social cost of vehicle emissions may be underestimated.

Who is responsible for managing air quality?

Under the Resource Management Act 1991 (RMA), the primary responsibility for managing air quality resides with regional councils (eg Canterbury and Waikato Regional Councils) and unitary authorities (eg Auckland Council and Nelson City Council). These entities are also responsible for regulating and issuing consents for discharges of pollutants to air.

The Resource Management (National Environmental Standards for Air Quality) Regulations 2004(external link) (NES) sets minimum air quality standards at the national level. All regional councils and unitary authorities develop a regional policy statement and a regional plan to manage air quality. Some develop a specific plan related to air quality (an ‘air plan’). The standards in regional plans and policy statements must be at least as stringent as the NES.

The regional councils and unitary authorities are responsible for identifying and establishing air quality management areas (or ‘airsheds’) within their regions that exceed or are likely to exceed air quality standards. Where air quality standards are exceeded within an airshed, the councils/authorities must develop a plan to improve air quality, taking into account the unique characteristics of the airshed.

The Ministry for the Environment is responsible for development of national policies, guidance and tools to support management of air quality by the regional councils and unitary authorities.

What are the Transport Agency’s goals and responsibilities related to the management of air quality?

The Transport Agency’s Highways and Network Operations group manages nearly 11,000 kilometres of state highways. This involves planning, construction, operation and maintenance activities across New Zealand and the management of the related air quality effects.

The Transport Agency is committed to acting in an environmentally and socially responsible manner. The Transport Agency gives effect to the Environmental and Social Responsibility Policy [PDF, 32 KB] through the Environmental Plan, which sets out the strategic environmental and social vision for managing key areas, including the following air quality objectives:

A1. Understand the contribution of vehicle traffic to air quality.

A2. Ensure new state highway projects do not directly cause national environmental standards for ambient air quality to be exceeded.

A3. Contribute to reducing emissions where the state highway network is a significant source of exceedances of national ambient air quality.

The Transport Agency also has the following responsibility to ensure that individual vehicles comply with regulated requirements for environmental performance:

What is the Transport Agency doing to manage air quality?

The Transport Agency promotes a range of good management practices for assessing and addressing adverse air quality effects specifically associated with state highways.

New or altered state highways

For new or altered state highways, the planning/design stage is one of the best places to address potential environmental and air quality effects because alternative options can be considered early in a project life cycle. Options for assessment are discussed in detail in the Transport Agency’s Guide to assessing air quality impacts from state highway projects [PDF, 1.6 MB].

Options usually focus on either reducing the exposure of people close to the road or reducing the emissions from the road but can sometimes involve both approaches. Examples include:

  • Route Selection - choosing a route that moves the road away from sensitive receptors.
  • Buffer Distances - Maintaining or increasing the separation distance between the road and sensitive receptors.
  • Land Use Change - Re-zoning land adjacent to the state highway and avoiding reverse sensitivity issues.
  • Infrastructure Design - Implementing options for efficient traffic flow such as grade separation, high occupancy vehicle lanes and bus priority lanes.
  • Network Operation - Using information and technology to make the best use of transport networks to improve safety, mitigate traffic congestion, increase traveller mobility and convenience and reduce fuel consumption and emissions.

Existing state highways

Once the road is built, air quality effects can be managed by optimising how the state highway (including any tunnels) is operated and using information and technology to assist motorists with making smarter travel choices before or during their journeys.

The Transport Agency also undertakes extensive monitoring of air quality effects related to the state highway network. This information is used to assess whether air quality standards are exceeded along the state highway network. The Transport Agency promotes projects to reduce vehicle emissions (eg projects to reduce congestion/improve traffic flow) on the state highways where it is considered that the vehicle emissions are a significant source of exceedances of the air quality standards

State highway maintenance activities

The Transport Agency addresses effects arising from the maintenance of state highway assets by requiring all contracted suppliers to develop and implement an Environmental and Social Management Plan [PDF, 597 KB], based on ISO 14001, for each state highway network management area.

Vehicle emissions

The Transport Agency’s Access and Use group ensures that vehicles entering New Zealand comply with current exhaust emissions standards requirements and then once in service comply with the requirements of the Warrant of Fitness (WoF) and the Certificate of Fitness (CoF). Both the WoF and CoF involve a visible smoke check to identify vehicles that are excessively smoky.

How does the Transport Agency monitor transport-related impacts?

You can’t manage what you don’t measure.

The fundamental objective of the Transport Agency’s air quality monitoring is to collect data that can be used to make informed decisions to best manage and improve the environment. The Transport Agency undertakes various types of monitoring as follows:

  • monitoring trends for existing roads
  • assessment monitoring for new/altered roads
  • construction effects monitoring for new/altered roads
  • research and investigative monitoring.

Air quality effects resulting from vehicles using the existing state highway network are assessed annually using diffusion tubes to measure nitrogen dioxide (NO2). NO2 is generally accepted as a proxy for other motor vehicle-related air pollutants, such as particulate matter (PM10) and carbon monoxide. Monthly monitoring is undertaken at nearly 130 sites across the state highway network. Measurements are made at a variety of potential sensitive locations near state highways, including residences and schools. More information can be found in the Ambient air quality (nitrogen dioxide) monitoring network, annual report 2007 to 2013.

All new and altered state highway projects are required to consider the current air quality in the project area in order to evaluate the project’s impacts on future air quality. Suitable data may already be available from regional councils, the Transport Agency or research organisations. If not, dedicated monitoring may be undertaken early in a project’s life (“pre-project”) and sometimes also following project completion (“post-project”). For more information refer to the Transport Agency’s Guide to assessing air quality impacts from state highway projects [PDF, 1.6 MB].

Dust monitoring is commonly required during construction to manage any potentially adverse construction effects so immediate remedial action can be taken (eg to increase the frequency of water spraying to dampen dust emissions). Occasionally, odour monitoring may also be undertaken (eg if the project is being undertaken in a contaminated area).

The Transport Agency invests in research and investigative monitoring to acquire new knowledge to support the activities of the state highway group and other road controlling authorities. This monitoring typically involves one-off studies that are designed to review the effectiveness of existing policy or highlight options for new policy development (eg roadside remote sensing which is useful for identifying and assessing the key trends that influence the emissions performance of the light vehicle fleet).

All monitoring results are then compared to national and relevant international air quality guidelines and standards for human health and amenity protection.

What are the current levels and trends in transport-related air pollution?

The key tool used by the Transport Agency to measure levels and trends in transport-related air pollution is the national ambient air quality nitrogen dioxide (NO2) monitoring network. In 2007, the Transport Agency installed a national network of NO2 passive sampling tubes to determine the relative level of air pollution across the state highway network. This network has progressively grown and sampling tubes are now installed at nearly 130 sites in New Zealand (including state highway, local road and background locations).

Passive samplers are easy to operate and cost effective, so they can be installed in large numbers over a wide area giving good spatial coverage, but their results are indicative only and provide monthly rather than daily averages. Nitrogen dioxide (NO2) concentrations closely follow vehicle emissions in many situations, so nitrogen dioxide levels are generally a reasonable marker of exposure to traffic-related emissions.

Approximately 34 current sites have been monitored since 2007. At these sites there is generally an increasing trend in annual average NO2 concentrations between 2007 and 2013. The increase is potentially due to the increase in the number of vehicles in the New Zealand fleet, the increased distances travelled, and the increase in diesel-fuelled vehicles. However, in recent years the rate of NO2 concentration increase at these sites appears to be slowing, which may reflect the impact of improvements in vehicle technology counteracting some of the growth in vehicle travel or may be as a result of the state of the economy influencing vehicle movements or both.

The highest NO2 concentrations measured have occurred in urban areas both at sites located along local roads and at the State Highway. These include sites located in Auckland, Hamilton, Wellington and Christchurch. The Transport Agency and other agencies have a number of planned projects that will improve traffic flow and air quality at the majority of these sites.

More information about the Transport Agency’s monitoring network can be found in the Ambient air quality (nitrogen dioxide) monitoring network, annual report 2007 to 2013.

Where can I find more information about vehicle emissions and air quality in New Zealand?

More information may be found at the Resources section of this website and via the following reports and links:

For further information contact