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What is air pollution?

Human activities can emit gases and particles into the air. Some of these emissions can have a negative impact on air quality and can harm our health, our environment, and our economy. There are also natural sources of pollutants that influence air quality.

The main pollutants in our air are classed as either particulate matter (PM10, PM2.5) or gaseous pollutants (e.g. nitrogen dioxide (NO2), carbon monoxide (CO), carbon dioxide (CO2), sulphur dioxide (SO2) and ozone (O3)). These include both harmful emissions to human health and greenhouse gas emissions that contribute to climate change.

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. Air pollution can also occur during winter months when temperature inversion conditions can ‘trap’ pollutants so they do not disperse as usual.

Where do transport-related pollutants come from?

Most transport-related air pollution is exhaust emissions from motor vehicles, resulting from the combustion of petrol and diesel fuels.

There has been a reduction in pollution from individual vehicles as New Zealand’s vehicle fleet modernises, and fuel efficiency and pollution controls improve. However, an increase in the number of vehicles, distances travelled and the number of diesel-fuelled vehicles has offset some of this reduction.

Other sources of air pollution from transport include brake and tyre wear, and airborne dust generated by travelling on sealed and unsealed roads. Air pollution may also result from road construction and maintenance.

Which air pollutants are of concern?

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 listed below. These pollutants are assessed against national standards, targets and guidelines:

  • nitrogen dioxide (NO2)
  • small particulate matter (PM10 and PM2.5, ie, less than 10 and 2.5 micrometres, respectively).

Dust and odour from construction and maintenance activities and airborne dust generated by travelling on unsealed roads can also result in amenity (nuisance) effects.

What are the health effects of air pollutants?

Air pollution (from all sources) is a risk factor for several 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 (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.

Updated Health and Air Pollution in New Zealand Study(external link)

Further information on health effects of air pollution - 'Our air 2018'(external link) 

Who is responsible for managing air quality?

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

The National Environmental Standards for Air Quality (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.

Resource Management (National Environmental Standards for Air Quality) Regulations 2004(external link)

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.

Exhaust fumes and dust from the road have soiled my house, will Waka Kotahi NZ Transport Agency pay to clean it?

There are many sources of pollutants that contribute to soiling of buildings, these do include “particulate matter” pollutants in vehicle exhaust, along with other naturally occurring and man-made pollutants, such as dust and wood smoke.

Waka Kotahi does not compensate property owners that consider their buildings have been soiled by exhaust fumes or dust from road traffic.

Road controlling authorities, such as Waka Kotahi, and local councils, do not control vehicle exhaust or road dust emissions from individual vehicles on the road. Waka Kotahi also cannot restrict the classes of vehicles (such as heavy trucks) that use roads because they might cause soiling of nearby buildings.

During design and consenting of new roads Waka Kotahi does consider the impacts of vehicle emissions on nearby communities.

Information on how Waka Kotahi assesses and manages vehicle emissions 

What are Waka Kotahi’s goals and responsibilities related to the management of air quality?

Waka Kotahi 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.

We are committed to acting in an environmentally and socially responsible manner, and give effect to the Environmental and Social Responsibility Policy 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.

We also have the following responsibility to ensure that individual vehicles comply with regulated requirements for environmental performance:

  • Development and enforcement of the Land Transport Rule: Vehicle Exhaust Emissions 2007, which sets out exhaust emission standards for vehicles entering the New Zealand fleet.

Land Transport Rule: Vehicle Exhaust Emissions 2007

How is dust from road works and construction managed?

Dust from construction and road works can cause amenity effects, such as soiling of the exterior of houses and laundry, and reducing the enjoyment of outdoor activities such as gardening, barbequing and play. In rare cases dust levels might be high enough to cause temporary health effects.

To manage dust from construction and road works, Waka Kotahi generally requires that our contractors develop and implement a management plan for activities that may cause dust and impact on nearby properties. The management plans typically include a number of good practice techniques to manage off-site dust discharges. The management measures will often include methods such as limiting dust generating works during periods of high winds, limiting the amount of “open” excavations or un-reinstated earthworks at any one time, covering of loads and wetting of haul roads, stockpiles and earthworks areas.

Information on how construction dust impacts are managed(external link)

What is Waka Kotahi doing to manage air quality?

We promote 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 Waka Kotahi’s Guide to assessing air quality impacts from state highway projects.

Guide to assessing air quality impacts from state highway projects [PDF, 1.9 MB]

Options usually focus on either reducing air pollution exposure of people living or working close to the road, or reducing the emissions from the road. Sometimes it can 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 used,such as providing information and technology to assist motorists with making smarter travel choices before or during their journeys.

We extensively monitor air quality effects related to the state highway network to assess whether air quality standards are being exceeded.

State highway maintenance activities

To minimise air pollution effects resulting from the maintenance of state highways, we require all contracted suppliers to develop and implement an Environmental and Social Management Plan, based on ISO 14001, for each network operating contract.

Environmental and Social Management Plans [PDF, 731 KB]

Vehicle emissions

We ensure that vehicles entering New Zealand comply with current exhaust emissions standards requirements. Once in service, vehicles must comply with the requirements of the Warrant of Fitness (WoF) for light vehicles or the Certificate of Fitness (CoF) for heavy vehicles. Both the WoF and CoF involve a visible smoke check to identify vehicles that are excessively smoky.

Warrant of Fitness

Certificate of Fitness

What is being done about smoky vehicles?

The government introduced requirements for smoky exhausts as part of an ongoing campaign to reduce vehicle emissions and improve public health and the environment. Since 27 October 2006, all vehicles need to pass a visible smoke check in order to get their warrant or certificate of fitness.

Visible smoke check information(external link)

Further information on smoky exhausts

In service (on road) vehicle emissions in New Zealand are governed by land transport rules:

  • The Vehicle Exhaust Emissions Rule 2007:
    • Prohibits removal of, or tampering with, a vehicle's emissions control equipment
    • Requires a vehicle to pass a five second visible smoke check during a Warrant of Fitness (external link) /Certificate of Fitness inspection
  • The Road User Rule 2004:
    • Prohibits a vehicle from emitting visible smoke for 10 or more seconds whilst being driven on the road.

Information on exhaust emission standards 

The NZ Police are responsible for enforcement of the rules relating to smoky vehicles driven on the road.

How does Waka Kotahi monitor transport-related impacts?

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

The fundamental objective of our air quality monitoring network is to collect data that can be used to make informed decisions to best manage and improve the environment. We do various types of monitoring including:

  • 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. Monitoring is carried out at around 130 sites across the state highway and local road network and includes areas representing relevant exposure, such as residences and schools.

Transport Agency Network monitoring 

All new and altered state highway projects are required to consider the current air quality in the project area so we can evaluate the project’s impacts on future air quality. We might already hold suitable data, as might regional councils or research organisations. If not, dedicated monitoring may be carried out pre-project or post-project.

Guide to assessing air quality impacts from state highway projects [PDF, 1.9 MB]

Visual assessments of dust, and in some cases dust monitoring, is carried out during road construction so any potentially adverse effects can be identified, and immediate remedial action can be taken (eg to increase the frequency of water spraying to dampen dust emissions). Odour is less commonly associated road construction activities, but occassionally odour monitoring may also be undertaken.

We also invest in research and investigative monitoring to help us learn more about emmissions and air quality impacts. This typically involves one-off studies 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 Waka Kotahi nitrogen dioxide diffusion tube monitoring network includes sites located in each region, covering all main urban areas. We began monitoring at 48 sites in 2007 and this has grown to around 130 sites covering all towns and cities with populations larger than 45,000 (representing approximately two-thirds of New Zealand's population). Sites are classified as peak sites (kerbside/high concentration), roadside sites and urban background sites. 

Nitrogen dioxide concentrations can decrease rapidly with distance from the road. For example, concentrations at some peak sites represent a highly localised impact that may extend no more than 10 metres. The average of urban background site data is typically around half the concentration of the peak sites. This also reflects the highly localised nature of nitrogen dioxide exposure.

Between 2010 and 2016, 23 monitors in Auckland, Bay of Plenty, Hamilton, Northland and Wellington (out of 92 monitors across the country with enough data to calculate a trend) had decreasing nitrogen dioxide. Three sites (one in Christchurch and two in Wellington) had an increasing trend. The rest had no definite trend.

The diffusion tubes are useful as a screening method and to assess pollutant trends. However, results should be considered as indicative only. Diffusion tubes are less accurate than the costlier regulatory continuous monitors (to assess compliance with standards) and generally overread. All but a few peak sites show concentrations below the World Health Organisation nitrogen dioxide annual air quality guideline value.

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

The Resources section of this website and via the following reports and links:

For further information contact