Nitrogen dioxide concentrations

  • Image, Nitrogen dioxide concentrations.

    2018 air indicators are now available

    Nitrogen dioxide (NO2) is a gas. It can be emitted directly into the air but is often formed when nitric oxide (NO) emissions react with other chemicals in the air. Nationally, road motor vehicles are the main human-made source of nitrogen oxides (NOx is the collective term for NO2 and NO). NO2 may cause respiratory infections and reduced lung development and functioning.

    We classified Nitrogen dioxide concentrations as a case study.

    Key findings

    From 2010 to 2013, at least 95 percent of monitoring sites were ‘likely’ to be within the World Health Organization (WHO) long-term (annual) guideline for NO2 concentrations.

    • In 2013, 97 percent of monitoring sites (118 of 122) were ‘likely’ to be within the guideline.
    • The sites ‘likely’ to have exceeded the guideline were situated close to busy local roads and state highways in major urban centres.
    • No monitoring urban background sites were ‘likely’ to have exceeded the guideline.
    • When comparing NO2 concentrations at the three location types (urban background, busy local roads, and state highway):
      • average concentrations at urban background sites were much lower than those at busy local road and state highway sites

      • average concentrations at busy local road sites were greater than those at state highway sites.

    Figure 1

    Note: This ‘box and whisker’ plot shows the difference in concentrations across the three location types from 2010 to 2013. The line inside each box represents the median value, in which 50 percent of the concentrations are above and 50 percent are below. The top and bottom of each box represent the upper and lower quartiles of concentrations. The top and bottom ‘whiskers’ indicate the maximum and minimum values. Nitrogen dioxide concentrations are in micrograms per cubic metre of air (µg/m3).WHO – World Health Organization.

    Figure 2

    Note: Nitrogen dioxide concentrations are in micrograms per cubic metre of air (µg/m3). We present these regions because they have more than one monitoring site with valid data for 2007–13. Because of averaging no exceedances are shown on the graph. WHO – World Health Organization.

    Definition and methodology

    Nitrogen dioxide (NO2) and nitric oxide (NO) (collectively known as nitrogen oxides, NOx) are emitted from the combustion of fossil fuels and from natural sources such as volcanoes.

    The four main human-made sources of key pollutants in New Zealand are burning wood or coal for home heating, road motor vehicle use, industry, and household outdoor burning.

    See Relative contribution of key human-made emissions for more details on emission rates for each key source.

    This case study reports the annual concentrations of NO2 in micrograms per cubic metre (µg/m3), which we compare with the World Health Organization (WHO) long-term guideline. Exceedances occur when concentrations are above 40 µg/m3.

    The WHO long-term guideline recommends a level of protection against health risks from exposure to NO2. It does not provide complete protection, and adverse health effects can occur at concentrations below the guideline.

    The concentrations are determined from screening methods, which provide a good indication of NO2 concentrations. However, these results do not definitively say a site exceeded the guideline, so we report only by ‘likely’ exceedances.

    Data quality

    We classified Nitrogen dioxide concentrations as a case study.


     This case study is a direct measure of the ‘Airborne gases of concern to human health’ topic.  


     The accuracy of the data source is of medium quality.

    See Data quality information for more detail.

    Supporting information

    Regional council and unitary authority monitoring of nitrogen dioxide


    Page published 21 October 2015

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