Ground-level ozone concentrations

  • Image, Ground-level ozone concentrations.

    2018 air indicators are now available

    Ozone occurs in two regions of Earth’s atmosphere – at ground level and in the upper atmosphere. Ground-level ozone is a gas formed by chemical reactions involving sunlight, volatile organic compounds, and nitrogen oxides (the main source being vehicle emissions). It can also occur naturally, as it can move down from the ozone layer in the upper atmosphere. It is linked to increased health risks, such as respiratory and cardiovascular diseases.

    We classified Ground-level ozone concentrations as a case study.

    Key findings

    From 1996 to 2013, with one exception in 2002, ground-level ozone concentrations were consistently within the WHO short-term guideline and the national short-term standard at all three monitoring sites.

    • The one site that exceeded the guideline in 2002 was attributed to emissions from bush fires in Australia.
    • Due to their locations, Whangaparaoa, Musick Point, and Patumahoe are expected to have the highest concentrations of ground-level ozone in the Auckland region.
    Notes: Results at these monitoring sites do not necessarily represent the whole location. Suitable data were not available for all years for the Whangaparaoa site. Ozone concentrations are in micrograms per cubic metre of air (µg/m3). WHO – World Health Organization.

    Definition and methodology

    There is much international interest in ozone as concentrations are increasing and regularly exceeding the World Health Organization (WHO) short-term guideline in some countries.

    Ground-level ozone is mainly a summer issue as sunlight is a factor in its production.

    Given the time required for the chemical reactions that form ozone to take place, high concentrations of it occur well away and downwind from where the pollutants are initially emitted. New Zealand’s long, thin shape and our weather conditions are not favourable for forming high concentrations of ground-level ozone. Our geographical isolation also means ozone or ozone-generating pollutants emitted in other countries rarely reach us.

    This indicator assesses the one-hour and eight-hour concentrations of ground-level ozone, in micrograms per cubic metre (µg/m3) at all three sites. We compare the one-hour concentrations with the National Environmental Standards for Air Quality short-term standard. Exceedances occur when concentrations are above 150 µg/m3. The eight-hour concentrations are compared with the World Health Organization (WHO) short-term guideline. Exceedances occur when concentrations are above 100 µg/m3.

    The guideline recommends a level of protection against health risks from exposure to ground-level ozone. The standard sets a level of protection that must be met. Neither provides complete protection as there is no threshold concentration below which health effects do not occur.

    Data quality

    We classified Ground-level ozone concentrations as a case study.


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


     The accuracy of the data source is of high quality.

    See Data quality information for more detail.


    Published 21 October 2015

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