Ground-level ozone concentrations met the World Health Organization (WHO) short-term guideline and the national short-term standard all of the time over the past 15 years – with the exception of one exceedance at one site.
Ground-level ozone and why it’s important
Ozone helps screen out harmful ultraviolet radiation in the upper atmosphere, where it naturally occurs. However, at ground level it can be harmful to human health as it increases the risks of respiratory and cardiovascular diseases.
Ozone is not directly emitted into the air. It is formed by chemical reactions involving nitrogen oxides, volatile organic compounds, and sunlight. The increased duration and intensity of sunlight in summer makes this primarily a summer issue. There is much international interest in ozone because concentrations are generally increasing worldwide and they regularly exceed the World Health Organization (WHO) short-term guideline in many countries.
In New Zealand, ozone concentrations remain below the short-term national standard and WHO guideline for ozone. The long, thin shape of the country and our weather 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. The exception is ozone and the pollutants that create it coming from Australia (Xie, Fisher, & Gimson, 2004).
Auckland ozone concentrations meet the WHO short-term (eight-hour) guideline for health risks all of the time, with one exception at one site over the past 15 years. A long-term guideline does not exist as most of the negative health problems are associated with high short-term concentrations.
Ozone is not directly emitted into the outdoor air, but develops through reactions with other pollutants and sunlight. High concentrations occur away from where pollutants that form ozone are emitted. This is because it takes time for the chemical reactions to occur, by which stage the chemicals have dispersed away from their source.
Because of Auckland's large volume of vehicle emissions, ozone concentrations there are expected to be the highest in New Zealand. The highest concentrations are likely to develop downstream from major roads in the city centre.
Figure 19 shows the ozone concentrations at three such sites in Auckland – Whangaparaoa, Musick Point, and Patumahoe. The data shows that concentrations meet the WHO short-term guideline all the time, but exceeded it in 2002. This was attributed to bush fires near Sydney, Australia (Xie, Fisher, & Gimson, 2004).
This graph shows Maximum ozone concentrations during 8-hour periods Selected Auckland locations 1996–2012. Visit the data files page for the full breakdown of the data.
In 2012, hourly ozone concentrations were recorded at the three Auckland monitoring sites. These results met the one-hour standard for ozone in the National Environmental Standards for Air Quality. As these are peak sites, the results suggest ozone concentrations elsewhere are likely to be low and below the one-hour ozone standard.
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