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  Environment » Environmental Information » Environmental indicators » Air: monitoring and reporting » Ozone levels in air » Methods - how we monitor

Methods - how we monitor

Where and how we collect the data

Ozone is monitored in Hamilton because this is the area where the greatest number of people are exposed to concentrations of ozone. Monitoring is carried out during the summer months when ozone concentrations are likely to be highest.

Higher concentrations of ozone may occur down wind of Hamilton in the rural areas. During the summer of 2005/06, monitoring for ozone may be carried out at a rural site on the outskirts of Hamilton.

Monitoring sites

Monitoring sites for this specific indicator are marked in blue below:

(Map source: LAWA(external link))

Hamilton's ozone monitoring site is at Peachgrove Road. We suspect Hamilton has the highest concentrations of nitrogen dioxide and volatile organic compounds present in the air anywhere in the Waikato. These are the pollutants that react to form ozone.

Monitoring frequency

Ozone data are collected continuously in Hamilton during the summer months (November to April) and are reported as hourly average concentrations.

Monitoring history

Monitoring for ozone in the air we breathe is not a priority in many areas of New Zealand, because conditions are not considered conducive to ozone formation. However, a 1997 report identified Hamilton as having the potential for elevated ozone concentrations. This was based on an assessment of meteorological conditions, and because of the presence of emissions of the precursor contaminants, nitrogen dioxide and volatile organic compounds.

The first monitoring of ozone was carried out in Hamilton during the summer of 2003/04.

Measurement technique

Monitoring is carried out using a Thermo Environmental model 49 ozone analyser. This uses the technique of UV absorption to determine concentrations of ozone. Concentrations of ozone are measured in parts per billion and converted to micrograms per cubic metre (µg/m3) based on standard New Zealand conversions.

How this indicator is compiled

Monitoring results are reported in relation to the Waikato Regional Plan, using the Ministry for the Environment air quality indicator reporting framework outlined in the table below. This framework is used to report on air quality for a range of contaminants relative to their respective guidelines.

Table 1: Ministry for the Environment categories for air quality

Category Value relative to guideline Comment
Excellent Less than 10% of the guideline Of little concern, if maximum values are less than a tenth of the guideline, average values are likely to be much less
Good Between 0% and 33% of the guideline Peak measurements in this range are unlikely to affect air quality
Acceptable Between 33% and 66% of the guideline A broad category, where maximum values might be of concern in some sensitive locations but generally they are at a level which does not warrant dramatic action
Alert Between 66% and 100% of the guideline A warning level, which can lead to the guideline being exceeded if trends are not curbed
Action More than 100% of the guideline Exceeding the guideline is a cause for concern and warrants action if it occurs regularly

Tables 2 and 3 show the percentage of times ozone levels fell into each category, the maximum level for the month and the number of times ozone levels went above the proposed regional guideline during the periods each site was monitored.

Table 2: Summer 2003/04 one hour carbon monoxide levels at Hamilton

Year Categories Maximum value (µg/m3) Number of times levels exceeded the proposed regional guidelines
Excellent Good Acceptable Alert Action
December 03 28% 71% 1% 0% 0% 65 0
January 04 42% 55% 3% 0% 0% 80 0
February 04 19% 80% 1% 0% 0% 56 0
March 04 54% 44% 1% 0% 0% 66 0

Table 3: Summer 2003/04 eight hour carbon monoxide levels at Hamilton

Year Categories Maximum value (µg/m3) Number of times levels exceeded the proposed regional guidelines
Excellent Good Acceptable Alert Action
December 03 8% 82% 10% 0% 0% 49 0
January 04 20% 67% 14% 0% 0% 63 0
February 04 5% 86% 9% 0% 0% 48 0
March 04 40% 55% 5% 0% 0% 46 0

Guidelines and standards

The proposed regional guidelines and national ambient air guidelines for ozone have been set at:

  • 150 µg/m3 (one hour average)
  • 100 µg/m3 (eight hour average, MfE, 2002).

In 2004 the Ministry for the Environment (2003) released National Environmental Standards for air quality which include a value for ozone of 150 µg/m3 averaged over one hour.


Waikato Regional Council only has ozone data for Hamilton. Other areas where ozone concentrations may be elevated include rural areas on the outskirts of Hamilton, and possibly on the Coromandel, as a result of transportation of emissions from the Auckland Region.

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