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Methods - how we monitor

Where and how we collect the data

Waikato Regional Council has measured sulphur dioxide (SO2) levels in Hamilton at the Ohaupo Road (Blood bank) monitoring station and in Tokoroa at the Billah Street reserve monitoring station. 

Monitoring sites

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

monitoring sites monitoring sites

(Map source: LAWA)

Monitoring frequency

Sulphur dioxide concentrations were measured continuously over a six month period and logged as 10 minute averages. Hourly and 24 hour average concentrations were derived from the 10 minute data.

Monitoring history

Sulphur dioxide was monitored in Hamilton at Waikato Regional Council's Ohaupo Road (Waikato Hospital site adjacent to the Bloodbank Service) monitoring site from 1 March 2012 to 31 August 2012. This is classified as a combined Traffic/Industrial monitoring site.

Sulphur dioxide was monitored in Tokoroa at Waikato Regional Council's Billah Street reserve monitoring site from 1 December 2017 to 31 May 2018. This is classified as a residential monitoring site.

Measurement technique

Concentrations of sulphur dioxide were measured using an Ecotech EC 9850 SO2 analyser. This is a continuous analyser that measures sulphur dioxide using gas phase fluorescence. Operational aspects of the sulphur dioxide monitoring including maintenance, calibration and quality assurance were carried out by Watercare Ltd for Waikato Regional Council.

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 across 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 10% 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

 *The 'excellent' category should not be applied to PM10 because the level of detection of most monitoring methods is not accurate enough.

Table 2: 2012 one-hour sulphur dioxide levels at Hamilton

Year

Categories

99.7
%ile1 (µg/m3)

Maximum value (µg/m3)

Number of times levels exceeded the NES

Excellent

Good

Acceptable

Alert

Action

2012

100%

0%

0%

0%

0%

18.1

21.2

0

 

Table 3: 2012 24-hour sulphur dioxide levels at Hamilton

Year

Categories

99.7
%ile1(µg/m3)

Maximum value (µg/m3)

Number of times levels exceeded the Regional guideline

Excellent

Good

Acceptable

Alert

Action

2012

100%

0%

0%

0%

0%

8.7

8.7

0

Guidelines and standards

National and regional ambient air quality guidelines for sulphur dioxide are:

  • 350 µg/m3 – 1 hour average.
  • 120 µg/m3 – 24 hour average.

National Environmental Standards for Air Quality for sulphur dioxide are:

  • 350 µg/m3 – 1 hour average (9 allowable exceedances per year).
  • 570 µg/m3 – 1 hour average (not to be exceeded).

Limitations

Waikato Regional Council has carried out sulphur dioxide monitoring in Hamilton and Tokoroa only and has no evidence to indicate that concentrations of sulphur dioxide in other areas are likely to be of concern.