Sulphur dioxide levels in air

Monitoring sites

Waikato Regional Council 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 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 was 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 was 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.

Monitoring results were 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

 *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

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

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).

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.

Monitoring sites

The amount of sulphur oxides being produced by motor vehicles, industry and home heating have been estimated for:

• Hamilton
• Tokoroa
• Te Kūiti
• Taupō
• Putaruru
• Matamata
• Waihi
• Te Awamutu
• Ngāruawāhia 
• Turangi.

Monitoring frequency

Emission summaries were completed for Hamilton, Tokoroa, Taupō and Te Kūiti every three to five years.

Monitoring history

The following table lists the years in which each town’s emission inventories were compiled.

Measurement technique

Home heating

We estimated the amount of air emissions coming from home heating using household surveys. We asked people what they use to heat their home and the quantity and type of fuel they use, for example, gas or wood. Using this information, we:

• estimated the amount of fuel used by different home heating appliances. For example, an open fire may burn about 20 kilograms of wood per day
• estimated the amount of emissions given off by different home heating appliances and different types of fuel. For example, open fires emit about 0.2 grams of SO_x per kilogram of wood.
• estimated SO_x emission rates, as grams of SO_x per kilogram of fuel burnt (g/kg). For example, a household burning 20 kilograms of wood per day on an open fire emits around 4 grams of SO_x a day, based on an emission rate of 0.2 g/kg for an open fire.

Motor vehicle emissions

Waikato Regional Council used information from area-specific ‘local road network models’ to estimate the number and types of vehicles travelling in an area. Using the Ministry of Transport’s data for average vehicle emission rates, we estimated the amount of emissions coming from motor vehicles in a given area.

Industrial emissions

We use the information contained in resource consent file at Waikato Regional Council to estimate emissions from industry. Emission estimates were calculated based on daily fuel use or activity and the use of either average industrial emission rates for that process type or emission-specific information for the site. Where there was no New Zealand specific data, we used average emission rates from the United States.

Emissions of SO_x from industry, vehicles and home heating were calculated as the daily winter average. The total daily emissions of SO_x (kg/day) from each source in an area were combined, and each source then calculated as a percentage of this total.

There were some variations in the methodology used in the 1997 and 2001 emission inventories. This made direct comparisons of results difficult.

Hamilton inventories for 2001 relied on the 1997 industrial emissions assessment, which were not re-evaluated in 2001. Tokoroa and Te Kūiti inventories for 2001 relied on the 1997 industry and motor vehicles inventories, which were not re-evaluated in 2001. Results for the 2004 inventories for Taupō, and Tokoroa indicate industrial emissions for 1997 were overestimated.