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

• Hamilton
• Tokoroa
• Taupo
• Te Kuiti
• Putaruru
• Matamata
• Waihi
• Te Awamutu
• Ngaruawahia
• Turangi

Emission summaries are completed for Hamilton, Tokoroa, Taupo and Te Kuiti every three to five years.

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

The following graph shows the sources of sulphur oxides in each town where emission inventories were compiled.

Home heating

We estimate the amount of air emissions coming from home heating using household surveys. We ask 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:

• estimate the amount of fuel used by different home heating appliances. For example, an open fire may burn about 20 kilograms of wood per day
• estimate 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.
• estimate 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

Environment Waikato uses 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 can estimate the amount of emissions coming from motor vehicles in a given area.

Industrial emissions

We use the information contained in resource consent files at Environment Waikato to estimate emissions from industry. Emission estimates are 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 is no New Zealand specific data, we use average emission rates from the United States.

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

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

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

The graph below shows that local industry is an important source of sulphur oxides in Te Awamutu and Putaruru. In Tokoroa, Taupo, Te Kuiti, Waihi, Matamata, Ngaruawahia, and Turangi motor vehicles are the main source of sulphur oxides. In Hamilton, industry and home heating are almost equal sources of sulphur oxide.

All data were collected between 2004 and 2007.