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Methods - how we monitor

Where and how we collect the data

Monitoring sites

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

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

Monitoring frequency

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

Monitoring history

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


Emission inventory

  Domestic heating Motor vehicles Industry
Hamilton 1997, 2001, 2005 1997, 2001, 2005 1997, 2005
Tokoroa 1997, 2001, 2004, 2007 1997, 2004, 2007 1997, 2004, 2007
Taupo 2000, 2004 2000, 2004 1997, 2004
Te Kuiti 1997, 2001, 2007 1997, 2007 1997, 2007
Putaturu 2006 2006 2006
Matamata 2006 2006 2006
Waihi 2006 2006 2006
Te Awamutu 2006 2006 2006
Ngaruawahia 2006 2006 2006
Turangi kiss 2006 2006 2006


The following graph shows the sources of nitrogen dioxides in each town where emission inventories were complied.

Graph showing the percentage of different sources of nitrous oxide at the different monitoring sites.

Measurement technique

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. We use this information to:

  • 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 1.6 grams of nitrogen oxides per kilogram of wood burned
  • estimate nitrogen oxide emission rates, as grams of nitrogen oxide per kilogram of fuel burnt (g/kg). For example, a household burning 20 kilograms of wood per day on an open fire emits around 32 grams of nitrogen oxides a day, based on an emission rate of 1.6 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.

How this indicator is compiled

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

Guidelines and standards

None relevant for this indicator.


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.

Further indicator developments

As we gather more information this indicator will include trends in total emissions of nitrogen oxides for each area over time.