Sources of carbon dioxide in air

Methods - how we monitored

• When and how we collected the data

  Monitoring sites

  The amounts of carbon dioxide being produced by motor vehicles, industry and home heating were been estimated for:

  • Hamilton
  • Tokoroa
  • Te Kūiti
  • Taupō.

  In addition, the amounts of carbon dioxide being produced by home heating were estimated for:

  • Huntly
  • Matamata
  • Putaruru.

  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.

  Town	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
  Taupō	2000, 2004	2000, 2004	1997, 2004
  Te Kūiti,	1997, 2001, 2007	1997, 2007	1997, 2007
  Putaruru	2006	2006	2006
  Matamata	2006	2006	2006
  Waihi	2006	2007	2006
  Te Awamutu	2006	2006	2007
  Ngāruawāhia	2006	2006	2006
  Turangi	2006	2006	2006

  Measurement techniques

  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. We used 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 1,600 grams of CO₂ per kilogramof wood burned.
  • estimate CO₂ emission rates, as grams of CO₂ per kilogram of fuel burnt (g/kg). For example, a household burning 20 kilograms of wood per day on an open fire emits around 32,000 grams of CO₂ a day, based on an emission rate of 1,600 g/kg for an open fire.

  Motor vehicle emissions

  We 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 used the information contained in resource consent files 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 use average emission rates from the United States.
• How this indicator is compiled

  Emissions of CO₂ from industry, vehicles and home heating are calculated as the daily winter average. The total daily emissions of CO₂ (kg/day) from each source in an area are combined, and each source is then calculated as a percentage of this total.
• Limitations

  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.