Sources of particles in air

The amount of PM₁₀ produced by motor vehicles, industry and home heating have been estimated for:

• Hamilton
• Tokoroa
• Te Kuiti
• Taupo
• 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.

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 10 grams of PM₁₀ per kilogramof wood burned.
• estimate PM₁₀ emission rates, as grams of PM₁₀ per kilogram of fuel burnt (g/kg). For example, a household burning 20 kilograms of wood per day on an open fire emits around 200 grams of PM₁₀ a day, based on an emission rate of 10 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 PM₁₀ from industry, vehicles and home heating are calculated as the daily winter average. The total daily emissions of PM₁₀ (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 differences 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 in Hamilton around 70 percent of particles in the air come from home fires with outdoor rubbish burning and motor vehicles each contributing just over 10 percent.  In Taupo, Tokoroa, Turangi, Ngaruawahia and Matamata domestic fires contribute around 90 percent of the particles.  In Te Kuiti, Putaruru, Waihi and Te Awamutu the contribution of domestic fires is less, at around 60 to 70, with industry contributing around 20-40 percent.