Report: TR02/21

Author: Emily Wilton (Environet)

Abstract

In 1997, an emission inventory for the areas of Hamilton, Tokoroa and Te Kuiti was undertaken by Waikato Regional Council (Noonan, 1997). The purpose of that inventory was to quantify emissions to air and evaluate the relative significance of difference sources of those emissions. A repeat of the domestic heating emission inventory was carried out during 2001 to quantify the amount of emissions at 2001 and to allow an assessment of changes in these emissions with time. Priority was given to the assessment of domestic heating emissions, as this was found in 1997 to be the major source of suspended particulate (PM10), the main contaminant of concern in these areas.

Air quality monitoring data for Hamilton, Tokoroa and Te Kuiti has found concentrations of PM10 of concern in the latter two areas. In Tokoroa, a maximum PM10 concentration of 144 g m-3 was recorded in 1999. This is three times the proposed national guideline (Ministry for the Environment) and Environment Waikato guideline of 50 g m-3 (24-hour average). Monitoring of PM10 in Te Kuiti during 1998 gave a maximum 24-hour average PM10 concentration of 47 g m-3. Whilst below the guideline value, this value falls within the "alert" MfE indicator category.

In areas where air quality management may be required, emission inventories can be used, in conjunction with other data, to determine the effectiveness of different management strategies in reducing emissions. Based on concentrations of PM10 measured in 1999 and 1997 respectively, air quality management strategies for Tokoroa and Te Kuiti should be considered.

Results of the 2001 domestic home heating survey found gas to be the most common home heating method in Hamilton with 83 per cent of households using some form or gas heating on a typical winter's night. About one-third of the households in Hamilton use solid fuel burning for domestic home heating. Overall around 13,000 households in Hamilton use wood and around 2,000 use coal. In contrast, the main method of home heating in Tokoroa and Te Kuiti is solid fuel burning. In Tokoroa, 53 per cent and 21 per cent of households use woodburners and open fires respectively. Woodburner use in Te Kuiti is slightly lower at 36 per cent and open fires are used by 24 per cent of households. Multifuel burner use is also proportionally higher in Tokoroa and Te Kuiti than in Hamilton with 9 per cent and 11 per cent of households respectively using multifuel burners. The majority of solid fuel burning households use wood, although coal use in Te Kuiti is also significant with 14 per cent of households using either a combination of wood and coal or coal alone.

About 3.6 tonnes of PM10 and 33 tonnes of CO are emitted from domestic home heating in Hamilton on a typical winter's day. This compares to just over one tonne of PM10 and less than 12 tonnes of CO in Tokoroa and less than half a tonne of PM10 and less than 4 tonnes of CO in Te Kuiti. Tokoroa has the highest area based PM10 emission rate (expressed as grams of emissions per hectare of land - g ha-1) with 1615 g ha-1 of PM10. This value is high compared to other areas e.g., 1999 data for Christchurch indicates 560 g ha-1, but is slightly lower than estimates for Huntly (1747 g ha-1).

Emissions from the burning of household and garden rubbish in the outdoors were also included in the emission inventory assessment. In Hamilton around 130 kilograms of PM10 are likely to be emitted per day as a result of outdoor rubbish burning. This compares to around 40 kilograms in Tokoroa and Te Kuiti.

A comparison of results to the 1997 emissions estimates, recalculated using 2001 emission factors, suggests PM10 emissions per hectare in Hamilton and Tokoroa have increased while the PM10 emission rate in Te Kuiti has decreased. Given this trend and the concentrations of PM10 measured in Tokoroa, management intervention for this area is required.

Hamilton, Tokoroa and Te Kuiti : Domestic Heating Emission Inventory 2001 [PDF, 1 MB]