Because emission inventory studies have only been carried out in New Zealand in the last seven years, limited information is available on trends in sources of emissions. Domestic home heating is the dominant source of wintertime particle emissions and therefore changes in home heating methods will play a key role in determining trends in most areas. These changes are likely to be area specific, although factors such as increases in electricity prices or concerns regarding supply could have nationwide implications.
Changes in emissions from motor vehicles will also impact on overall trends in PM10 emissions, although to a lesser degree in most areas. The New Zealand Transport Emission Rate model (NZTER) produced by the Ministry of Transport as a part of the vehicle fleet emission control strategy indicates a reduction in particle emissions from this source with time. The reductions are primarily associated with improved vehicle technology and are illustrated in Figure 4.1. The three levels of service (LOS) categories represent emission rates for different levels of congestion.
Future trends in other sources of other emissions are difficult to assess. Growth in industrial activities and changes in existing emissions from these processes are likely to be area specific and may depend on the extent of existing regulation. Trends in domestic home heating emissions will be influenced by changes in solid fuel burner technology and any standards placed on the installation of new appliances. In some areas, management measures relating to solid fuel burning are likely to impact on future emissions from this source.
Existing trend information from emission inventory studies is limited to an assessment for Timaru comparing 1996 and 2000 and for Christchurch comparing 1996 and 1999. While the latter area shows trends in home heating methods, with an increase in the number of households using solid fuel burning and a decrease in the use of coal, changes in emissions are minimal. This is because of the reduction in emissions associated with the decreased coal use and the conversion of older solid fuel burners to low emission burners is outweighed by the overall increase in the number of solid fuel burners (Wilton, 2001c). No significant changes in home heating trends or emissions were apparent in the 1996 and 2000 Timaru emission inventory comparison.