Executive Summary
This technical report comprises a review of the health impacts of particles less than 10 microns in diameter (PM10) although the implications of other size fractions and indicators is considered. The health impacts associated with concentrations of suspended particles include effects such as coughs, asthma symptoms, bronchitis, respiratory illness and mortality.
The science underpinning our understanding of the health impacts of particles is epidemiology. These observational studies on the relationship between concentrations of particles and health effects have been conducted in numerous locations throughout the world. Results show increases in mortality and other health effects are associated with increases in 24-hour average PM10 concentrations. The consistency and coherency of the studies have lead researchers to conclude that the effect is causal. The relationship appears to be linear and it appears that there is no threshold below which effects do not occur.
The impact of PM10 concentrations in areas of New Zealand on the health of the residents has been estimated in a number of different studies. The most extensive study was carried out by Fisher et al (2002) and estimates the number of deaths associated with PM10 concentrations from all sources and from motor vehicles based on relationships described in a study by Kunzli et al (2000). Results are reported for the four major cities (Auckland, Christchurch, Wellington and Dunedin) with other areas being collated for both the North and South Island. The estimated annual mortality rates were: 440 for Auckland, 180 for Christchurch, 80 for Wellington, 50 for Dunedin, 40 for Hamilton and 20 for Nelson (see Table 6.1 on page 16 for further data).
Risk assessments of the impact of PM10 concentrations in Christchurch and Nelson have also been carried out based on the results of studies of the health impacts of PM10 in Christchurch (Hales et al, 1999; McGowan et al, 2002). These include mortality estimates as well as hospitalisations and restricted activity days. The mortality estimates for the latter risk assessments underestimate mortality by around 4-5 times compared to Fisher et al, (2002). This is attributed to the time-series methodology of the Hales (1999) study, which associates only those deaths that occur a relatively short time after the pollution episode to PM10 concentrations. Thus they are limited to a selection of the acute impacts but do not estimate the reduced life expectancy due to long-term morbidity enhanced by air pollution.
This report estimates hospitalisations and restricted activity days for other areas within New Zealand based on relationships from McGowan (2002) for Christchurch and overseas relationships for restricted activity days (RADs). Results indicate a range in annual average hospitalisations per year in the larger cities, from around 25 in Dunedin to 200 in Auckland. Estimates of RADs in New Zealand cities range from around 90,000 per year in Dunedin to around 750,000 in Auckland. Table 6.1 on page 16 has further details.
