4 High Risk Areas in New Zealand
Monitoring of PM10 concentrations has been carried out in most of the main urban areas within New Zealand. Summary information on PM10 concentrations relative to the air quality categories are shown in Figure 4.1. While results are generally comparable, measurements in some areas (e.g. Richmond) were made predominantly during the winter when PM10 concentrations are highest, thus biasing results to the worst case. A more detailed discussion of the monitoring period, methods and results is presented in the report Monitoring of PM10 in New Zealand (MfE, 2003).
In many urban areas within the South Island of New Zealand, PM10 concentrations regularly exceed the 24-hour average ambient air quality guideline value of 50 µgm-3 (MfE and MoH, 2002). In many areas meteorological conditions are particularly conducive to elevated pollution levels, with temperature inversions and low wind speeds restricting vertical and horizontal mixing and pollution dispersion. Some of the worst areas, as indicated by maximum 24-hour average PM10 concentrations, are Christchurch, Timaru, Nelson, Alexandra and Kaiapoi (Figure 4.2).
While maximum 24-hour average PM10 concentrations are not generally as high in the North Island, many areas experience concentrations in excess of the ambient air quality guideline value. In particular, 24-hour average PM10 concentrations in specific urban areas within the Wellington and Waikato regions are of concern. Also of concern in the North Island are annual average PM10 concentrations measured in Auckland of around 28 µgm-3, which are approximately 40% above the annual guideline value of 20 µgm-3 (MfE and MoH, 2002). Unlike most urban areas in New Zealand, PM10 concentrations in Auckland do not show strong seasonal variations. This may indicate the dominance of less season specific sources such as motor vehicles and sea spray. Other areas where elevated PM10 concentrations are common during the summer months include Whangarei and Otaki. Possible sources in these areas include local industry, and sea spray and dusts respectively.
The sources of PM10 may have some importance when considering the health implications. Although the role of factors such as particle size and composition are not yet fully understood, it is likely that PM10 measurements in New Zealand can be used to provide a good indication of the extent of health impact. Some exceptions may occur in locations such as Otaki and the Christchurch suburb of Sumner, where sea spray is thought to be a significant contributor to measured PM10 concentrations. As indicated previously, it is possible that some health effects associated with particles do not apply to sources such as sea spray. Similarly estimates of health impacts based on extrapolation of studies from other areas may be a bit speculative in areas where dusts or other sources of coarser PM10 (e.g. industrial processes) are a dominant contributor.
Figure 4.1: The percentage of measured 24-hour average PM10 concentrations within air quality categories in New Zealand
Figure 4.2: Maximum 24-hour average PM10 concentrations in New Zealand measured between 1997 and 2001
