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Air quality monitoring for PM10 has been carried out in the Wellington region since at least 1998. The main monitoring sites are located outside Wellington City, in areas such as Lower and Upper Hutt, because PM10 concentrations in these areas are elevated during the winter months.
Details of the five ambient air quality PM10 monitoring sites within the Wellington region are shown in Table 8.1. These are all residential neighbourhood air quality monitoring sites using either the TEOM operating at a temperature setting of 40°C or high-volume sampling.
The main method of monitoring for PM10 in the Wellington region is continuous monitoring using the TEOM. In Wellington, a moving 24-hour average is calculated from these data and results are reported based on the moving average. As indicated previously, this method is consistent with the Good Practice Guide for Air Quality Monitoring and Data Management (MfE, 2000), although tends to measure concentrations less than the gravimetric method recommended in the air quality guidelines. Table 8.2 shows a summary of the PM10 concentrations based on moving PM10 averages.
While no data are available for Wellington on the relationship between the TEOM monitoring method and the high volume sampling method specified in the Guidelines document (MfE and MoH, 2002), data for other areas indicates the TEOM underestimates PM10 concentrations relative to the high volume sampler. For example, studies in Christchurch and Auckland show differences of around 20-30%. Consequently the PM10 data reported for Lower and Upper Hutt are likely to underestimate PM10 concentrations relative to the method specified in the guidelines (MfE and MoH, 2002).
Unlike PM10 concentrations in most of New Zealand, the exceedence of the guideline value at the Otaki air quality monitoring site occurred during the summer months. This site is located near the sea and it is likely that the cause of elevated concentrations during the summer months is a combination of sea spray and wind blown dusts. Further work on the filter samples is being carried out by Greater Wellington to characterise the source of elevated PM10 concentrations in rural Otaki.
As well as showing the number of 24-hour average guideline value exceedences, Table 8.2 also shows extrapolations of the data for Rural Otaki (1999), Wainuiomata (2001) and Masterton (1999). For Wainuiomata and Masterton, this shows that if monitoring was undertaken every day during May to August inclusive, and for Otaki during the summer months, it is likely that more exceedences of the guideline value may have occurred.