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10 Canterbury Region
10.1 Monitoring sites and methods
Details of the eleven ambient air quality PM10 monitoring sites within the Canterbury region are shown in Table 10.1. All sites meet the neighbourhood residential criteria and the main monitoring method used is the TEOM. Other monitoring methods used in Canterbury include a beta attenuation monitor at the St Albans Packe Street monitoring site in Christchurch from 1989 to 1993 and from 1996. This analyser was operated in conjunction with a TEOM for a number of years allowing an assessment of the relationship between the two methods at that site. Additional monitoring using a high-volume sampler at the same site was also carried out during 1997 to provide three-way comparison of the monitoring methods (Foster, 1998).
Table 10.1: Ambient air quality monitoring sites for PM10 in Canterbury
View ambient air quality monitoring sites for PM10 in Canterbury (large table)
10.2 PM10 concentrations
Table 10.2 shows the results of PM10 monitoring carried out in the Canterbury region based on a fixed monitoring period from 9 am to 9 am. Results in Table 10.2 indicate the guideline value for PM10 is exceeded on around 20-30% of the winter days per year. The main monitoring method for PM10 is the TEOM (Table 10.1). Data from co-located sampling methods in 1997 indicates that the TEOM in Christchurch measures about 20-30% less PM10 than the high volume sampling method when pollution levels are elevated. Consequently most of the PM10 data reported for Canterbury are likely to underestimate PM10 concentrations relative to the high volume sampling method specified in the MfE ambient air quality guidelines (MfE and MoH, 2002).
Monitoring results show 24-hour average guideline value exceedences in all of the urban centres where air quality monitoring has been carried out. Christchurch has recorded the highest PM10 concentrations measured in the region with a maximum 24-hour average concentration of 283 µgm-3. In Timaru maximum concentrations in the order of 100 µgm-3 are common with slightly lower maximums recorded in the other urban towns. Annual average PM10 concentrations range from around 18 to 23 µgm-3.
Extrapolations of the measured number of guideline value exceedences show that if monitoring was undertaken every day during the winter months, it is likely that more exceedences of the guideline value may have occurred. This is shown in Table 10.2 as the equivalent number of days the guideline value may have been exceeded.
Figures 10.1 to 10.3 show the percentage of measured PM10 concentrations in urban areas of Canterbury within the air quality categories. Although annual fluctuations in PM10 concentrations are apparent, the data does not indicate any long-term trends in PM10 concentrations in Christchurch or Timaru. Some apparent variations in PM10 concentrations in Christchurch from the early to late 1990s is likely to reflect differences in monitoring methods rather than trends in PM10 concentrations.
Table 10.2: Summary of PM10 concentrations at ambient monitoring sites in Canterbury
View summary of PM10 concentrations at ambient monitoring sites in Canterbury (large table)
Figure 10.1: Percentage of measured 24-hour average PM10 concentrations within air quality categories at St Albans, Christchurch
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text description).Figure 10.2: Percentage of measured 24-hour average PM10 concentrations within air quality categories in Timaru
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figure at its full size (including text description).
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figure at its full size (including text description).