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1 Introduction
This technical report comprises a review of PM10 monitoring in New Zealand. This includes characterising the particle problem in New Zealand by providing an overview of existing concentrations at ambient air quality monitoring sites. While historical information is considered briefly, the focus of this report is the PM10 size fraction and measurements made over the past 10 years.
The main legislation governing air quality in New Zealand is the Resource Management Act (RMA), which was introduced in 1991. Under this Act, air quality monitoring and management are the responsibility of regional councils. Sections 35 and 30 of the RMA specifically require regional councils to monitor and manage air quality. The Ministry for the Environment develops policy and tools to help councils to do this. For PM10 this includes ambient air quality guideline values and recommendations for monitoring and managing ambient air quality (MfE and MoH, 2002; MfE, 2000). The Ministry has also developed indicators to assess the state of New Zealand's air quality as part of the Environmental Performance Indicators programme.
Prior to the introduction of the RMA, air quality monitoring and management were the responsibility of the territorial local authorities and the then Department of Health. Of the minimal air quality monitoring that was carried out in New Zealand prior to 1991, there is little information relating to the PM10 size fraction. Historically measurements focused on total suspended particulate (TSP) which was often averaged over seven days, or measured "smoke" as a proxy for particulate.
During the 1980s a number of size selective inlets were designed for the TSP monitors to capture particles, with a cut point of 10 µm because of the greater health risk of this size fraction. By the late 1980s, monitoring of the PM10 size fraction had commenced at the Christchurch and Auckland GEMS (Global Environmental Monitoring Strategy) sites. Additional PM10 air quality monitoring sites were established throughout the country during the 1990s.
The first ambient air quality guideline values for New Zealand were published in 1994 by the Ministry for the Environment (MfE, 1994). These included a 24-hour average guideline value for PM10 of 120 µgm-3 and an annual average guideline value of 50 µgm-3. These original values have been reviewed and the revised values were published in 2002 (MfE and MoH, 2002). This review includes new values for PM10 including a 24-hour average guideline value of 50 µgm-3 and an annual average guideline value of 20 µgm-3. Data for the latter guideline value are only included in this report where PM10 monitoring was carried out on greater than 15% of the days per year.
The Ministry for the Environment has published a guide for air quality monitoring and data managementwhich includes an outline of the recommended monitoring and reporting requirements for PM10 and other contaminants in New Zealand (MfE, 2000). For reporting PM10 data, the recommended averaging period is for a fixed period from midnight to midnight or a moving average that is recalculated every hour.
In this report, PM10 data is mostly reported for a fixed averaging period from midnight to midnight because this is the period that the 24-hour high volume samplers have been set to. However, for some locations (e.g. Wellington and Canterbury), data are presented for alternative averaging periods in accordance with the Councils' standard monitoring protocols. For example, Environment Canterbury reports data based on a fixed period from 9 am to 9 am and Greater Wellington (the Wellington Regional Council) uses a moving average approach for continuous data and a midday-to-midday monitoring period for gravimetric sampling. These alternative approaches are appropriate in these areas, owing to the typical daily variations in PM10 concentrations. If the midnight-to-midnight approach were used in these areas the pollution episode would be split between different reporting periods, resulting in an underestimate of PM10 concentrations relative to exposure. Where alternative averaging periods have been used, this is highlighted in the report.
A number of monitoring methods for PM10 are described as appropriate in the monitoring guide (MfE, 2000). These include gravimetric sampling, beta attenuation methods and the Tapered Elemental Oscillating Microbalance (TEOM).
Further guidance on monitoring methods is also provided in Ambient Air Quality Guidelines (MfE and MoH, 2002). This report specifies that monitoring should be carried out using US 40 CFR Part 50, Appendix J, which specifies the US reference method based on gravimetric sampling. Although not specified in Appendix J, it is assumed that methods meeting the USEPA 'equivalency' status are also acceptable, as the footnote to the recommended methods table in the guideline document specifies that "where a tapered elemental oscillating microbalance (TEOM®) is used to monitor PM10 and PM2.5, another recommended monitoring method should be co-located at the site for at least one year to calculate an appropriate adjustment factor" (MfE and MoH, 2002, p.32).
The Ministry also recommends that data be reported using the air quality categories for assessing concentrations of contaminants relative to the guideline values (MfE, 1999; MfE and MoH, 2002). Table 1.1 describes the five categories for reporting air quality data.
Table 1.1: Ministry for the Environment air quality categories
| Category | Measured value | Comment |
|---|---|---|
|
Excellent* |
Less than 10% of the guideline value |
Of little concern: if maximum values are less than a tenth of the guideline, average values are likely to be much less |
|
Good |
Between 10% and 33% of the guideline value |
Peak measurements in this range are unlikely to affect air quality |
|
Acceptable |
Between 33% and 66% of the guideline value |
A broad category, where maximum values might be of concern in some sensitive locations but generally they are at a level which does not warrant urgent action |
|
Alert |
Between 66% and 100% of the guideline value |
This is a warning level, which can lead to exceedences if trends are not curbed |
|
Action |
More than 100% of the guideline value |
Exceedences of the guideline are a cause for concern and warrants action, particularly if they occur on a regular basis |
Source: MfE (1999), MfE and MoH (2002).
* The 'excellent' category should not be applied to PM10 because the level of detection of most monitoring methods is not accurate enough.
