Monitoring of PM₁₀ in New Zealand

• Foreword
• Acknowledgements
• Executive Summary
• 1 Introduction
• 2 Monitoring Methods for Particles in New Zealand
• 3 Auckland Region
• 4 Waikato Region
• 5 Bay of Plenty Region
• 6 Taranaki and Northland Regions
• 7 Gisborne and Hawkes Bay Regions
• 8 Wellington Region
• 9 Nelson, Tasman and Marlborough Districts
• 10 Canterbury Region
• 11 West Coast and Southland Regions
• 12 Otago Region
• 13 Trends in PM₁₀ Concentrations in New Zealand
• References
• About the Ministry

13 Trends in PM₁₀ Concentrations in New Zealand

The distribution of guideline value exceedences and maximum PM₁₀ concentrations across the country is shown in Figure 13.1 and Table 13.1. These data are based on conversions to a gravimetric equivalent for data collected using the TEOM (see Section 13.1) and extrapolations to annual estimates. With the exception of Wellington and Canterbury, they are for 24-hour averages based on a fixed monitoring period from midnight to midnight. For Wellington, data are based on a rolling 24-hour average for Lower and Upper Hutt and a fixed period from midday to midday for other sites. In Canterbury, all results are for the period 9 am to 9 am. Both reporting times are likely to provide a better indication of the PM₁₀ concentrations for these areas than a midnight-to-midnight averaging period. This is because the latter approach would split the pollution episodes across two days, providing an estimate of the PM₁₀ concentrations, which is less than the maximum 24-hour average exposure. Figure 13.2 shows the PM₁₀ monitoring results for each site within the air quality categories.

Results indicate that the PM₁₀ ambient air quality guideline value of 50 µgm^-3 (24-hour average) has been exceeded at the following locations:

Auckland	Napier	Christchurch
Hamilton	Wainuiomata	Mosgiel
Tokoroa	Nelson	Arrowtown
Taupo	Richmond	Rangiora
Whangarei	Whakatane	Dunedin
Rotorua	Timaru	Cromwell
Upper Hutt	Ashburton	Alexandra
Lower Hutt	Blenheim	Balclutha
Masterton	Kaiapoi
Otaki	Oamaru

In most areas, guideline value exceedences occur during the winter months under low wind speed and temperature inversion conditions. Emission inventory studies suggest domestic home heating is the main source of PM₁₀ emissions in most areas, although it is likely that motor vehicles are a key contributor in Auckland where a large proportion of the countries population resides. Air quality monitoring for that area indicates that the 24-hour average guideline value has been or is likely to have been exceeded at both the Henderson and Takapuna monitoring sites. Although annual average data for Auckland are limited, results suggest concentrations in excess of guideline values are likely to occur at Mt Eden, Takapuna and Henderson.

In the areas of Otaki and Whangarei, the measured guideline value exceedences have occurred during the summer months. Likely sources of these elevated levels include sea spray and dusts in Otaki (Perry Davy, WRC, personal communication, 2002) and dusts from local industry in Whangarei (Paul Baynham, NRC, personal communication, 2002).

It should also be noted that air quality monitoring in the areas of Canterbury, Lower Hutt, Upper Hutt, Hamilton, Te Kuiti, Rotorua and Tauranga have been carried out using the TEOM method, which underestimates PM₁₀ concentrations relative to the high-volume sampling method proposed in the ambient air quality guidelines (MfE and MoH, 2002). It is therefore possible that the areas of Tauranga and Te Kuiti also measure PM₁₀ concentrations in excess of the 2002 ambient air quality guideline values. An estimate of potential PM₁₀ concentrations in these locations based on relationships between the TEOM and high volume sampling methods for Christchurch is presented in Section 13.1.

The annual average ambient air quality guideline value is also likely to have been exceeded at a number of locations. However, the low sampling frequency of many of the sampling regimes makes annual average PM₁₀ concentration estimates difficult. Table 13.2 summarises the annual average concentrations in areas where PM₁₀ concentrations were measured on greater than or equal to 15% of the days per year. From these data, exceedences of the annual average PM₁₀ guideline value have been measured in Alexandra, Mt Eden, Henderson, Tokoroa, Nelson, Christchurch, Kaiapoi and Timaru.

Table 13.1: Maximum measured PM₁₀ concentrations and annual guideline exceedences

View Maximum measured PM₁₀ concentrations and annual guideline exceedences (large table)

Table 13.2: Annual average PM₁₀ concentrations within New Zealand

View annual average PM₁₀ concentrations within New Zealand (large table)

13.1 Impact of monitoring methods

The 2002 ambient air quality guidelines for PM₁₀ specify US 40 CFR Part 50, Appendix J as the designated monitoring method for measuring PM₁₀ and allow methods that meet the USEPA equivalency requirements (MfE and MoH, 2002). The guidelines specify, however, that if a TEOM is used, then another recommended monitoring method should be co-located with the analyser for a period of one year to calculate an appropriate adjustment factor. This specification is included in the guidelines because the sample line of the TEOM is heated to remove moisture and also results in some loss of volatiles.

The difference between the TEOM method and a gravimetric method is likely to vary with location, particularly for areas where the sources of PM₁₀ vary. Greater differences are likely to occur in areas where wood smoke comprises a substantial proportion of the PM₁₀ as this source contains a significant fraction of low molecular weight volatile organic compounds that will not be captured using the heated sample line of the TEOM.

Comparisons between PM₁₀ concentrations measured using a TEOM and a co-located alternative PM₁₀ sampling method are limited to the Christchurch St Albans site and the Auckland Takapuna site for the period 1997 to 1999. Figures 13.3 to 13.6 show some seasonal variations in the relationship between the TEOM and the alternative sampling methods at both monitoring sites, as well as the impact of different TEOM sample temperatures at the Christchurch monitoring site. Seasonal variations are likely to reflect differences in sources contributing to PM₁₀ concentrations.

Although the Christchurch comparisons are made using a beta attenuation monitor (BAM) rather than a gravimetric method, a comparison of PM₁₀ concentrations measuring using a BAM and a high volume sampler in 1998 showed a good correlation (r²=0.98) with an average difference in concentrations of about 4% (Foster, 1998).

Other areas that have measured PM₁₀ using a TEOM in New Zealand include Timaru, Ashburton, Rangiora, Kaiapoi, Lower Hutt, Upper Hutt, Hamilton, Te Kuiti, Rotorua and Tauranga. Table 13.3 shows estimates of PM₁₀ concentrations and guideline value exceedences based on the following equations derived from relationships observed in Christchurch and Auckland:

• PM₁₀ = 1.18 (TEOM) -0.25 (for TEOM at 30 ° C)
• PM₁₀ = 1.4 (TEOM) +0.06 (for TEOM at 40 ° C)
• PM₁₀ = 1.53 (TEOM) -1.6 (for TEOM at 50 ° C)

Table 13.3: Summary data estimates based on the conversion of TEOM data

View summary data estimates based on the conversion of TEOM data (large table)

These data suggest that the 24-hour average PM₁₀ guideline value may also have been exceeded in Te Kuiti. Exceedences of the annual average guideline value are also possible in Auckland, Hamilton, Te Kuiti, Tauranga, Upper Hutt, Ashburton and Rangiora. Additional studies examining the relationships between the TEOM method and other approved PM₁₀ sampling methods are required for these areas to determine site-specific adjustment factors.

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