Report: TR 2006/52

Author: Jeff Smith

Abstract

This report presents results of ambient air quality monitoring carried out by Environment Waikato for the 12 months to September 2006. In previous years, air quality monitoring results have been reported on a calendar year basis however, starting in 2006, results are now reported for 12 months ending 1 September. Monitoring sites were located in Hamilton, Tokoroa, Te Kuiti, Taupo and Matamata.

The main air contaminant of concern in the Waikato region is suspended particles (PM₁₀). In September 2004, the Ministry for the Environment introduced a National Environmental Standard (NES) for PM₁₀ of 50 µg m^-3 (24-hour average) with one allowable exceedence each year. The NES became effective from September 2005. In the 12 months to September 2006, concentrations of PM₁₀ were measured at all locations, along with monitoring of benzene at three Hamilton sites.

The highest 24 hour average PM₁₀ concentration for the 12 months to 1 September 2006 was 89 µg m^-3 recorded at Taupo on 7 June 2006. Recorded concentrations of PM₁₀ during 2006 exceeded the ambient air quality guideline of 50 µg m^-3 on five occasions at Gillies Ave, Taupo. This might be extrapolated to around 15 exceedances over the year, because of the one-day-in-three monitoring schedule at Gillies Ave. Continuous PM₁₀ monitoring at Taupo Primary School during 2006 failed to detect any PM₁₀ exceedances, so the continuous monitoring station will be moved to a site that is more likely to represent the poorest air quality in the town.

Six PM₁₀ exceedances were recorded at Te Kuiti for the 12 months to 1 September 2006 and the maximum 24 hour PM₁₀ concentration was 69 µg m^-3 measured on 28 June 2006. Two PM₁₀ exceedances were recorded at Hamilton and the highest PM₁₀ concentration of 68 µg m^-3 was observed on 29 June 2006. In Tokoroa the highest PM₁₀ concentration of 62 µg m^-3 was observed on 29 June 2006 and nine PM₁₀ exceedances were recorded for the year.

In Hamilton, Te Kuiti and Taupo, cool and calm conditions in 2006 were associated with higher PM₁₀ concentrations and greater number of exceedances than during previous years. However, lower PM₁₀ concentrations and decreased number of exceedances occurred in Tokoroa compared with previous years. The anomaly at Tokoroa is almost certainly a consequence of spuriously high PM₁₀ data collected in 2004-2005 due to instrumentation error. Upgrade of the Tokoroa BAM in September 2005 has probably resolved this issue and subsequently resulted in accurate PM₁₀ data.

The highest 24 hour PM₁₀ concentration at Matamata was 34 µg m^-3 on 7 June 2006 and no exceedances were recorded during the year.

Passive sampling of benzene at Hamilton for 12 months to 20 September 2006 showed concentrations were lower than results from previous years. For the first time since monitoring commenced in 2003, annual average benzene concentrations at all Hamilton sites were below the guideline value of 3.6 µg m^-3 that will become operative in 2010. The most significant influence on ambient benzene concentrations in recent years is likely to have been the progressive reduction of benzene content in petrol from a nationally regulated limit of four per cent in 2002 to one per cent in January 2006.

Air Quality Monitoring 2006 [PDF, 928 KB]