Report: TR06/28

Author: Jeff Smith

Abstract

This report presents results of ambient air quality monitoring carried out by Environment Waikato during 2005. 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 50µg m^-3 (24-hour average) with one allowable exceedence each year. The NES became effective from September 2005. Concentrations of PM₁₀ were measured at all locations, along with monitoring of benzene at three Hamilton sites.

Tokoroa experienced the highest PM₁₀ concentrations and greatest frequency of exceedence. During 2005, the maximum measured PM₁₀ concentration at Tokoroa was 89µg m^-3 and 30 exceedences of 50µg m^-3 were measured. This compares with a previous maximum of 97µg m^-3 measured in 2004, the same year that the maximum of 41 exceedences was observed. Unusually elevated concentrations of PM₁₀ appear to have been observed at Tokoroa between Dec 2003 – Sept 2005 and this may be related to variations of wind conditions or a baseline data anomaly caused by instrumentation error.

In Hamilton, measured PM₁₀ concentrations did not exceed 50µg m^-3. However data were not collected between 15 May – 19 July 2005 and it is entirely possible that the highest PM₁₀ concentration occurred, but was undetected, during this period. It is also possible that PM₁₀ exceedances may have occurred during this time of instrument failure. Monitoring at Hamilton was carried out using a TEOM analyser with a sample temperature of 40°C. Additional daily sampling with a gravimetric instrument is recommended during winter 2006 to verify data from the TEOM.

Monitoring of benzene at Hamilton for 12 months in 2004–2005 showed concentrations at previously monitored sites were lower than results from 2003–2004. While it is possible that this is an early indication of a declining trend, the limited monitoring period is too small to be certain. Benzene concentrations are within the current MfE guidelines, but would exceed the guideline value that will become operative in 2010.

At Te Kuiti, concentrations twice exceeded 50µg m^-3 (24-hour average) and the maximum measured 24-hour average was 54µg m^-3. In Taupo, monitoring was carried out every third day and one exceedance of 50µg m^-3 was measured in 2005, when a 24-hour PM₁₀ concentration of 52µg m^-3 was recorded. Because the sampling regime at Taupo is limited to monitoring one-day-in-three, extrapolation would suggest around three exceedances for 2005.

In general, all areas show similar seasonal variations in PM₁₀ concentrations, with higher values occurring during the winter months. Interannual trends of PM₁₀ concentrations were not apparent at any of the monitoring sites.

A new PM₁₀ monitoring site was established at Matamata in June 2005 and, while no exceedances have been observed since the monitoring commenced, the dataset is too short to allow for further analysis and interpretation of the data.

Air quality monitoring 2005 [PDF, 666 KB]