PM10 monitoring in Reefton – Winter 2006
PM10 concentrations were continuously measured for the first time using a Beta Attenuation Monitor (BAM). In previous years a High-Vol was used measuring once every three days. The national guideline of 50 µg/m3 was exceeded 16 times with a highest daily mean of 85.5 µg/m3, which is substantially higher than the maximum concentration of 55 µg/m3 measured in 2003.
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Summary of air quality monitoring results.
Westport and Reefton had similar concentrations of PM10, with 3 and 4 samples (respectively) above national guidelines. PM10 concentrations in Greymouth were much lower with no exceedence of guidelines. Concentrations in Hokitika are likely to intermediate between those measured in Greymouth and in Westport, while in Runanga concentrations are likely to be marginally higher than those measured in Greymouth. Sulphur dioxide concentrations were low Greymouth, Hokitika and Runanga. Westport and Reefton had similar or higher concentrations without exceedence of guidelines. Benzene concentrations were low in all towns well below the Guideline of 10 µg/m3 as an annual average.
Air quality in Reefton and Westport compares favourably to cities/towns such as Christchurch, Alexandra, Kaiapoi, Timaru, Nelson and Richmond which all had maximum PM10 concentrations over 100% of guidelines. The number of exceedences per year for Reefton and Westport are slightly above and equal to (respectively) the median for all New Zealand towns where ambient air quality monitoring is conducted. Such monitoring is usually only undertaken for localities with over 1000 people and were there are significant sources of air pollution. The maximum measured PM10 concentrations on the West Coast are about one quarter of the maximum 24-hour average concentrations in Christchurch.
Air pollution in West Coast towns in winter results predominantly from domestic solid fuel burners. Such pollution is strongly affected by meteorological conditions. Wind speeds in Reefton are very low, causing frequent temperature inversions during particularly cold winter weather. However, Westport has the highest wind speeds and lowest frequency of calms compared with Reefton and Greymouth, but showed the highest levels of pollution. The prevailing wind in Westport is a light southerly to east-south-easterly, which blows along the long axis of the town. This gives the longest distance of wind travel over built-up areas from which emissions can be accumulated, and this is probably a factor in the high concentrations found. However this factor is unlikely to explain fully the concentrations being as high as they are compared with Greymouth and Reefton. The lower frequency of calm conditions in Greymouth compared with Reefton is consistent with the low levels of PM10 in Greymouth. The much lower concentrations of sulphur dioxide in Greymouth are evidently associated with lower sulphur content of coal burned in Greymouth than in Westport and Reefton.
An assessment of the health risks for the people living in the West Coast towns indicates that exposures to PM10 concentrations constitute the largest risk compared to other pollutants. The best estimate of mortality in the 5 towns monitored in this programme is that 5-8 premature deaths per year may be attributable to PM10 exposures on the West Coast. Two or three of these is estimated to occur in Greymouth and Runanga combined, where the largest population is located, although the mortality risks per 1000 population are lowest there. Although the mortality risks per 1000 population are highest in Reefton, the small population there means that about 1 premature death every 2 years is predicted. One or two premature deaths per year are predicted for each of Westport and Hokitika, but in the absence of measured PM10 concentrations in Hokitika, the estimate for that town is quite uncertain. It is possible that all these estimates are too high because of the small size of the West Coast towns. A higher proportion of the people living in small towns are adjacent to open areas and will be exposed to lower pollutant concentrations than those living near the centre where most of the PM10 measurements were made. As a result, the mortality risks reported above may be slightly overestimated.
No adverse health effects are anticipated from the measured concentrations of sulphur dioxide. These concentrations are below the MfE ambient air guidelines, which are based on threshold concentrations below which it is generally considered that there are no adverse health effects. There is also a negligible risk to human health from benzene concentrations found is this study.