| Environmental Setting | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 32 5.2.3 PM2.5 PM2.5 makes up a fraction of the PM10 in the atmosphere, with the size of the fraction depending on the nature of the sources of particulate in the area. In areas where the major source of PM10 in the atmosphere is combustion related activities, such as domestic fires and traffic sources, the ratio of PM2.5 to PM10 is higher than in rural areas where there is no industry and a low population. NIWA published a report in December 2019 entitled “PM2.5 in New Zealand - Modelling the current (2018) levels of fine particulate air pollution32” (NIWA PM2.5 Report), which estimates the total annual mean PM2.5 concentration in all gazetted airsheds in New Zealand and also estimates the contributions of natural and anthropogenic sources. For Waihi, NIWA estimates that the total annual mean concentration is 5.6 µg/m3, of which 2.5 µg/m3 is from natural sources. This can be compared to the annual PM2.5 standard proposed by the MfE of 10 µg/m3. 5.2.4 Meteorology OGNZL measures meteorological parameters at a climate station located at Barry Road (monitoring Site 6.63 Met Station) – (refer to Figure 6-1). A windrose of hourly average wind speed and directions for 2013 to 2019 is shown in Figure 5-3. The prevailing winds come from the west and west-southwest directions. The strongest winds also come from these directions. Secondary winds come from the northeast, and winds from all other directions are rare. The average wind speed measured at the monitoring station since 2013 is 3.43 m/s. Calm conditions (wind speeds <0.5m/s) occurred for 10.8% of the time. Winds that exceed 5 m/s, which is the critical wind speed for the lifting of dust from unconsolidated surfaces, occur for approximately 26.3% of time. Figure 5-4 shows the distribution of wind flows at the monitoring site when wind speeds are greater than 5 m/s. The figure shows that winds with speeds greater than 5 m/s are predominantly from the west direction (for approximately 19.8% of the time). Wind direction patterns are relatively consistent throughout the year with spring having the highest average wind speeds and autumn the lowest (refer Appendix A). Similar, wind direction patterns are also observed during the day and night (refer Appendix A), although on average wind speeds are greater during the day (average wind speed 3.9 m/s) compared to the night (average wind speed 3.0m/s). The proportion of hours when wind speeds are less than 0.5m/s is greater during the night compared to the day (15.2% of the time during the night vs 5.5% during of time during the day). 32 NIWA “PM2.5 in New Zealand - Modelling the current (2018) levels of fine particulate air pollution”, prepared for the Ministry for the Environment, December 2019
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