7 Results and Discussion

7.1 Site performance and quality assurance

Valid NO₂, SO₂, CO, and PM₁₀ data from the Greers Road, Burnside site were below 90 percent for the month of February due to data-logger problems early in the month (8 to 11 February 2005) and at the end of the month (25 to 28 February 2005). Valid data capture rates for these pollutants were greater than 90 percent for 2005.

Overall site performance is shown in Table 3 below based on 10-minute averages for continuously monitored data. Percent data capture is the percent of total instrument availability and includes downtime for calibration and routine maintenance. Percent valid data is defined as the percent valid data following quality assurance eg, invalidation of data resulting from calibrations, routine maintenance, spurious data and excessively negative data.

Table 3: Percentage valid and capture data 2005

View Table 3: Percentage valid and capture data 2005 (large table)

7.2 Carbon monoxide (CO) 2005

CO was monitored at Greers Road, Burnside. One-hour and eight-hour averages have been calculated from 10-minute averages recorded by the instruments.

The maximum results and their dates are described below.

Results are given in Figures 6 to 9.

Concentrations of CO at Greers Road Burnside were below the ambient air quality 1-hour guideline (30 mg/m³) and 8-hour national environmental standard (10 mg/m³) during 2005.

7.3 Nitrogen oxides (NO₂ and NO) 2005

Oxides of nitrogen were monitored at Gavin Street, Penrose; Kowhai Intermediate, Kingsland; and Greers Road, Burnside. One hour and 24-hour averages have been calculated from 10-minute averages recorded by the instruments.

The maximums for NO₂ and their dates for each site are described below.

Nitrogen dioxide results are in Figures 10 to 15 (Kowhai), 16 to 21 (Gavin Street), and 22 to 27 (Burnside).

There was one exceedance of the NO₂ ambient air quality 1-hour standard (200 µg/m³) at Gavin Street, Penrose on 19 December 2005. The NES allow for nine 1-hour NO₂ exceedances in a 12-month period. There were no exceedances of the 24-hour guideline (100 µg/m³) during 2005 at any site in Auckland or Christchurch.

7.4 Sulphur dioxide (SO₂) 2005

Sulphur dioxide was monitored at Gavin Street, Penrose and Greers Road, Burnside. One-hour and 24-hour averages have been calculated from 10-minute averages recorded by the instruments.

The maximums for SO₂ and their dates for each site are described below.

Results for Gavin Street, Penrose, are shown in Figures 28 and 29 and Greers Road, Burnside, are shown in Figures 30 and 31. There were no exceedances of the SO₂ ambient air quality 1-hour standard (350 µg/m³) or the 24-hour guideline (125 µg/m³) during 2005 at any site.

7.5 Volatile organic compounds (VOC)
January - December 2005

Monitoring of VOCs was conducted at four sites: Kowhai Intermediate School, Kingsland; Gavin Street, Penrose; Greers Road, Burnside; and Coles Place, Christchurch. VOC monitoring utilises passive sampling badges exposed over a three-month period. A set of results for each 2005 quarter are shown in Tables 4 to 7. See monitoring method in section 4.

The benzene guideline is 10 µg/m³ as an annual average with an average value of 3.6 µg/m³ to be achieved by 2010. The 2005 six-month and 12-month averages are described below.

Table 4: VOC results (January - March 2005)

Table 5 VOC results (April - June 2005)

Table 6: VOC results (July - September 2005)

Table 7: VOC results (October - December 2005)

7.6 PM₁₀ 2005

PM₁₀ is monitored at Greers Road, Burnside, using a thermo FH62-C14 beta gauge. PM₁₀ results measured by Auckland Regional Council at Gavin Street, Penrose and Kowhai Intermediate, Kingsland sites, also using thermo FH62-C14 beta gauges, are also included in this report. Twenty four-hour averages have been calculated from 10-minute averages recorded by the instruments. All PM₁₀ data is reported at standard temperature and pressure (0°C and 101.3 kPa).

The maximums for PM₁₀ and their dates for each site are described below.

There were no exceedances of the ambient air quality standard (50 μg/m³) at Gavin Street, Penrose or Kowhai Intermediate, Kingsland during the 12-month period.

At Greers Road, Burnside there were 18 exceedances of the 24-hour standard. Each exceedance and the date is listed in Table 8 below. Charts describing 24-hour averaged data for 2005 for each site are shown in Figures 32 to 33 (Kowhai), 34 to 35 (Gavin Street), and 36 and 37 (Burnside). As there were exceedances at the Christchurch site, more data analysis was carried out in Figures 38 to 41. All exceedances occurred over the winter period, a time when wood burning is widely used to heat homes. As reported by Environment Canterbury, cold winter conditions strongly influence air pollution in the region. A total of 14 exceedances occurred during the period June to July, with only four exceedances occurring during the months of April, May and August 2005.

Table 8: Greers Road, Burnside PM₁₀ exceedances of the daily NES 2005

Note : National environmental standard for PM₁₀ = 50 µg/m³.

7.7 Total suspended particulates (TSP) 2005

TSP is measured as a seven-day average from Gavin Street, Penrose; Kowhai Intermediate, Kingsland; and Coles Place, St Albans. Maximum results are shown in the table below.

There were no exceedances of the Ministry of Health's guideline of 60 μg/m³ at any site. The data from each site is described in Figures 1 and 2 below.

Figure 1: Auckland TSP seven-day average 2005

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Figure 2: Auckland TSP seven-day average 1994 - 2005

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Figure 3: Christchurch TSP seven-day average 2005

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Figure 4: Christchurch TSP seven-day average 2002 - 2005

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7.8 Lead (Pb) June - August 2005

Lead is measured from seven-day averaged TSP samples to derive a three-month average. The results are described in the table below. Figure 5 provides moving three-month averaged lead data between January 1996 and September 2000, when lead monitoring was performed on a monthly basis. From this point, lead continued to be monitored over a three-month period (June to August) annually.

No site exceeded the three-month average guideline for lead (0.2 µg/m³).

Figure 5: MfE lead three-month average results 1996 - 2005

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Figure 6: MfE Burnside CO 1-hour fixed average January - December 2005

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Figure 7: MfE Burnside CO 1-hour fixed average 1 January 2003 - 31 December 2005

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Figure 8: MfE Burnside CO 8-hour rolling average January - December 2005

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Figure 9: MfE Burnside CO 8-hour rolling average 1 January 2003 - 31 December 2005

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Figure 10: MfE Kowhai NO₂ 1-hour fixed average January - December 2005

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Figure 11: MfE Kowhai NO₂ 1-hour fixed average 1 January 2004 - 31 December 2005

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Figure 12: MfE Kowhai NO₂ 24-hour fixed average January - December 2005

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Figure 13: MfE Kowhai NO₂ 24-hour fixed average 1 January 2004 - 31 December 2005

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Figure 14: MfE Kowhai NO₂ and NO 1-hour fixed average January - December 2005

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Figure 15: MfE Kowhai NO₂ and NO 24-hour fixed average January - December 2005

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Figure 16: MfE Gavin Street NO₂ 1-hour fixed average January - December 2005

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Figure 17: MfE Gavin Street NO₂ 1-hour fixed average 1 January 1997 - 31 December 2005

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Figure 18: MfE Gavin Street NO₂ 24-hour fixed average January - December 2005

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Figure 19: MfE Gavin Street NO₂ 24-hour fixed average 1 January 1997 - 31 December 2005

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Figure 20: MfE Gavin Street NO₂ and NO 1-hour fixed average January - December 2005

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Figure 21: MfE Gavin Street NO₂ and NO 24-hour fixed average January - December 2005

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Figure 22: MfE Burnside NO₂ 1-hour fixed average January - December 2005

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Figure 23: MfE Burnside NO₂ 1-hour fixed average 1 January 2003 - 31 December 2005

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Figure 24: MfE Burnside NO₂ 24-hour fixed average January - December 2005

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Figure 25: MfE Burnside NO₂ 24-hour fixed average 1 January 2003 - 31 December 2005

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Figure 26: MfE Burnside NO₂ and NO 1-hour fixed average January - December 2005

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Figure 27: MfE Burnside NO₂ and NO 24-hour fixed average January - December 2005

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Figure 28: MfE Gavin Street SO₂ 1-hour fixed average January - December 2005

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Figure 29: MfE Gavin Street SO₂ 24-hour fixed average January - December 2005

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Figure 30: MfE Burnside SO₂ 1-hour fixed average January - December 2005

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Figure 31: MfE Burnside SO₂ 24-hour fixed average January - December 2005

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Figure 32: MfE Kowhai PM₁₀ 24-hour fixed average January - December 2005

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Figure 33: MfE Kowhai PM₁₀ 24-hour fixed average 1 January 2004 - 31 December 2005

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Figure 34: MfE Gavin Street PM₁₀ 24-hour fixed average January - December 2005

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Figure 35: MfE Gavin Street PM₁₀ 24-hour fixed average 1 January 2003 - 31 December 2005

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Figure 36: MfE Burnside PM₁₀ 24-hour fixed average January - December 2005

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Figure 37: MfE Burnside PM₁₀ 24-hour fixed average 1 January 2003 - 31 December 2005

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7.9 Analysis of exceedances

7.9.1 PM₁₀ exceedances at Greers Road, Burnside

Environment Canterbury noted one of the mildest winters on record for Christchurch in 2005. Although light winds and clear sunny days were prevalent during the winter period, evening cloud brought about by a series of anticyclones created warmer temperatures. These favourable conditions may have contributed to a reduction in PM₁₀ exceedances (25 exceedances in 2004 compared with 18 exceedances in 2005). [Environment Canterbury. 2005. Winter Air Report. http://www.ecan.govt.nz/Our+Environment/Air/Winter+Reports.]

A 72-hour period from 7 to 9 June 2005 was chosen as a typical example of winter diurnal trends coinciding with PM₁₀ exceedances to describe the relationship between pollution levels and meteorological conditions. Figure 38 provides an example of the typical diurnal trend in air pollution during this period. Figures 39 to 41 present the meteorological conditions that influence the diurnal trend. It is apparent when comparing wind speed (Figure 39) and PM₁₀ concentrations (Figure 38) that low wind speeds coincide with PM₁₀ peaks and conversely higher wind speeds coincide with low PM₁₀ concentrations. Reduced air mixing caused by low wind speeds results in poor dispersion of pollution while an unstable atmosphere caused by high wind speeds is conducive to pollution dispersion.

Low temperatures, often coinciding with still atmospheric conditions, can cause temperature inversions. This can contribute to higher PM₁₀ concentrations being measured as pollution is trapped at ground level. A comparison of temperatures measured at 1.5 and 10 m (Figure 40) does not indicate the presence or absence of a temperature inversion as the inversion height may be greater than 10m, however, a diurnal trend is apparent. As the temperature drops during the evening, Christchurch residents light their heating appliances causing particle emissions to increase and PM₁₀ levels to peak just before midnight. As the fires die down and the atmosphere becomes more unstable toward morning, concentrations of PM₁₀ drop off.

A pollution rose for the same 72-hour period (Figure 41) that describes the relationship between wind direction and PM₁₀ concentrations shows no obvious pattern. This would suggest that the incidents are not directly related to very localised sources of PM₁₀ but are perhaps more related to prevailing meteorological conditions such as temperature inversions.

Figure 38: MfE Burnside PM₁₀, typical winter diurnal trend, 10-minute fixed average 7-9 June 2005

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Figure 39: MfE Burnside wind speed, typical winter diurnal trend, 10-minute fixed average 7-9 June 2005

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Figure 40: MfE Burnside ambient temperature, typical winter diurnal trend, 10-minute fixed average 7-9 June 2005

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Figure 41: MfE Burnside pollution rose, 10-minute average 7-9 June 2005

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7.9.2 NO₂ exceedance at Gavin Street, Penrose

The NO₂ exceedance occurring on 19 December 2005 was investigated and found to be caused by machinery and trucks operating during construction works at the Gavin Street substation, several metres to the east and northeast of the air quality monitoring shed. Figures 42 and 43 provide NO₂ exceedance data for 19 December 2006. Other pollutants were also elevated at Gavin Street during this time (PM₁₀ and SO₂), as described in Figures 44 and 45 below. Figure 46 shows the relationship between wind direction and pollution levels monitored on 19 December 2005.

Figure 42: MfE Gavin Street NO₂ exceedance 10-minute average 19 December 2005

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Figure 43: MfE Gavin Street NO₂ exceedance 1-hour average 19 December 2005

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Figure 44: MfE Gavin Street SO₂ 1-hour average 19 December 2005

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Figure 45: MfE Gavin St PM₁₀ 1-hour average 19 December 2005

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Figure 46: MfE Gavin Street pollution rose 10-minute average 19 December 2005

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