7 Results and Discussion

7.1 Site performance and quality assurance

All sampling performed at all sites was as planned during 2008. The Good Practice Guide for Air Quality Monitoring and Data Management 2009 suggests that it is difficult to reach anything close to 100 per cent valid data for long-term monitoring. Site performance has therefore been evaluated against a target of 95 per cent.

The performance of continuously monitored pollutant instruments during 2008 was generally very good, all sites had annual valid data and data capture rates greater than 95 per cent with the exception of TSP at St Albans.

Table 3: Percentage valid and capture data, 2008

7.2 Carbon monoxide (CO) 2008

CO was monitored at Greers Road, Burnside. One hour and 8-hour averages have been calculated from 10-minute averages recorded by the instrument.

Summary statistics for CO and their dates are described below.

Carbon monoxide results are shown in figures 7 to 11.

At Greers Road, Burnside during the 12 month period there were no exceedences of the ambient air quality 1-hour guideline (30 mg/m³) or 8-hour National Environmental Standard (10 mg/m³).

7.3 Nitrogen oxides (NO₂ and NO) 2008

Oxides of nitrogen were 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.

Summary statistics for NO₂ and their dates for each site are described below.

Nitrogen dioxide results are shown in figures 12 to 21 (Penrose), and 22 to 31 (Burnside).

There were no exceedences of the NO₂ ambient air quality 1-hour standard (200 μg/m³) or the 24-hour guideline (100 μg/m³) during 2008 at any site in Auckland or Christchurch.

7.4 Sulfur dioxide (SO₂) 2008

Sulfur 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.

Summary statistics for SO₂ and their dates for each site are described below.

Results for Gavin Street, Penrose are shown in figures 32 to 36 and Greers Road, Burnside is shown in figures 37 to 41. There were no exceedences of the SO₂ ambient air quality 1-hour standard (350 μg/m³) or the 24-hour guideline (120 μg/m³) during 2008 at any site.

7.5 Volatile organic compounds (VOC) January–December 2008

Monitoring of VOCs was conducted at three sites, 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 2008 quarter are shown in tables 4 to 7.

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 2008 six-month and 12-month averages are described below. The benzene annual averages from all the sites are less than the AAQG 2002 guideline and are graphed in figure 1.

Table 4: VOC results (January–March 2008)

ND = Not detected.

Table 5: VOC results (April–June 2008)

ND = Not detected.

Table 6: VOC results (July–September 2008)

ND = Not detected.

Table 7: VOC results (October–December 2008)

ND = Not detected.

Figure 1: MfE benzene annual average 2008

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7.6 Particulate matter (PM₁₀) 2008

PM₁₀ is monitored at Gavin Street, Penrose and Greers Road, Burnside, using Thermo FH62-C14 BAM. Twenty-four hour averages have been calculated from 10-minute averages recorded by the instruments. All PM₁₀ concentrations are reported at standard temperature and pressure (0°C and 101.3 kPa).

Summary statistics for PM₁₀ and their dates for each site are described below.

There were no exceedences of the ambient air quality standard (50 µg/m³) in Auckland during the 12 month period. PM₁₀ for 2008 for Penrose are shown in Figures 42 to 44.

At Greers Road, Burnside, there were 11 exceedences of the 24-hour standard. Each exceedence and the date are listed in table 8 below. PM₁₀ for 2008 for Burnside are shown in figures 45 to 47. As there were exceedences at the Christchurch site, more data analysis was carried out in section 7.9. All exceedences occurred over the winter period, a time when wood burning is widely used for domestic heating. Cold winter conditions strongly influence air pollution in the region especially in calm conditions. All 12 exceedences occurred in cooler months between mid May and August 2008.

Table 8: Greers Road, Burnside PM₁₀ exceedences of the daily NES 2008

Note: National Environmental Standard for PM₁₀ = 50 µg/m³.

7.7 Total suspended particulates (TSP) 2008

TSP is measured as a seven-day average at Gavin Street, Penrose and Coles Place, St Albans. Maximum results and their dates (seven-day ending period) for each site are described below.

There were no exceedences of the Ministry of Health (MoH) guideline of 60 μg/m³ at any site. The TSP concentrations in Auckland are shown in figures 2 and 3 while Christchurch TSP concentrations are shown in figures 4 and 5.

Figure 2: Auckland TSP seven-day average 2008

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Figure 3: Auckland TSP seven-day average 1994–2008

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Figure 4: Christchurch TSP seven-day average 2008

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Figure 5: Christchurch TSP seven-day average  2002–2008

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7.8 Lead (Pb) June–August 2008

Lead is measured from seven-day averaged TSP samples to derive a three-month average at Gavin Street, Penrose and Coles Place, St Albans. The results are described in the table below. Figure 6 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 6: MfE lead three-month average results 1996–2008

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Figure 7: MfE Burnside CO 1-hour fixed average January–December 2008

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Figure 8: MfE Burnside CO 1-hour fixed average 2003–2008

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Figure 9: MfE Burnside CO 8-hour rolling average January–December 2008

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Figure 10: MfE Burnside CO 8-hour rolling average 2003–2008

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Figure 11: MfE Burnside CO annual average 2003–2008

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Figure 12: MfE Penrose NO₂ 1-hour fixed average January–December 2008

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Figure 13: MfE Penrose NO₂ 1-hour fixed average 1997–2008

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Figure 14: MfE Penrose NO₂ 24-hour fixed average January–December 2008

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Figure 15: MfE Penrose NO₂ 24-hour fixed average 1 January 1997–2008

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Figure 16: MfE Penrose NO₂ annual average 1997–2008

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Figure 17: MfE Penrose NO₂ and NO 1-hour fixed average January–December 2008

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Figure 18: MfE Penrose NO₂ and NO 24-hour fixed average January–December 2008

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Figure 19: MfE Penrose NO 1-hour fixed average 1997–2008

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Figure 20: MfE Penrose NO 24-hour fixed average 1997–2008

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Figure 21: MfE Penrose NO annual average 1997–2008

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Figure 22: MfE Burnside NO₂ 1-hour fixed average January–December 2008

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Figure 23: MfE Burnside NO₂ 1-hour fixed average 2003–2008

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Figure 24: MfE Burnside NO₂ 24-hour fixed average January–December 2008

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Figure 26: MfE Burnside NO₂ annual average 2003–2008

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Figure 27: MfE Burnside NO₂ and NO 1-hour fixed average January–December 2008

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Figure 28: MfE Burnside NO₂ and NO 24-hour fixed average January–December 2008

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Figure 29: MfE Burnside NO 1-hour fixed average 2003–2008

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Figure 30: MfE Burnside NO 24-hour fixed average 2003–2008

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Figure 31: MfE Burnside NO annual average 2003–2008

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Figure 32: MfE Penrose SO₂ 1-hour fixed average January–December 2008

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Figure 33: MfE Penrose SO₂ 1-hour fixed average 2003–2008

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Figure 34: MfE Penrose SO₂ 24-hour fixed average January–December 2008

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Figure 35: MfE Penrose SO₂ 24-hour fixed average 2003–2008

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Figure 36: MfE Penrose SO₂ annual average 2003–2008

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Figure 37: MfE Burnside SO₂ 1-hour fixed average January–December 2008

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Figure 38: MfE Burnside SO₂ 1-hour fixed average 2003–2008

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Figure 39: MfE Burnside SO₂ 24-hour fixed average January–December 2008

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Figure 40: MfE Burnside SO₂ 24-hour fixed average 2003–2008

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Figure 41: MfE Burnside SO₂ annual average 2003–2008

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Figure 42: MfE Penrose PM₁₀ 24-hour fixed average January–December 2008

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Figure 43: MfE Penrose PM₁₀ 24-hour fixed average 2003–2008

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Figure 44: MfE Penrose PM₁₀ annual average 2003–2008

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Figure 45: MfE Burnside PM₁₀ 24-hour fixed average January–December 2008

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Figure 46: MfE Burnside PM₁₀ 24-hour fixed average 2003–2008

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Figure 47: MfE Burnside PM₁₀ annual average 2003–2008

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7.9 Analysis of exceedences

7.9.1 Exceedences at Greers Road, Burnside

The only exceedences recorded during 2008 were at Greers Road, Burnside, for PM₁₀ daily averages. All the other parameters monitored at all sites were below the national environmental standards (NES) for air quality.

Time of year

The PM₁₀ standard of 50 µg/m³ was exceeded 11 days in 2008 during the cooler months from May to August. During May there were three consecutive days that incurred exceedences (28–30 May). During June there were two consecutive days that incurred exceedences (20–21 June).

Time of day

The typical diurnal trend in PM₁₀ during winter is shown in figure 48. Here PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ are plotted against time of day. From figure 48, the biggest contributions to PM₁₀ were between the hours of 18:00 and 03:00. This would suggest contributions from wood burning for home heating.

Temperature

Figures 49, 50 and 51 plot PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ against hourly average temperature measured at 1.5 m, hourly average temperature measured at 10 m, and the difference between the hourly averages of the two temperature heights. From figure 49, the biggest contributions to PM₁₀ were when temperature measured at 1.5 m was below 10°C. From figure 50, the biggest contributions to PM₁₀ were when temperature measured at 10 m was below 12°C. From figure 51, the biggest contributions to PM₁₀ were when temperature difference between 10 m and 1.5 m was greater than zero, ie, when temperature inversion conditions prevailed. This is consistent with the trapping of pollutants and subsequent higher concentrations expected during temperature inversion conditions.

Relative humidity

Figure 52 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ against hourly average relative humidity (RH). From figure 52, contribution to PM₁₀ began when RH was above 60 per cent and peaked at around 90 per cent, ie, high RH conditions. This is consistent with diurnal RH and temperature patterns throughout the day.

Wind direction

Figure 53 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ against hourly average wind directions. From figure 53, no wind direction seems to contribute significantly higher concentrations than others. This is consistent with an area wide diffuse (as opposed to point/line) source of pollution. There were very few data points in the sector 120 degrees to 180 degrees as wind frequency from this sector is usually low.

Wind speed

Figure 54 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ against hourly average wind speeds. From figure 54, contributions to PM₁₀ began when wind speed was below 1.5 m/s and peaked at a wind speed of 0.5 m/s, ie, low wind speed conditions. This is consistent with reduced dispersion under low wind speed conditions.

NO

Figure 55 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ against hourly average NO. From figure 55, a positive linear relationship seems to exist between PM₁₀ and NO concentrations. This relationship is more defined at PM₁₀ concentrations below 60 μg/m³ and NO concentrations below 80 μg/m³. This is expected as PM₁₀ and NO is co-generated during the burning of wood and fossil fuels.

CO

Figure 56 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ against hourly average CO. From figure 56, a positive linear relationship seems to exist between PM₁₀ and CO concentrations. This relationship is more defined at PM₁₀ concentrations below 60 μg/m³ and CO concentrations below 2.5 µg/m³. This is expected as PM₁₀ and CO is co-generated during the burning of wood and fossil fuels. This is also expected due to meteorological conditions during winter.

SO₂

Figure 57 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 μg/m³ against hourly average SO₂. From figure 57, the relationship between PM₁₀ and SO₂ concentrations seems to depend on the exceedence day. On a few days there seems to be a positive trend although this is probably due to meteorological conditions.

Conclusions

From the comparisons of available meteorological parameters and other pollutants as discussed above, it can be concluded that the PM₁₀ exceedences were most likely due to home heating during the colder months, especially in the evenings, worsened by temperature inversions trapping the pollutants and low wind speed conditions preventing effective dispersion of pollutants.

Figure 48: MfE Burnside PM₁₀ vs time of day

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Figure 49: MfE Burnside PM₁₀ vs 1.5 m temperature

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Figure 50: MfE Burnside PM₁₀ vs 10 m temperature

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Figure 51: MfE Burnside PM₁₀ vs temperature difference 10 m–1.5 m

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Figure 52: MfE Burnside PM₁₀ vs relative humidity

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Figure 53: MfE Burnside PM₁₀ vs wind direction

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Figure 54: MfE Burnside PM₁₀ vs wind speed

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Figure 55: MfE Burnside PM₁₀ vs NO

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Figure 56: MfE Burnside PM₁₀ vs CO

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Figure 57: MfE Burnside PM₁₀ vs SO₂

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