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GEMS/AMIS Air Quality Monitoring Programme Annual Report 2009

• 1 Summary
• 2 Introduction
• 3 Air Pollutants Monitored
• 4 Ambient Air Quality Guidelines and Standards
• 5 Monitoring Sites
• 6 Methods
• 7 Results and Discussion

7 Results and Discussion

7.1 Site performance and quality assurance

Monthly and annual site performance and explanations are shown in table 3, based on 10–minute averages for continuously monitored data. Per cent of valid data (V) is defined as the per cent of valid data following quality assurance adjustments. Per cent of captured data (C) is the per cent of valid data excluding calibration and maintenance.

The 2000 Ministry for the Environment Good Practice Guide for Air Quality Monitoring and Data Management suggests that it is difficult to reach anything close to 100 per cent valid data for long-term monitoring. As such, site performance has been evaluated against a target of 95 per cent for capture data and 75 per cent for valid data.

The performance of continuously monitored pollutant instruments during 2009 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, 2009

7.2 Carbon monoxide (CO), 2009

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

Summary statistics for CO and their dates are described below.

At Greers Road, Burnside during 2009 there were no exceedences of the ambient air quality one-hour guideline (30 mg/m³) or the eight-hour national environmental standard (10 mg/m³). Carbon monoxide results are shown in figures 7 to 11.

7.3 Nitrogen oxides (NO₂ and NO), 2009

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.

At Gavin Street, Penrose, there was one exceedence of the NO₂ one-hour national environmental standard (200 µg/m³) and no exceedences of the NO₂ 24-hour guideline (100 µg/m³). The 2009 NO_x results for Penrose are shown in figures 12 to 21.

The 1-hour NO₂ national environmental standard exceedence of 221.3μg/m³ was on 5 April 2009 at 13:00. The source of this exceedence was most likely from construction work. A crane was being used to move transformers 5–10 m from the Penrose monitoring site operating from 1 April to 6 April 2009. Elevated levels of NO₂ occurred throughout this period due to the construction work.

There were no exceedences of the NO₂ one-hour national environmental standard (200 µg/m³) or the NO₂ 24-hour guideline (100 µg/m³) in Christchurch during the 12-month period. The 2009 NO_x results for Burnside are shown in figures 22 to 31.

7.4 Sulphur dioxide (SO₂), 2009

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.

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

There were no exceedences of the SO₂ national environmental 1-hour standard (350 µg/m³) or the 24-hour guideline (120 µg/m³) during 2009 at any site. The 2009 SO₂ results for Gavin Street, Penrose are shown in figures 32 to 36 and Greers Road, Burnside are shown in figures 37 to 41.

7.5 Volatile organic compounds (VOC), January–December 2009

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. Results for each 2009 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 2009 six-month and 12-month averages are described below. The benzene annual averages from all the sites are less than the annual average guideline (10 µg/m³) and are graphed in figure 1.

7.6 Particulate matter (PM₁₀), 2009

PM₁₀ was monitored at Gavin Street, Penrose and Greers Road, Burnside. Twenty-four-hour averages have been calculated from 10-minute averages recorded by the instruments.

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

There was one exceedence of the 24-hour national environmental standard (50 µg/m³) at the Auckland site during 2009. This PM₁₀ exceedence of 132 μg/m³ occurred on 25 September 2009 and is the highest ever recorded at the Penrose site. Elevated levels of PM₁₀ were recorded at Penrose from 24 September at 21:10 until 25 September at 10:50. Particulate matter collected during this period was orange and originated from Australian dust storms. The 2009 PM₁₀ results for Penrose are shown in figures 42 to 44.

At Greers Road, Burnside, there were nine exceedences of the 24-hour standard. Each exceedence and the date of the exceedence are listed in table 8 below. As there were multiple exceedences at the Christchurch site, more data analysis was carried out and reported in section 7.9. The 2009 PM₁₀ results for Burnside are shown in figures 45 to 47.

Eight out of the nine 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. The PM₁₀ exceedence of 77 μg/m³ on 14 September 2009 was due to PM₁₀ sources that originated from Australia. Elevated levels of PM₁₀ were recorded at Burnside from 14 September at 09:20 until 15 September at 01:50.

7.7 Total suspended particulates (TSP), 2009

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 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.

7.8 Lead (Pb), June–August 2009

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 was monitored over a three-month period (June to August) annually.

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

7.9 Analysis of exceedences

There was one NO₂ national environmental standard exceedence at Penrose with the likely source being construction works near the monitoring station. There was also one PM₁₀ standard exceedence at Penrose due to Australian dust. The nine PM₁₀ exceedences recorded during 2009 at Greers Road, Burnside are examined below. All the other parameters monitored at all sites were below the National Environmental Standards (NES) for Air Quality.

7.9.1 Exceedences at Greers Road, Burnside

Time of year

The PM₁₀ standard of 50 µg/m³ was exceeded on eight days in 2009 during the cooler months from June to July. During June there were three consecutive days that incurred exceedences (3–5 June). On 14 September there was one exceedence linked to Australian dust.

Time of day

The typical diurnal trend in PM₁₀ during winter is shown in figure 48. 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 levels were between the hours of 18:00 and 03:00. This would suggest contributions from wood burning for home heating. On 4 June PM₁₀ concentrations remained high at night and in the morning. On 5 June elevated PM₁₀ levels occur from the early morning until 11 am. On 14 September elevated PM₁₀ levels start around 10am and remained throughout the day.

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, and 10 m, and the difference between the two temperature heights. From figure 49, the biggest contributions to PM₁₀ levels were when temperature measured at 1.5 m was below 5°C. Figure 50 shows the biggest contributions to PM₁₀ levels were when temperature measured at 10 m was below 7°C. Figure 51 shows 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). Figure 52 shows contribution to PM₁₀ levels began when RH was above 75 per cent and peaked at around 95 per cent, ie, high RH conditions. This is consistent with diurnal RH 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. Figure 53 shows no particular wind direction seems to contribute significantly higher concentrations of PM₁₀ over other wind directions. This is consistent with an area with wide diffuse sources of pollution 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. Figure 54 shows 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. On 5 June winds increased from mid-afternoon until the evening increasing dispersion and decreasing the PM₁₀ concentrations.

NO

Figure 55 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 µg/m³ against hourly average NO. Figure 55 shows a positive linear relationship seems to exist between PM₁₀ and NO concentrations. This relationship is usually 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. Figure 56 shows a positive linear relationship seems to exist between PM₁₀ and CO concentrations. This relationship is usually more defined at PM₁₀ concentrations below 60 µg/m³ and CO concentrations below 2.5 mg/m³. This is expected as PM₁₀ and CO is co-generated during the burning of wood and fossil fuels.

SO₂

Figure 57 plots PM₁₀ hourly averages for those days where the daily PM₁₀ average exceeded 50 µg/m³ against hourly average SO₂. Figure 57 shows 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 almost all of the PM₁₀ exceedences were likely due to home heating during the colder months. This is observed especially in the evenings, when PM₁₀ levels are worsened by temperature inversions trapping the pollutants and low wind speed conditions preventing effective dispersion of pollutants.

The elevated PM₁₀ concentrations on 14 September are the exception as the source was linked to Australian dust. The elevated levels occurred from 09:20 onward. With PM₁₀ concentrations greater than 50 µg/m³ the meteorological conditions for the day were warm and dry with low to gentle breezes.

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