4 Sulphur Dioxide (SO2)
Concentrations of sulphur dioxide have been measured within a number of urban centres in New Zealand. Results of this monitoring are compared to the following ambient air quality guideline values for New Zealand:
- 350 mgm-3 (one-hour average)
- 120 mgm-3 (24-hour average).
The recommended monitoring method for sulphur dioxide in New Zealand is AS3580.4.1 - 1990. This method specifies fluorescence. Unless stated otherwise, all data presented in this section are based on monitoring methods that comply with AS3580.4.1 - 1990, which is the recommended method in the Good Practice Guide for Air Quality Monitoring and Data Management (MfE, 2000) and is the required method in the Ambient Air Quality Guidelines (MfE and MoH, 2002). The former report also indicates that some measurements of SO2 in New Zealand have been made using passive sampling and wet chemical techniques. The latter are a measure of total acidity and are not an accurate method for assessing SO2 concentrations.
4.1 Auckland region
Concentrations of SO2 have been measured in Auckland at the Penrose (ACI) monitoring site since 1990. Summary results of monitoring from 1992 to 2001 are shown in Table 4.1. Figure 4.1 shows the percentage of 24-hour average SO2 concentrations from 1992 to 2001 and one-hour average concentrations for 2001, by month, within the air quality categories. The monthly data suggests some seasonal variations with slightly higher SO2 concentrations during the winter months. However, most 24-hour and one-hour average SO2 concentrations are within the 'excellent' and 'good' categories.
Table 4.1: Summary data for SO2 monitoring in Auckland
View summary data for SO2 monitoring in Auckland (large table)
Figure 4.1: Percentage of measured one-hour and 24-hour average SO2 concentrations within air quality categories at Penrose, Auckland
See figure 4.1 at its full size (including
text description).
4.2 Taranaki region
Air quality monitoring for SO2 in Taranaki includes passive sampling carried out by NIWA around the time of the Mt Ruapehu eruptions during 1997 and 1998, some state of the environment monitoring and some site specific monitoring to assess the impact of a local fertiliser plant. Results of air quality monitoring are detailed in a Taranaki Regional Council Report (2002). This indicates that the ambient air concentrations of SO2 that have been measured in Taranaki are 'excellent'. The site specific monitoring around the Ravensdown site (Table 4.2) shows elevated concentrations during the 1996 and 1997 period. However, concentrations measured during 1997-98 after the shutdown of the sulphuric acid plant, the superphosphate manufacturing plant and the chrome sulphate plant were considerably lower.
Table 4.2: Ambient SO2 monitoring results from around the Ravensdown site for 1996-97 and 1997-98 monitoring periods
4.3 Hawkes Bay region
In the Hawkes Bay area, monitoring of SO2 was carried out in Hastings in 1994 and 1998. Figure 4.2 shows the percentage of SO2 concentrations within the air quality categories for the months September to November 1998. The maximum one-hour and 24-hour average concentrations measured were 9 µgm-3 and 5 µgm-3 respectively (Table 4.3).
Table 4.3: Summary data for SO2 monitoring in Hawkes Bay
| One-hour average |
Hastings 1998 |
24-hour average |
Hastings 1998 |
|
|---|---|---|---|---|
|
% valid data |
12% |
% valid data |
12% |
|
|
Hours > 350 µgm-3 |
0 |
Days > 120 µgm-3 |
0 |
|
|
99.9 %ile µgm-3 |
9 |
99.9 %ile µgm-3 |
5 |
|
|
Maximum µgm-3 |
12 |
Maximum µgm-3 |
5 |
Figure 4.2: Percentage of measured one-hour and 24-hour average SO2 concentrations within air quality categories in Hastings, 1998
See figure 4.2 at its full size (including
text description). 4.4 Canterbury region
Concentrations of SO2 are measured at most monitoring sites within the Environment Canterbury air quality monitoring network. Measurements in Christchurch date back to 1988 and continuous SO2 monitoring have also been carried out in Timaru since 1997. Summary data for SO2 monitoring sites in the Canterbury region are shown in Table 4.4.
Table 4.4: Summary data for SO2 monitoring in Canterbury
View summary data for SO2 monitoring in Canterbury (large table)
4.4.1 Christchurch
Concentrations of SO2 have been measured in central Christchurch since 1988. Figure 4.3 shows that in central Christchurch concentrations of SO2 are typically 'excellent' or 'good'. Higher concentrations have been measured in other more industrial areas of the city (Figure 4.4). The maximum one-hour and 24-hour average concentrations recorded in Hornby are 334 and 104 µgm-3 respectively. In Opawa maximum concentrations for the same averaging periods were 298 and 63 µgm-3.
Figure 4.3: Percentage of measured one-hour and 24-hour average SO2 concentrations within air quality categories at Packe Street and Coles Place in central Christchurch
See figure 4.3 at its full size (including
text description).
Figure 4.4: Percentage of measured one-hour and 24-hour average SO2 concentrations within air quality categories in Hornby and Opawa, Christchurch
See figure 4.4 at its full size (including
text description).
4.4.2 Timaru
Concentrations of SO2 have been monitored at the Timaru monitoring site since 1997. Figure 4.5 shows concentrations are well within the guideline values, with the majority of measurements falling within the 'excellent' air quality category.
Figure 4.5: Percentage of measured one-hour and 24-hour average SO2 concentrations within air quality categories in Timaru
See
figure 4.5 at its full size (including text description).
4.4.3 Ashburton, Rangiora and Kaiapoi
Concentrations of SO2 that were measured in Ashburton, Rangiora and Kaiapoi from 1999 to 2001 were all within the 'excellent' air quality category (Figure 4.6).
Figure 4.6: Percentage of measured one-hour and 24-hour average SO2 concentrations within air quality categories in Ashburton, Rangiora and Kaiapoi
See figure 4.6 at its full size (including
text description).
4.5 West Coast
Continuous monitoring for SO2 was carried out on the West Coast during 2001 at Greymouth. Figure 4.7 shows concentrations were within the 'excellent' or 'good' air quality categories for the duration of the monitoring period.
Figure 4.7: Percentage of measured one-hour and 24-hour average SO2 concentrations within air quality categories in Greymouth, 2001
See figure 4.7 at its full size (including
text description).4.6 Otago region
Measurements of SO2 concentrations in Dunedin are limited to a small number of 24-hour samples measured using wet chemical methods. Table 4.5 shows the results of this monitoring, which was carried out from 1997 to 2000. No graphical analysis was applied to the data owing to the limited number of samples. Results suggest that on the days monitored, SO2 concentrations were much less than the 24-hour average SO2 guideline value. Note, however, that the measurement method used does not comply with existing recommended monitoring methods and is likely to be indicative only.
Table 4.5: Concentrations of SO2 measured in Dunedin (wet chemical)
View concentrations of SO2 measured in Dunedin (wet chemical) (large table)
4.7 Northland region
In the Northland region, monitoring of SO2 has been carried out at Takahiwai between January 1994 and July 2000. The Takahiwai site is generally representative of rural conditions, however a petroleum refinery - a significant source of sulphur dioxide - is situated approximately 4 km due east of the analyser. Most elevated results at this site occur during easterly winds when emissions from the refinery impact upon the analyser.
Figure 4.8: Maximum monthly one-hour average SO2 (µg/m3) concentrations recorded at the Takahiwai monitoring site
See figure 4.8 at its full size (including
text description).
Air quality in this area can be described as 'good' or 'excellent', however, there are occasions when SO2 concentrations have reached the 'alert' category, for example a short period in September 1996. Other peak measurements recorded 1996, 1997, and 1998 (ranging between 130-150 µg/m3) have put the air quality in the 'acceptable' category.
4.8 Summary of SO2 concentrations
Air quality monitoring for SO2 in New Zealand is largely limited to monitoring carried out in Canterbury, the long-term monitoring site in Penrose (ACI), Auckland and around some industrial sources. Data for Christchurch shows some areas of the city where SO2 concentrations have reached the 'acceptable' or 'alert' categories. However, there have been no guideline value exceedences for the one-hour average or 24-hour average from 1992-2001. In other areas of Canterbury, concentrations are typically 'excellent'. In Auckland (Penrose) and around some industrial sites, one-hour average SO2 concentrations reached the 'alert' category. The limited amount of SO2 monitoring that has been carried out in other parts of New Zealand does not indicate concentrations of concern.
