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5 Sulphur dioxide (SO2) emissions

5.1 Auckland

The main source of SO2 emissions in Auckland, as indicated by the 1993 inventory, is industry. This source contributes 56% of the SO2 emissions compared to 14% from motor vehicles, 10% from other mobile sources and 20% from domestic sources (Figure 3.1). This represents the average contribution across the whole of the city. The industrial component is therefore likely to be higher nearer industrial areas and lower in residential areas located further away from industry.

Figure 5.1: Sources of SO2 in Auckland (1993 inventory)

5.2 Wellington

The main source of SO2 in the Wellington region is commercial shipping, which comprises the majority of the other mobile sources category in Figure 5.2. This source accounts for around 82% of the SO2 emissions in the Wellington region. In areas distant from the harbour, motor vehicles, industry and domestic heating are more likely to contribute to SO2 emissions.

Figure 5.2: Sources of SO2 in Wellington (1998 inventory)

5.3 Waikato Urban Areas

The main source of SO2 in Hamilton is motor vehicle emissions, which contribute 66% of the SO2 emissions. In Tokoroa, industry contributes 41%, with motor vehicles and domestic home heating contributing about 30% each (Figure 5.3). These estimates exclude emissions from Kinleith as this is located 5 km outside of the Tokoroa township. When the wind is directing emissions from Kinleith to Tokoroa, the contribution to SO2 emissions from industry will increase. In Taupo, motor vehicles are the major contributor to SO2 emissions contributing 77% (Figure 5.4).

Figure 5.3: Sources of SO2 in Hamilton and Tokoroa (2001 inventory)

Figure 5.4: Sources of SO2 in Taupo (2001 inventory)

5.4 Northland, Gisborne and Bay of Plenty

The main source of SO2 emissions in Northland is industry, contributing 96% of emissions. In Northland these emissions are dominated by the petroleum industry, which contributes 90% of the industry SO2 emissions. In Gisborne, transport is the main source of SO2 contributing 89%. Area sources including domestic home heating contribute the remainder of the SO2 emissions in Gisborne (Figure 5.5).

Figure 5.5: Sources of SO2 in Northland (non-specific year) and Gisborne (1996 inventory)

Figure 5.6: Sources of SO2 in Bay of Plenty (left) and the proportion of SO2 from different areas within the Bay of Plenty region (right)

5.5 Canterbury2

The main source of SO2 in Christchurch and Timaru is industry, which contributes 80% in Christchurch and 56% in Timaru (Figure 5.7). In Christchurch, the main industrial source of SO2 emissions is coal-fired boilers, which comprise 60% of the industrial component. A fertiliser works is the main single source of SO2 emissions in Christchurch, contributing 30% of the industrial component. Secondary sources of SO2 emissions in Timaru include motor vehicles and industry, contributing 26% and 18% respectively. In Christchurch, motor vehicles and domestic heating contribute less, at 14% and 6% respectively. Domestic heating and motor vehicles contribute a greater proportion of SO2 emissions in the smaller urban areas of the region (Figure 5.8).

Figure 5.7: Sources of SO2 in Christchurch (1999 inventory) and Timaru (2001 inventory)

Figure 5.8: Sources of SO2 emissions in Rangiora, Kaiapoi, Ashburton and Waimate

5.6 Otago

Industry is the dominant source of SO2 emissions in Dunedin, contributing 89% of the emissions (Figure 5.9). Industry is also a major contributor in many of the smaller areas of the region, although the proportion of emissions from domestic heating often increases in these areas (Figures 5.10–5.12); this typically occurs because many of the smaller urban areas have limited industrial contributions.

Figure 5.9: Sources of SO2 in Dunedin (1999 inventory)

Figure 5.10: Sources of SO2 in Alexandra, Balclutha, Arrowtown and Clyde (1999 inventory)

Figure 5.11: Sources of SO2 in Cromwell, Mosgiel, Milton and Oamaru (1999 inventory)

Figure 5.12: Sources of SO2 in Queenstown and Wanaka (1999 inventory)

5.7 Nelson and Richmond

Industry is the main contributor to SO2 emissions in both Nelson and Richmond (Figure 5.13), contributing 75% and 85% in these areas respectively. The main industrial sources of SO2 in Nelson and Richmond are coal-fired boilers, which contribute 71% and 64% in these areas respectively.

Figure 5.13: Sources of SO2 in Nelson (2001 inventory) and Richmond (2000 inventory)

5.8 Trends in SO2 emissions in New Zealand2

The main source of SO2 emissions in many urban areas of New Zealand is industry. However, motor vehicles are the dominant contributor in most areas where industry emissions are minimal. SO2 emissions from motor vehicles are dominated by emissions from diesel vehicles. Changes in emissions from motor vehicles and industry will therefore be key drivers in trends in SO2 concentrations within urban areas of New Zealand.

For motor vehicle emissions, factors such as increasing use of diesel vehicles and revisions to the fuel specifications will impact on SO2 emissions. The 2001 Ministry of Economic Development review of the fuel specifications for petroleum products in New Zealand includes a reduction in maximum sulphur content of petrol vehicles from 500 ppm to 50 ppm.

Figure 5.14 shows an estimate of the changes in SO2 emissions from motor vehicles with time as estimated by the Fuel and Energy Group for Environment Canterbury in 2001. The three levels of service (LOS) categories represent emission rates for different levels of congestion.

Figure 5.14: Predicted trends in SO2 emissions from motor vehicles

Future trends in SOx emissions from industry are difficult to assess. In many areas, these are likely to be dominated by coal-fired boilers with some contribution from diesel boilers. Growth in industry is likely to be area specific and may depend on the extent of existing regulation control measures.

There is very limited trend information from emission inventory studies as Timaru and Christchurch are the only areas to have published a second inventory assessment. The Timaru inventory shows no changes in total SOx emissions from 1996 to 2000. A comparison of 1996 and 1999 SO2 emission estimates for Christchurch shows a significant increase in SO2 between the two inventories. However, methodological differences in the assessment of emissions from this source are likely to account for much of this difference.

5.9 Summary of Sources of SO2 in New Zealand

The results of the emission inventory investigations into sources of SOx in New Zealand are shown in Table 5.1. With the exception of Bay of Plenty, Taranaki and Gisborne, this data represents average wintertime emission sources.

In Northland, around 14 tonnes of SOx is estimated compared to around 8 tonnes in Christchurch and 7 tonnes in Auckland and Wellington. Unlike the other larger cities, which are dominated by industry, commercial shipping produces the majority of the SO2 emissions in Wellington.

The relative contributions to SOx emissions shown in Table 5.1 are based on assumptions relating to emission rates and fuel use and contain some degree of uncertainty. There is some variation from area to area in the approach taken and the subsequent confidence in the results. Some limitations associated with different emission inventory assessments are discussed in Table 2.1.

Table 5.1: Comparison of SO2 emission estimates for different regions of New Zealand

Domestic
kg/day
Mobile sources 
kg/day
Industry 
kg/day
Other domestic
kg/day
Other mobile
kg/day
Total 
kg/day

Alexandra

59

4

162

   

225

Arrowtown

16

0.5

26

   

43

Balclutha

99

5

60

   

164

Clyde

14

0.5

11

   

26

Cromwell

23

1

62

   

86

Milton

52

2

153

   

207

Mosgiel

64

6

437

   

507

Oamaru

75

20

543

   

638

Queenstown

35

53

252

   

340

Wanaka

8

2

97

   

107

Dunedin

435

153

5,108

   

5,696

 

Domestic heating 
kg/day

Motor vehicles
kg/day

Industry
kg/day

Other domestic 
kg/day

Other mobile
kg/day

Total 
kg/day

Christchurch

463

1,113

6,613

   

8,189

Rangiora

52

40

43

   

135

Kaiapoi

44

64

21

   

129

Ashburton

214

84

199

   

497

Waimate

45

6

21

   

72

Timaru

55

89

176

   

320

Nelson

45

138

549

3

 

736

Northland

72

447

13,301

6

 

13,826

Auckland

400

1,000

4,000

1,010

710

7,120

Hamilton

223

425

2

   

650

Taupo

16

75

7

   

98

Tokoroa

49

51

72

   

172

 

Domestic/ commercial heating 
kg/day

Motor vehicles 
kg/day

Industry
kg/day

Other domestic
kg/day

Other mobile
kg/day

Total
kg/day

Wellington

150

900

300

10

6,020

7,380

 

Domestic
t/ year

Mobile sources
t/ year

Industry
t/ year

Burn-offs
t/ year

 

Total
t/ year

BOP

243

1,167

646

   

2,056

Gisborne

6

47

0.18

   

53