View all publications

3 Carbon monoxide (CO) emissions

3.1 Auckland

Motor vehicles contribute the majority of the CO emissions in Auckland, with the 1993 inventory indicating that around 84% are likely to be attributable to this source overall (Figure 3.1). In any location however, the relative contribution from different sources will depend on factors such as proximity to roadways. For example, monitoring in areas such as Queen Street or Khyber Pass Road is likely to represent an even greater proportion of motor vehicle emissions.

Figure 3.1: Sources of CO in Auckland (1993 inventory)

3.2 Wellington

The main source of carbon monoxide in Wellington is motor vehicle emissions, with the 1998 inventory indicating that around 64% of emissions were from this source. The other significant source of carbon monoxide is domestic and commercial combustion, which contributes around 26% of the CO emissions. These results are estimates of the relative contribution of each source averaged across the whole of the Wellington region, including both urban and rural areas.

Figure 3.2: Sources of CO in Wellington (1998 inventory)

 

3.3 Waikato Urban Areas

In Hamilton, motor vehicle emissions and domestic home heating each contribute around half of the CO emissions (Figure 3.3). Because of the very low presence of industry in the area, this source contributes less than 1% of the CO emissions. Figure 3.4 shows the relative contribution of different sources to CO emissions in Taupo and Tokoroa. In Taupo, motor vehicle emissions are the main source of CO contributing around 68%. The main source of CO in Tokoroa is domestic home heating, with motor vehicles contributing around 26% and industry around 11%. The latter contribution excludes Kinleith Pulp and Paper, which is located approximately 5 km from the Tokoroa township.

Figure 3.3: Sources of CO in Hamilton (2001 inventory)

 

Figure 3.4: Sources of CO in Taupo and Tokoroa (2001 inventory)

 

3.4 Taranaki, Northland, Gisborne and Bay of Plenty

The main source of carbon monoxide in Taranaki is motor vehicle emissions. Figure 3.5 shows around 71% of the CO emissions in Taranaki are from this source, with domestic heating contributing around 19% and industry 10%. The majority of the CO emissions in Taranaki occur within the New Plymouth Bell Block Urban and the Remaining Pastoral Land (Figure 3.5).

In Northland, motor vehicles contribute around half of the CO emissions with domestic fires contributing 38% and industry 8% (Figure 3.6). Motor vehicle emissions are also the main contributor in Gisborne, although less significant at 43%. Of interest is the contribution of natural sources (19%), as this source is not included in most inventories. In the Bay of Plenty, motor vehicle emissions comprise about half of the CO, with one quarter from domestic heating and the remainder industry and agriculture (Figure 3.7). The majority of the CO emissions occur within the areas of Rotorua and Tauranga.

Unlike inventories for other areas, relative contributions to emissions in Taranaki, Northland, Gisborne and Bay of Plenty are based on annual averages, rather than winter specific data. The relative contribution from the domestic heating sector may therefore be higher during the winter months.

Figure 3.5: Sources of CO in Taranaki (left) and the proportion of CO from different areas within Taranaki (right)

 

Figure 3.6: Sources of CO in Northland (non-specific year) and Gisborne (1996 inventory)

 

Figure 3.7: Sources of CO in Bay of Plenty (left) and the proportion of CO from different areas within the Bay of Plenty region (right)

 

3.5 Canterbury

The main urban centres in Canterbury are Christchurch and Timaru. In Christchurch, about half of the CO emissions come from motor vehicles with 46% from domestic heating and 1% from industry. Motor vehicles are less dominant in Timaru, contributing about one-third of the CO emissions. Domestic home heating is the main source of CO emissions in Timaru (Figure 3.8).

Figure 3.8: Sources of CO in Christchurch (1999 inventory) and Timaru (2001 inventory)

 

In the smaller urban centres of Rangiora, Kaiapoi, Ashburton and Waimate, domestic heating and motor vehicles are the main contributors to CO emissions (Figure 3.9). The contribution of each source is about 50% in Rangiora, Kaiapoi and Ashburton. In Waimate domestic heating contributes 83% of the CO emissions.

Figure 3.9: Sources of CO in Rangiora, Kaiapoi, Ashburton and Waimate

 

3.6 Otago

The main sources of CO in Dunedin and the urban centres of Otago are motor vehicle emissions and domestic home heating (Figure 3.10), with industry contributing around 3%. Some variations do occur with location (Figure 3.11), with motor vehicles contributing a low of 9% in Arrowtown and up to 45% in Dunedin. With the exception of Balclutha, where motor vehicles contribute 44% of the CO emissions, domestic heating is the main source of CO in the urban centres of Otago, as shown in Figures 3.11 and 3.13.

Figure 3.10: Sources of CO in Dunedin and for the urban areas in Otago (1999 inventory)

 

Figure 3.11: Sources of CO in Alexandra, Arrowtown, Balclutha and Clyde (1999 inventory)

 

Figure 3.12: Sources of CO in Cromwell, Milton, Mosgiel and Oamaru (1999 inventory)

 

Figure 3.13: Sources of CO in Queenstown and Wanaka (1999 inventory)

 

3.7 Nelson and Richmond

The main sources of CO emissions in both Nelson and Richmond are motor vehicles and domestic fires, with each contributing around half in Nelson and domestic heating being slightly more dominant in Richmond at 63% (Figure 3.14). Minor sources in both areas include outdoor burning and industry.

Figure 3.14: Sources of CO in Nelson (2001 inventory) and Richmond (2000 inventory)

 

3.8 Trends in CO emissions in New Zealand

Motor vehicle emissions and domestic heating are the main sources of CO in most urban areas of New Zealand. Some trends in CO emissions from motor vehicles can be assessed based on the estimated impacts of changes in vehicle technology and fuels. The New Zealand Transport Emission Rate model (NZTER) produced by the Ministry of Transport as a part of the vehicle fleet emission control strategy indicates a reduction in carbon monoxide emissions from this source with time. The reductions are primarily associated with improved vehicle technology and are illustrated in Figure 3.15. The three levels of service (LOS) categories represent emission rates for different levels of congestion.

Changes in home heating methods will also influence trends in CO emissions in most areas. These changes are likely to be area specific, although factors such as increases in electricity prices or concerns regarding supply could have nationwide implications. Increases in the numbers of burners will increase CO emissions, however, in some areas these increases may be offset by the replacement of older burners and open fires with lower emission wood burners.

Figure 3.15: Predicted trends in CO emissions from motor vehicles

 

In a number of areas of New Zealand management measures are being proposed or implemented to reduce PM10 emissions from domestic home heating. It is likely that these measures will also result in a reduction in CO emissions from this source.

Only a small number of inventories have been conducted for a second time. In particular, an assessment has been carried out for Timaru, comparing 1996 and 2000, and for Christchurch, comparing 1996 and 1999. The latter area shows some changes in home heating methods, with an increase in the number of households using solid fuel burning and a decrease in the use of coal. While the impact of these changes on PM10 emissions is minimal, an increase in CO emissions of around 10% is estimated after adjustments for changes in methodology have been made. No significant changes in home heating trends or emissions were apparent in the 1996 and 2000 Timaru emission inventory comparison.

3.9 Summary of sources of CO in New Zealand

The main sources of CO emissions in most urban areas of New Zealand are motor vehicle emissions and domestic home heating. Emission inventories suggest that these are approximately equal contributors in many urban areas, although vehicle emissions are the dominant source in Auckland, Wellington, Taranaki and Taupo.

Table 3.1 shows estimates of CO discharges to air from different sources in kilograms per day and tonnes per year. With the exception of Bay of Plenty, Taranaki and Gisborne, this data represents the average wintertime emission sources.

For the larger cities, CO emissions of around 150 to 1000 tonnes per day are estimated, compared to around 30 tonnes or less for most of the smaller urban areas. In Auckland, over 1000 tonnes of CO is emitted per day during the winter compared to around 150 tonnes for Christchurch and 180 tonnes for Wellington.

The relative contributions to CO emissions shown in table 3.1 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. Further discussion on the limitations of different inventories is contained in Table 2.1.

Table 3.1: Comparison of CO emission estimates for different regions of New Zealand

 

Domestic 
kg/day
Mobile sources 
kg/day

Industry
kg/day

    Total
kg/day

Alexandra

1,596

708

81

   

2,385

Arrowtown

838

85

10

   

933

Balclutha

880

708

17

   

1,605

Clyde

348

44

8

   

400

Cromwell

786

174

28

   

988

Milton

796

241

33

   

1,070

Mosgiel

1,965

557

210

   

2,732

Oamaru

6,193

3,150

178

   

9,521

Queenstown

4,401

2,338

100

   

6,839

Wanaka

1,096

285

49

   

1,430

Dunedin

20,215

17,416

1,173

   

38,804

  Domestic heating 
kg/day
Motor vehicles
kg/day
Industrykg/day Other domestickg/day Other mobile
kg/day
Total 
kg/day

Christchurch

70,220

80,269

1,066

   

151,555

Rangiora

2,316

2,437

6

   

4,759

Kaiapoi

2,316

2,929

3

   

5,248

Ashburton

5,345

4,780

44

   

10,169

Waimate

1,898

371

3

   

2,272

Timaru

9,991

6,088

33

   

16,112

Nelson

14,053

12,378

438

284

 

27,152

Northland

30,074

41,556

6,006

1,510

 

79,146

Auckland

140,200

883,000

3,500

19,900

6,900

1,053,500

Hamilton

32,605

34,111

3

   

66,719

Taupo

3,235

8,011.078

496

   

11,742

Tokaroa

7,533

3,098.58

1,297

   

11,928

  Domestic/ commercial heating 
kg/day
Motor vehicles
kg/day
Industry
kg/day
Other domestic
kg/day
Other mobile
kg/day
Total 
kg/day

Wellington

47,720

115,400

3,500

3,050

7,630

177,300

  Domestic
t/ year
Mobile sources 
t/ year
Industry
t/ year
Burn-offs 
t/ year
  Total
t/ year

Taranaki

3,467

13,257

1,769

   

18,493

BOP

7,991

16,848

5,687

2,661

 

33,187

Gisborne

1,505

2,877

175

831

 

5,388