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6 Sources of ozone precursors

Ground level ozone is a secondary pollutant, which is formed when the primary pollutants nitrogen oxides (NOx) and volatile organic compounds (VOC) combine in the presence of sunlight (MfE, 1994). The main VOC of interest are those with eight or less carbon atoms per molecule as these are the most reactive in the atmosphere. The exception is methane, which has one carbon atom and is relatively stable. Because sources of nitrogen oxide are considered in Section four, the focus of this section is on emissions of VOC.

Not all inventories have included estimates of VOC. Of those that have, not all specify that emission estimates have been for non-methane VOC. However, it has been assumed that unless specified, estimates of VOC in the inventories refer to non-methane VOC.

Figures 6.1 to 6.7 show the relative contribution of different sources to VOC emissions in different areas of New Zealand. In most areas, domestic home heating and motor vehicles are estimated to be the main contributors to VOC emissions. In Gisborne, natural emissions are the dominant source of VOC emissions. However, in most other areas natural source emissions were not included in the emission inventory assessment. Consequently, this source may also be a significant contributor in other areas. An estimate of natural VOC emissions for New Zealand has been made (NIWA, 1996). These results cannot easily be extended to the existing inventories because of differences in the spatial resolutions.

In Taupo, Christchurch and Kaiapoi, industry is a significant contributor to VOC emissions. Table 6.1 shows summary data for VOC emissions for different areas of New Zealand.

Figure 6.1: Sources of VOC in Wellington (1999 inventory) and Auckland (1993 inventory)

Figure 6.2: Sources of VOC in Northland (non-specific year) and Gisborne (1996 inventory)

Figure 6.3: Sources of VOC in Taupo and Tokoroa (2001 inventory)

Figure 6.4: Sources of VOC in Hamilton (2001 inventory) and Christchurch

Figure 6.5: Sources of VOC in Taranaki (1998 inventory)

Figure 6.6: Sources of VOC in Rangiora, Kaiapoi, Ashburton and Waimate

 

Figure 6.7: Sources of VOC in Nelson (2001 inventory) and Richmond (2000 inventory)

Table 6.1: Comparison of VOC emission estimates for different regions of New Zealand


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

Christchurch

20,303

1,525

11,634

  

33,461

Rangiora

976

322

19

  

1,317

Kaiapoi

579

380

1,727

  

2,686

Ashburton

1,336

634

37

  

2,007

Waimate

474

44

2

  

521

Timaru

-

-

-

  

-

Nelson

4,120

29

1,581

692

 

6,423

Northland

6,929

6,784

1,509

318

 

15,540

Auckland

60,900

106,000

11,000

29300

2100

209,300

Hamilton

7,131

7,952

3

  

15,086

Taupo

1,232

476,100

809

  

478,141

Tokoroa

1,883

898

39

  

2,820

 

Domestic/ commercial heating 
kg/day

Motor vehicles
kg/day

Industry
kg/day

Other domestic
kg/day

Other mobile 
kg/day

Total
kg/day

Wellington

94,600

81,200

16,800

2,500

4,800

199,900

 

Domestic 
t/ year

Mobile sources
t/ year

Industry
t/ year

Burn-offs
t/ year

 

Total 
t/ year

Taranaki

868

2,358

237

  

3,463

Gisborne

838

787

50

296

 

1,971