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2 Emission inventories in New Zealand

A number of emission inventories have been carried out primarily in the urban areas of New Zealand since 1995. These typically include detailed assessments of PM10 or TSP emissions from domestic heating, motor vehicles and industry, although emission estimates for a number of minor PM10 sources are also included in some of the studies. Some of the later inventories also include estimates for the PM2.5 size fraction, although there is generally increased uncertainty surrounding the emission factors for this size fraction.

Emission estimates for PM10 are typically presented as daily average wintertime rates, as it is during this season that PM10 concentrations in most areas of New Zealand are elevated. Some inventories, in particular those employing the simpler screening type methodologies only produce annual emission estimates (Table 2.1). This report summarises the results of the emission inventories carried out in New Zealand to date for TSP, PM10 and PM2.5, where available.

Table 2.1: Summary of the most recent emission inventories for New Zealand

Location Year Sources Contaminants Output Methodology

Auckland

1993

Transport, area, vegetation, industry

Particles, CO, NOx, SO2

t/day

Grid square, wide range of sources, detailed data collection

Wellington

1998

Transport, industry, biogenic, domestic heating, burning and lawn mowing

PM10, NOx, CO, CO2, SO2, NMVOC

t/day

Grid square, wide range of sources, detailed data collection

Christchurch

1999

Motor vehicles, domestic heating, industry

PM10, NOx, CO, CO2, SO2,

kg/day

Limited spatial resolution, comprehensive data collection for major sources only

Timaru

2001

Motor vehicles, domestic heating, industry

PM2.5, CO, NOx, benzene, BaP, dioxin, SO2

kg/day

Comprehensive data collection for major sources only

Dunedin and 10 ORC urban areas

1999

Transport, domestic heating, industry

PM10, NOx, CO, SO2

kg/day

Detailed data collection for most sources, some limitations in motor vehicle emissions assessment

Hamilton, Tokoroa, Te Kuiti, Taupo

2001

Transport, domestic heating, industry

PM10, CO, NOx, SOx, VOC, CO2

kg/day

Detailed data collection, reliant on 1997 industry assessment

Nelson

2001

Motor vehicles, domestic heating, industry, outdoor burning

PM2.5, CO, VOC, NOx, benzene, SO2

kg/day

Comprehensive data collection for major sources only

Richmond

2000

Motor vehicles, domestic heating, industry, outdoor burning

PM2.5, CO, VOC, NOx, benzene, SO2

kg/day

Detailed data collection for most sources, some limitations in motor vehicle and outdoor burning emissions assessment

Gisborne

1996

Transport, area, industrial, agricultural, natural

TSP, SOx, NOx, VOC, CO, CO2

t/year

Screening approach to major sources, high potential for error

Bay of Plenty

1997

Transport, industry, domestic, pollen, agriculture, geothermal

TSP, SO2, CO, NOx, H2S, dioxins

t/year

Screening approach to major sources, high potential for error

Northland

Non-specific

Motor vehicles, domestic heating, industry, agriculture

PM10, CO, NOx, SOx, NMVOC, CO2, N2O, CH4

t/year

Detailed data collection for most sources, some screening methods used

Taranaki

1998

Motor vehicles, domestic heating, industry, farm animals, vegetation

PM2.5, CO, NOx, VOC, BaP, CH4, N2O, NMHC

t/year

Screening approach to major sources, high potential for error

2.1 Auckland

The Victorian Environmental Protection Agency (EPA) in collaboration with NIWA carried out the first emission inventory assessment for Auckland in 1995. The Auckland Regional Council initiated a review and information update for this inventory for the year 1998, however these updates are not yet available owing to concerns with some of the existing source and emissions information.

The 1995 Auckland emission inventory is comprehensive in its inclusion of sources and in its spatial distribution of the emission estimates from these sources. Table 2.2 shows the range of sources included. The spatial resolution for the inventory is an 87 km by 99 km grid, which contains in excess of 8600 km2 divided into 957 grid cells each 3 km by 3 km.

Table 2.2: Sources included in the 1995 Auckland emission inventory

Motor vehicles Domestic and area sources Industry Biogenic sources
  • Motor vehicles (exhaust and evaporative)
  • Marine pleasure craft/ shipping
  • Rail
  • Aviation
  • Surface coating and thinners
  • Aerosols
  • Service stations/ refuelling
  • Fuel combustion
  • Lawn mowing
  • Cutback bitumen
  • Natural gas leakage
  • Off road vehicles
  • Dry cleaning
  • Domestic waste combustion
  • Other unaccounted for industrial/commercial emissions
  • Food manufacture
  • Mining and quarrying
  • Wood and paper products
  • Chemical manufacture
  • Textiles
  • Non-metallic minerals
  • Metal manufacture
  • Can coating
  • Fabricated metals
  • Printing
  • Power generation
  • Miscellaneous industries
  • Fuel storage
  • Vegetation
  • Soil

 

The relative contributions of different sources to PM10 emissions across the whole of the study area from the 1995 inventory are shown in Figure 2.1. However, some concerns have been raised about the quality of some of the input data and thus the accuracy of the emissions estimates. Attempts to resolve these issues for the 1998 inventory are a current priority for the Auckland Regional Council.

Figure 2.1: Relative daily (wintertime) contribution of sources to TSP emissions in the Auckland region

The main sources of industrial TSP emissions in the Auckland region are metal manufacture and the non-metallic minerals industry, which contribute 45% and 18% of the industrial emissions respectively.

In addition to the emission inventory assessments, the Auckland Regional Council propose to identify the relative contributions of different sources to PM10 concentrations based on receptor modelling methodologies. Receptor modelling involves identifying the elemental composition of particles and uses statistical methods to identify sources based on the prevalence of different ratios of elements. Monitoring for this work is scheduled to commence during 2003.

2.2 Waikato region - Hamilton, Tokoroa and Te Kuiti and Taupo

An assessment of sources of PM10 and other contaminants in Hamilton, Tokoroa and Te Kuiti was carried out during 1997 using emission inventory methodology. The inventory was carried out in two phases: the assessment of emissions from domestic heating and motor vehicles and the assessment of emissions from industry. Results from these phases were not combined for 1997 to give an overall assessment for these areas.

An assessment of emissions from home heating was carried out for the areas of Huntly, Matamata and Putaruru during 2000. In Taupo, both domestic heating and motor vehicle emissions were assessed for 2000. Industry information from 1997 were used to estimate the industry contribution to PM10 emissions in Taupo. Figure 2.2 shows the estimated relative contributions to PM10 emissions in Taupo. However, an assessment of PM10 sources in Taupo suggests that the industrial emissions component may be overestimated because of the uncertainties surrounding emission factors associated with emissions from a local wood-panelling site (Wilton, 2002a).

Figure 2.2: Relative contributions to wintertime PM10 emissions in Taupo in 2000

In 2001, emissions from domestic heating were reassessed for Hamilton, Tokoroa and Te Kuiti and also for motor vehicles in Hamilton. The latter data were combined with 1997 industrial emission estimates to provide an assessment of the relative contribution of domestic heating, motor vehicles and industry to PM10 emissions in Hamilton. Figure 2.3 shows the relative contribution of these sources to PM10 emissions in Hamilton and Tokoroa. The Tokoroa emission estimates exclude emissions from Kinleith, a major industrial source of emissions located about 5 kilometres from the township.

Figure 2.3: Relative contributions to wintertime PM10 emissions in Hamilton and Tokoroa

2.3 Bay of Plenty

An emission inventory encompassing the whole of the Bay of Plenty region was carried out in 1997. It is difficult to compare the results of this emission inventory with inventories from other regions in New Zealand as the inventory design and presentation precludes an assessment of daily PM10 emission estimates by source for the urban centres.

The focus of the Bay of Plenty inventory is on annual emission estimates for CO, SO2, NOx and particles, which is referred to as PM and is an estimate of total suspended particles. A range of sources including on-road and marine transportation, industrial and commercial activities, domestic activities, agricultural and forestry and geothermal sources were included in the inventory. The presentation of results for particles is limited to the categories, industrial, residential/commercial, transport and burn-offs.

The inventory includes a breakdown of total emission estimates for particles for the districts Western BOP, Tauranga, Whakatane, Kawerau and Rotorua and by urban centre for Tauranga, Rotorua and Whakatane. Figure 2.4 shows the estimated annual contribution of each source to particle emissions for the whole region and a breakdown of the emissions by district.

Figure 2.4: Relative contribution to annual particle emissions in the Bay of Plenty by source and area for 1997

Although no data are provided, the report does indicate that the relative contribution of the residential and commercial sector to PM emissions does increase to 55% if just the winter data are included (Weymss, 1997). However, the methodology used in the inventory to estimate emissions from domestic home heating relies heavily on home heating methods and fuel use in other areas such as Auckland and Christchurch and results should therefore be treated with caution.

2.4 Taranaki

An emission inventory for the Taranaki region was carried out during 1998. The methodology was similar to the Bay of Plenty region in that results were presented as annual emission estimates. However, the study included both PM10 and PM2.5 size fractions and incorporated more appropriate methods of assessing domestic heating emissions. Other contaminants assessed in the inventory included CO, methane (NH4), non-methane hydrocarbons (NMHC), VOCs, nitrous oxide (N2O), nitric oxide (NO) and nitrogen dioxide (NO2).

Results were presented for the Taranaki region as a whole and broken down into areas representing different land uses. Figures 2.5 and 2.6 show the relative contribution of different sources to PM10 and PM2.5 emissions for Taranaki and the distribution of these emissions across the different areas.

Figure 2.5: Relative contribution to annual PM10 and PM2.5 emissions in Taranaki for 1998

Figure 2.6: Distribution of annual PM10 and PM2.5 emissions within Taranaki for 1998

2.5 Wellington

The Wellington emission inventory was carried out for the year 1998 and included three separate reports quantifying emission estimates from domestic and commercial sources, industrial and mobile sources and biogenic sources. Contaminants included were, PM10, CO, NOx, SOx, NMVOC and CO2.

The PM10 emissions sources included in the inventory were:

  • fuel combustion (domestic and commercial)
  • domestic waste burning
  • lawn mowers
  • marine craft
  • farm-based mobile sources
  • rural burn-off
  • industry
  • motor vehicles
  • aviation.

Results for each of the inventory phases were presented as average summer and winter's day emissions for the whole region, although data were collected at a more detailed spatial distribution. Figure 2.7 shows the relative contribution to PM10 emissions for the Wellington region for the average winter's day.

Figure 2.7: Relative contribution to wintertime PM10 emissions in Wellington

Although domestic and commercial combustion is the dominant source of PM10 emissions, around 20% arise from industrial processes. The main contributor to industrial PM10 emissions in Wellington is mining and quarrying, which is estimated to produce 60% of the industrial PM10 emissions. The other main contributor is the wood products industry, which is responsible for around 25% of the industrial PM10 emissions.

2.6 Canterbury region

Emission inventories have been carried out in six of the urban towns within the Canterbury region. Emission inventories for Christchurch have been carried out during 1996 and 1999 and a third inventory for Christchurch for 2002 is currently being prepared. In Timaru inventories have been carried out for 1996 and 2001 and in Ashburton, Kaiapoi and Waimate emissions were assessed during 1997.

The Canterbury inventories focus on emissions from domestic fires, motor vehicles and industrial sources, although a number of other sources of PM10 are considered in the Timaru 2001 inventory.

2.6.1 Timaru

The 2001 Timaru emission inventory was primarily designed to examine sources of PM10, although emission estimates for CO, NOx, SOx, CO2, benzene, dioxins, benzo(a)pyrene and PM2.5 were also made. The inventory encompassed the urban areas of Timaru with a further spatial breakdown provided for the following census area units:

  • Washdyke
  • Waimataitai (Māori Park and Waimataitai)
  • Marchwiel
  • Gleniti (Gleniti and Glenwood)
  • Highfield
  • Fraser Park
  • Seaview
  • Watlington
  • Parkfield
  • Kensington (Redruth and Timaru Gardens).

Results of the 2001 Timaru emission inventory indicate that solid fuel burning for domestic home heating is the main source of PM10 emissions in the area (Figure 2.8). Although not included in Figure 2.8, estimates of PM10 emissions from rail transport, dust from tilling, lawn mowers, leaf blowers and chainsaws, brakes and tyres, marine activities and cigarette smoke were also considered. They were not included in the total emissions assessment as uncertainties surrounding most of these estimates were high. However, the overall contribution of these sources was minimal at less than 50 kg/day compared to the domestic heating contribution of 1124 kg/day. Outdoor burning is prohibited in Timaru in urban areas so was not included in the assessment.

The inclusion of emission estimates for PM2.5 in the Timaru 2001 inventory also provides a useful indication of the contribution of different sources to this size fraction. These data indicate that around 90% of domestic home heating emissions are in the PM2.5 size fraction compared to around 60% for motor vehicles and 50% for industry. However, the 2001 inventory cautions on the use of these data as the emission factors for this size fraction are less certain and should be treated as indicative only (Wilton, 2001c).

The 2001 Timaru inventory also included an assessment of trends in sources of PM10 emissions since the 1996 inventory survey. After adjusting for differences in methodology it appears that PM10 emissions are unlikely to have changed significantly in Timaru between the years 1996 and 2000 (Wilton, 2001c).

Figure 2.8: Relative contributions to wintertime PM10 and PM2.5 emissions in Timaru in 2001

2.6.2 Christchurch

The most recent available emission inventory data for Christchurch is for 1999. The inventory focused on emissions of PM10 during the winter, as it is these months when PM10 concentrations in Christchurch exceed guideline values. Sources included in the assessment were domestic home heating, motor vehicles and industry. No outdoor burning sources were included as this activity is prohibited in Christchurch during the winter months. The Christchurch territorial boundary was used to define the total inventory area and breakdowns for the inner Christchurch area and the 25-suburb area used in the 1996 inventory were included.

Figure 2.9: Relative contribution to wintertime PM10 emissions in the Christchurch 25 suburb area in 1999

Results for the 1999 emission inventory indicate that the majority of the PM10 emissions come from solid fuel burning for domestic home heating. Figure 2.9 shows that for the 25-suburb area, 80% of the PM10 emissions occur as a result emissions of domestic heating with 10% from motor vehicles and 10% from industry. Of these, over half come from open fires and pre 1989 enclosed burners (Figure 2.10). While the overall contribution from domestic heating is similar to the 1996 emission inventory, some changes in the types of heating methods contributing to the domestic heating emissions have occurred. Most notable was a decrease in the contribution from coal burning and a significant increase in the number of enclosed burners.

While no assessment of the relative contribution of different sources during the summer months has been carried out, the prevalence of summer home heating is likely to be minimal. Thus industry and motor vehicles will be more significant contributors at that time of the year. In addition, it is likely that other wind related sources such as dusts and sea spray may increase during the summer months.

Figure 2.10: Relative contribution of different heating methods to domestic heating emissions in Christchurch in 1999

In addition to an assessment of the relative contribution of these sources to PM10 emissions in Christchurch, estimates have been made of the relative contribution of these sources to PM10 concentrations in the city. A difference between contributions to emissions and contributions to concentrations occurs because of variations in the emissions sources with time of day. Table 2.3 (from the 1999 Christchurch emission inventory) shows that the majority of domestic heating emissions occur during the evening time period (6-10 pm). This coincides with the time of the day when meteorological conditions are most conducive to pollution. Consequently, emissions that occur during this period will have a greater impact on concentrations than those that occur during the daytime when higher wind speeds result in greater dispersion.

Table 2.3: Differences in the time of day that emissions from different sources occur

  6-10 am 10 am-4 pm 4-10 pm 10 pm-6 am PM10 (kg)

Domestic heating

668

1479

5720

989

8856

Motor vehicles

328

541

428

65

1361

Industry

237

497

232

214

1180

Total Christchurch

1233

2518

6380

1268

11,397

In Christchurch, the impact of differences in the time of day that emissions from different sources occur can be quantified using a box model developed for Christchurch by NIWA(Gimson and Fisher, 1997). The box model accounts for the impact of meteorology at different times of the day for a typical high pollution night and allows predictions of PM10 concentrations for variations in the timing of emissions. The outputs of the model have been used to weight the emissions from different sources relative to their contribution to 24-hour average PM10 concentrations (Figure 2.11). This model also indicates a linear approach to the relationship between emissions and concentrations.

Figure 2.11: Relative contribution to wintertime PM10 concentrations on nights of high air pollution in Christchurch for 1999

2.6.3 Ashburton, Kaiapoi, Rangiora and Waimate

Emission inventory investigations for Ashburton, Rangiora, Kaiapoi and Waimate were carried out for the year 1997. The main air quality concern in these towns was concentrations of PM10, although estimates of CO, NOx, SOx, VOC and CO2 were also included. Sources targeted included domestic home heating, motor vehicles and industry.

The main source of PM10 emissions in each area was domestic home heating with contributions ranging from 97% in Waimate to 76% in Ashburton (Figure 2.12). Industrial contributions were also significant in Ashburton contributing 22% of the PM10 emissions. In all areas the motor vehicle contribution was minor.

Figure 2.12: Relative contribution to wintertime PM10 emissions in Rangiora, Kaiapoi, Ashburton and Waimate in 1997

2.7 Nelson

The Nelson 2001 emission inventory was primarily designed to examine sources of PM10 during the winter months as PM10 concentrations in Nelson were found to regularly exceed ambient air quality guidelines. Emission estimates for CO, NOx, SOx, VOC, CO2, benzene and PM2.5 were also made. Sources examined included domestic home heating, motor vehicles including brake and tyre wear, industrial emissions and outdoor burning. Because of the undulating topography of Nelson, the area was broken down into eight separate airsheds. Results for airshed five (Toi Toi, Broads, Kirks, Bronte, Grampians and part of Britannia Heights) were of particular interest as air quality monitoring indicated PM10 concentrations were of greatest concern in this area.

Figures 2.13 and 2.14 show the majority of the PM10 and PM2.5 emissions across Nelson and within airshed five occur as a result of solid fuel burning for domestic home heating. Outdoor burning and motor vehicles both make only a small contribution (less than 5%). The industrial contribution across the whole of Nelson is larger than in airshed five, which includes only a few coal fired boilers and some minor industrial PM10 sources.

About 96% of the PM10 emissions from domestic heating in Nelson are in the PM2.5 size fraction. This is slightly higher than estimated for Timaru owing to the greater prevalence of the use of coal for domestic heating in Timaru. Across the whole of Nelson, about 65% of the motor vehicle and industrial PM10 emissions are in the PM2.5 size fraction.

Figure 2.13: Relative contribution to wintertime PM10 and PM2.5 emissions across the whole of Nelson for 2001

Figure 2.14: Relative contribution to wintertime PM10 and PM2.5 emissions in the Nelson airshed five area for 2001

2.8 Otago

An air emissions inventory for the Otago region was carried out for the year 1999 and included an assessment of emissions from motor vehicles, domestic home heating and industry. The four contaminants assessed were PM10, CO, NOx and SOx and estimates made for Dunedin as well as the following areas:

  • Alexandra
  • Arrowtown
  • Balclutha
  • Clyde
  • Cromwell
  • Milton
  • Mosgiel
  • Oamaru
  • Queenstown
  • Wanaka.

The area of Dunedin was broken down into a further 17 suburbs and data provided for each of these areas as well as a total for the whole Dunedin area.

Air quality monitoring has been carried out in most of the towns included in the 1999 inventory and results indicate that PM10 concentrations exceed the guideline value in most of these areas.

Figures 2.15 to 2.17 show the relative contribution of different sources to wintertime PM10 emissions in the different study areas. In this case, the domestic emissions category includes backyard burning and lawn mowing as well as home heating. The latter source is dominant, however, contributing over 99% of the PM10 wintertime emissions in Dunedin for example. Similarly the mobile sources include non-road sources such as marine, rail and aircraft emissions.

While domestic home heating is the dominant contributor to wintertime PM10 emissions in these areas, industrial PM10 emissions are significant in most of the towns. In particular, in Mosgiel the industrial PM10 contribution is estimated to be 47% and in Dunedin 37%.

Figure 2.15: Relative contribution to wintertime PM10 emissions in Alexandra, Arrowtown, Balclutha and Clyde for 1999

Figure 2.16: Relative contribution to wintertime PM10 emissions in Cromwell, Milton, Mosgiel and Oamaru during 1999

Figure 2.17: Relative contribution to wintertime PM10 emissions in Queenstown, Wanaka, Dunedin and across all the Otago study areas during 1999

2.9 Gisborne

An emission inventory was carried out for the Gisborne area based primarily on data for 1995. Sources assessed in the inventory include transport (including motor vehicles, aircraft, rail and shipping), domestic combustion, industry, agriculture and natural emissions. Domestic combustion emissions are presented with light industrial, commercial and recreational activities and classified as area sources. Contaminants assessed included total suspended particles (TSP), although transport data were for PM10 estimates, CO, NOx, SOx, VOC, CH4 and CO2.

The methodology used was similar to the Taranaki and Bay of Plenty inventories in that data were presented as annual emission estimates. The methodology for assessing area emissions for the Gisborne region relies on a population-adjusted extrapolation from the Auckland area emissions assessment and thus results should be treated with extreme caution. Figure 2.18 shows the estimated relative contribution of different sources to annual TSP emissions in Gisborne (Wright, 1996).

Figure 2.18: Relative contribution of sources to annual TSP emissions in Gisborne

2.10 Northland

An emission inventory for Northland was carried out based on data for the years 1996 to 2000. Sources included in the inventory were major industrial discharges, domestic heating, waste burning and lawn mowing, motor vehicles and agricultural sources. Contaminants considered in the inventory included PM10, CO, NOx, SOx, VOC, CO2, CH4 and N2O. The latter three contaminants were considered in the context of greenhouse gas emissions.

The methodology included Northland specific statistics as well as extrapolation of data from other areas (e.g. Wellington). Data were presented as contributions to annual average emissions as well as daily emission estimates for the winter period. Industrial emissions assessments were limited to the top 10 industrial dischargers within the Northland region.

The main source of PM10 for a day during the winter was domestic home heating contributing around 50% of the PM10 emissions in the Northland area (Figure 2.19). The industrial contribution was also significant with around 30% of the PM10 from this source.

Figure 2.19: Relative contribution of sources to winter daytime PM10 emissions in Northland

2.11 Total emissions inventory for New Zealand

An assessment of the amount of PM10 from different sources across the whole of New Zealand was carried out by NIWA in 1998 (NIWA, 1998). Sources included in the national emission inventory were broken down into the following categories: area based emissions (predominantly domestic home heating, small scale boilers, lawn mowing, off-road vehicles, open burning), transport, industry and natural emissions. The methodology was less complex than the majority of the regional emissions assessments, with estimates based on broader assumptions. For example, emissions from domestic home heating were assessed based on the results from existing inventories (Auckland and Christchurch for the North and South Islands respectively) and scaled based on population for each area.

The transport emissions assessment in the Total Emission Inventory for New Zealand estimates annual PM10 motor vehicle emissions of 197, 694, 317, 71, 146, 225 and 368 t/year for North Shore City, Auckland City, Manukau City, Wellington and Christchurch respectively. Collectively, estimates for the Auckland area (excluding Rodney District and Franklin) total 1425 t/year or around 3.9 t/day, compared to around two tonnes per day in the 1996 Auckland Regional Emission Inventory (includes parts of Franklin and Rodney). Results from the national inventory assessment for Wellington (around 0.6 t/day) were relatively low compared to the regional estimates for 1997 of 1.2 tonnes. For Christchurch estimates were a bit closer with around 1 t/day for the 1996 national assessment compared to around 0.8 t/day for the 1996 motor vehicles assessment.

The comparability of the total PM10 emission estimates in the national emission inventory assessments to the regional assessments varies with area. In Wellington estimates of around 2500 tonnes per year for the national emission inventory compare to around 1500 tonnes in the Wellington region emission inventory.

In Hamilton annual estimates of around 590 tonnes of PM10 from the regional assessment compare to around 578 in the national emissions inventory. In Taupo, regional assessments indicate around 400 tonnes of PM10 are likely to compare to an estimated 249 tonnes in the national inventory assessment. In Auckland, the regional assessment for 1993 indicates annual emissions for TSP of less than 6000 tonnes per year. This is similar to the national inventory assessment when the areas of Franklin and Rodney are excluded from the assessment. However, if these areas are included, the national assessment indicates around 9000 tonnes of PM10 per year. The regional data includes parts of these areas.

For Christchurch, the national emissions inventory estimate of 3086 tonnes of PM10 per year is greater than around 2000 estimated based on the Christchurch emission inventory 1996 back-cast. A better comparison is observed in Nelson with regional estimates of around 300 tonnes per year compared to 455 in the national emissions inventory.