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Annex 2: Methodology and data collection for estimating emissions from fossil fuel combustion

New Zealand emission factors are based on GCV (gross calorific value). Energy use in New Zealand is conventionally reported in gross terms, with some minor exceptions. The convention adopted by New Zealand to convert GCV to NCV (net calorific value) follows the Organisation for Economic Co-operation and Development (OECD) and International Energy Agency (IEA) assumptions (IEA, 2005):

  • NCV = 0.95 x GCV for coal and liquid fuels

  • NCV = 0.90 x GCV for gas.

A2.1 Emissions from liquid fuels

Activity data

Activity data

Statistics New Zealand conducts the “Delivery of Petroleum Fuels by Industry Survey”. This survey is run as a quarterly census. The purpose of the census is to provide data on the amount of fuel delivered by all oil companies to end-users and other distribution outlets. Each oil company in New Zealand supplies Statistics New Zealand with the volume of petroleum fuels delivered to resellers and industry groups. It is assumed there is a five per cent uncertainty associated with the sectoral energy allocation although the annual totals are likely to be more certain (MED, 2006a).

Because the “Delivery of Petroleum Fuels by Industry Survey” is run as a census there is no sampling error. The main sources of non-sample error are:

  • Respondent error: Statistics New Zealand makes every effort to confirm figures supplied by respondents, and given assurances of accuracy. Statistics New Zealand is bound to accept them. If a discrepancy is discovered at a later date, revised figures are supplied at the earliest possible opportunity.

  • Processing error: there is always the possibility of error, however, Statistics New Zealand has thorough checking procedures to ensure that the risk of processing errors is minimised.

Emission factors

Carbon dioxide emission factors are described in table A2.1. The CO2 emission factors for oil products are from the New Zealand Refining Company (NZRC) data, import data from industry and from Baines (19933). The same values are used for each year of the inventory. There is a direct relationship between each fuel’s carbon content and the corresponding CO2 emissions during combustion. However, the carbon composition of oil products is not closely monitored and there will be variation over time, depending on the crude oil used in production. The New Zealand Refining Company estimates the uncertainty in emission factors to be within five per cent (MED, 2006a).

A review of New Zealand’s energy emission factors (Hale and Twomey Ltd, 2003) identified a number of non-CO2 emission factors (tables A2.2 and A2.3) where the supporting information (Bone et al, 1993; Waring et al, 1991) was assessed to be insufficient to retain the country-specific emission factors used in previous inventories. Where a country-specific value is not available, New Zealand uses either the IPCC value that best reflects New Zealand conditions or the mid-point value from the IPCC range. All emission factors from the IPCC guidelines are converted from NCV to GCV.

Following the initial review under the Kyoto Protocol in February 2007, New Zealand changed the CO2 emission factor for gaseous fuels in “stationary combustion” and the CH4 emission factor for gasoline and diesel oil in “road transportation”. Explanations of these changes can be found in sections 3.2.1.5 and 3.2.3.5.

Table A2.1 CO2 emission factors used in the energy sector category

View CO2 emission factors used in the energy sector category (large table)

Table A2.2 CH4 emission factors used in the energy sector category

View CH4 emission factors used in the energy sector category (large table)

Table A2.3 N2O emission factors used in the energy sector category

View N2O emission factors used in the energy sector category (large table)

A2.2 Emissions from solid fuels

Activity data

The “New Zealand Coal Sales Survey” conducted by Statistics New Zealand is an ongoing quarterly survey which began on 1 March 1981. The purpose of this survey is to measure the amount of coal which is sold and available to users. The target population is all coal mines and major resellers of coal in New Zealand. Completion of the survey has been approved by the Minister of Statistics. Returning the completed and signed questionnaire is a requirement under the Statistics Act 1975.

The survey is a full coverage of the sector and therefore there are no sampling errors. Non-sampling errors in the survey data may result from errors in the sample frame (ie, units with the wrong New Zealand Standard Industrial Classification), respondent error (ie, wrong values supplied), mistakes made during processing survey results or non-response imputation. Statistics New Zealand adopts procedures to detect and minimise these potential errors.

The three ranks of coal measured are bituminous, sub-bituminous and lignite coal. From 1988 onwards the coal sales questionnaire separated coal sales into seven end-use sectors, however these do not match the IPCC sectors. The sectoral shares of coal use that can be used for the UNFCCC inventory are based on Coal Research Limited’s (CRL) survey of sectoral coal use for 1990 and 1995. Data is interpolated between 1990 and 1995 and extrapolated for all years beyond 1995. The exceptions are for the coal used for “iron and steel”, “public electricity and heat production” and the “residential household” sector where the Ministry of Economic Development use data from the “New Zealand Coal Sales Survey”. Sectoral shares are calculated by:

  • summing the four calendar year quarters of coal sales data from the “New Zealand Coal Sales Survey”

  • subtracting coal exports and coal used by the “residential” sector (from the “New Zealand Coal Sales Survey”) and coal used for “iron and steel” and “public electricity and heat production” (both known accurately) dividing Coal Research Limited’s annual coal tonnage for each sector by the total (excluding exports, steel, electricity and residential coal use) to give sectoral shares of coal use for 1990 and 1995

  • interpolating sectoral shares between 1990 and 1995 and extrapolating for beyond 1995

  • applying the sectoral share estimates to the “New Zealand Coal Sales Survey” total coal sold (excluding exports, electricity, steel and residential coal use).

The process of dividing coal use between different sectors will introduce uncertainty larger than the uncertainty in total coal sales. Uncertainty is also introduced from the assumption that coal used by sector is an average of the different ranks. These assumptions are thought to introduce an uncertainty of ± 5 per cent (MED, 2006a).

The sectoral partitioning used for coal was examined in 2003 by officials from the Ministry for the Environment. There was concern in extrapolating sectoral allocations from 1995 to 2002 given some probable changes in sectoral coal usage. However, coal industry experts (Hennessy, pers. Comm.) did not consider a survey could be justified because of the difficulty and expense in collating and verifying data from a number of sectors. Besides, the major categories of coal exports, coal used by the residential sector and coal used for steel and electricity are all known accurately and are not affected by the sectoral partitioning.

Emission factors

The value for sub-bituminous coal (91.2 kt CO2/PJ) is used to calculate New Zealand’s emissions from coal burning (table A2.1). Using only the sub-bituminous value for all ranks of coal is a reasonable assumption for New Zealand as the bulk of the high-quality bituminous coal is exported and all coal used in public electricity generation is of sub-bituminous rank (MED, 2006a). The range in emission factors across all grades of coal is 5.5 per cent. Therefore the estimated uncertainty in coal emission factors is taken as ± 3 per cent (MED, 2006a). An uncertainty of ± 2 per cent is used for the sub-bituminous coal used in public electricity generation. All New Zealand values are within 2 per cent of the IPCC defaults (1996). The non-CO2 emission factors are shown in tables A2.2 and A2.3.

A2.3 Emissions from gaseous fuels

Activity data

Vector Limited has contracts with large users that allow metering errors of ± 2 per cent. Whenever the error between the meter-reading and actual gas supplied exceeds 2 per cent, adjustments are made to the reported quantities of gas supplied. The uncertainty is therefore assumed to have an upper limit of ± 2 per cent (MED, 2006a).

Emission factors

The emission factors for natural gas used in distribution and sold to large users are shown in table A2.1. The values are calculated by averaging daily gas composition data supplied by industry. The composition, hence the emissions factor varies slightly between daily measurements. Taking annual bounds, it is estimated that the uncertainty in the natural gas emission factors is less than 1.7 per cent (MED, 2006a).

As discussed in section 3.2.1.5, New Zealand now uses the information reported in the New Zealand Energy Data File (MED, 2006b) to support the calculation of the weighted average annual CO2 emission factor for natural gas. This average emission factor is applied to a number of categories in the energy sector, such as the “manufacturing industries and construction category”.

Table A2.4 Variation in CO2 emission factors for natural gas

Year Maui
(kt CO2 / PJ)
Treated
(kt CO2 / PJ)
Average
(kt CO2 / PJ)

1990

53.2

52.4

53.1

1991

52.9

52.8

52.9

1992

52.9

52.7

52.8

1993

52.6

52.5

52.6

1994

52.4

52.2

52.4

1995

52.1

52.9

52.2

1996

52.2

52.9

52.3

1997

52.3

52.4

52.1

1998

52.1

52.2

52.1

1999

51.8

52.4

51.9

2000

52.1

52.1

52.1

2001

51.9

52.6

52.0

2002

52.3

52.5

52.3

2003

52.0

52.6

52.1

2004

51.9

53.7

52.2

2005

52.0

52.6

52.1

A2.4 Energy balance for year ended December 2005

Table A2.5 New Zealand energy balance for year ended December 2005 (MED, 2006b)

View New Zealand's energy balance for year ended December 2005 (MED, 2006b) [PDF, 66 KB]

3  The LPG CO2 emissions factor was confirmed by checks of 2002 gas data.