Appendix B Emission conversion factors

This Appendix provides representative emission factors for the Australian vehicle fleet for average driving conditions. It shows a series of conversion factors from fuel (litres) to emissions (g/l)) across on-road vehicles for a range of vehicle types and age classifications from pre-1976 to the portion of the vehicle fleet manufactured from 2008 to 2014.

These figures have been calculated by BITRE and are based on averaging results of various models (with varying input parameter settings, such as for congestion effects or annual vehicle deterioration rates) across BITRE MVEm (which includes calibrations using NISE1 and NISE2 data, such as reported by FORS and Orbital Australia) and COPERT for Australia (www.emisia.com), and have been compared with summary results reported in NGGIC 2006 and the National Inventory Report 2012 (Department of the Environment, 2014).

Note:

Post 2008– represents current averages across on-road estimates for all new vehicles manufactured after 2006, from 2008 to 2014. It is acknowledged that each year from 2014, new vehicle sales will be added to this topmost age category, typically with slightly better noxious emission performance than these current group averages. Therefore, the actual 'post-2008' levels will tend to gradually decline over time, although these present values (for the newer portion of the fleet) should be sufficiently applicable in the short term, since it is predicted to be several years before any such declines in the averages become noticeable.

For some of the fuel types, no date is reported. This is because there are insufficient background data to accurately derive different emission rates by age of vehicle. Therefore average values are given across that portion of the current fleet (i.e. for all on-road vehicles of that vehicle and fuel type).

Source: Email communication BITRE, November 2014; COPERT Australia (EMISIA 2014); Department of the Environment (2014)

Notes to emission conversion factors

As advised by BITRE (Email communication, November 2014), the above emission factors relate to emissions directly from vehicles and do not include any 'upstream' emissions due to vehicle or fuel provision, such as motor vehicle manufacturing, petrol refining or power generation for electric vehicle use.

The CO₂ values have had standard 'oxidation factors' applied to them, assumed by the Department of the Environment to be approximately 99% for liquid fuels (approximately 1% of fuel carbon is not released as CO₂, but ends up as residual ash). These values otherwise follow the standard convention of assuming complete combustion to CO₂. It is assumed that all the fuel carbon not ending up as residual ash is fully oxidised by the engine and is released as CO₂. However, in actual real world conditions, a portion of the fuel carbon is not directly emitted as CO₂, but as CO, CH₄ and other volatile organics, with most of this portion later oxidising to CO₂ in the atmosphere.

The NMVOC results include allowances for evaporative emissions. For the current passenger car fleet, approximately 30% of NMVOC emissions from vehicles are due to exhaust emissions, with the remainder being evaporative releases, while the vehicles are either driven or parked. Average daily evaporative emissions have been prorated over average distance travelled, at average operating fuel consumption rates.

PM₁₀ values (for particulate matter emissions smaller than 10 microns in diameter) relate to exhaust emissions (i.e. do not include wear particulates from abrasion of tyres, brakes and the road surface; or secondary particulates, such as sulphates and nitrates, formed later in the atmosphere from other vehicle emissions). For the current passenger car fleet, exhaust particulate emissions comprise approximately 20% of total PM₁₀ from vehicle use (from exhaust, wear including the fine component of re-suspended road dust and secondary sulphate/nitrate). Of the PM₁₀ exhaust releases, typically around 30-40% is in the form of black carbon, one of the most significant greenhouse emission species.

Estimation of emissions from E10 usage can be roughly approximated by using the petrol values for equivalently sized vehicles. This is because, for low percentage ethanol blends, output of most emission species should not typically differ extensively.

Values for natural gas (NG) buses are provided in terms of 'grams emitted per litre of diesel equivalent'. This represents the unit emissions from the consumption of an amount of natural gas with the same energy content as a litre of ADO.

Due to limited in-service testing data, especially for some vehicle/fuel types, many emission factors are quite approximate. Some factors (such as for CO₂ and SO_x) are directly related to average fuel properties and will typically not alter under different driving/vehicle conditions. For others such as CO and VOC emissions, these are more dependent on the particular engine operating characteristics, and will typically alter depending on driving or ambient conditions. For example, with travel under purely congested driving conditions, several such emission factors will generally be higher than these median level values; and conversely, for purely highway driving, such emission factors will tend to be lower than these provided averages.