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Toolkit for Identification and Quantification of Releases of Dioxins, Furans and Other Unintentional POPs PART II Emission Factors |
Source Group 5 Transport
POPs emissions from transport (road and off-road vehicles) result from incomplete combustion of fuel in engines. Levels of PCDD/PCDF and other unintentional POPs in exhaust gases from vehicles depend on many factors including the type of engine, its maintenance condition and age, technologies of emission reduction applied (catalysts), type and quality of fuel, driving conditions, ambient conditions etc. The assessment of the impacts of these factors on releases is very important, especially when considering the growth in the number of cars. For the purpose of developing a PCDD/PCDF emission inventory, a simple methodology can be used, where PCDD/PCDF emission rates are considered as a function of the type of engine and type of fuel. The impact of these two parameters on PCDD/PCDF concentrations in exhaust gases are among the most studied. Thus, Toolkit emission factors are given according to the type of combustion engine, the type of fuel, and the emission reduction technology applied (catalysts).
Four source categories are included in this group (see Table II.5.1): 4-stroke engines (gasoline fueled engines with spark ignition), 2-stroke engines (gasoline fueled engines with spark ignition), Diesel engines (Diesel fueled engines with compression ignition), and heavy oil fueled engines (mostly turbines). These types of engines are dominant in the transport sector. In addition, other types of engines are also used such as Wankel rotary engines, gas generators etc. These are nevertheless less frequent and may be included into the existing Toolkit categories.
The major fuels used in road transportation are gasoline and Diesel. In smaller volumes, other types of fuels such as liquefied petroleum gas (LPG), compressed natural gas (CNG), liquid biofuels (ethanol, methanol, biodiesel) and hydrogen are used. Their market is growing but, so far, no dioxin measurements are available. In order to accommodate releases from these fuels, the following hypotheses are proposed:
- For LPG-fuelled cars: take the emission factor for 4-stroke engines with catalyst (5a3);
- For oil/gas or oil/gasoline mixtures: the emission factor for Diesel (5c1) should be applied.
As for air transport, the occurrence of PCDD/PCDF has not been reported from aircrafts. Increases in concentrations or changes in patterns of PCDD/PCDF could not be detected in a biomonitoring program at the Frankfurt International Airport on long-term exposure of kale at different locations, i.e., along the runway or close to the terminals. Consequently, it was assumed that the combustion of kerosene in aircraft motors is not a source of PCDD/PCDF and this category is not addressed in the Toolkit (Fiedler et al. 2000a, Buckley-Golder et al. 1999).
Table II.5.1 Overview of source categories included in group 5 - Transport
5 - Transport Potential release route Source categories Air Water Land Product Residue a 4-Stroke engines b 2-Stroke engines c Diesel engines d Heavy oil fired engines With relevance to the provisions of Article 5, sources in this category can be classified as follows:
Table II.5.2. Relevance to Article 5, Annex C of the Stockholm Convention
No Toolkit source category Part II Part III Relevant source category in Annex C 5a 4-Stroke engines
Motor vehicles, particularly those burning leaded gasoline 5b 2-Stroke engines
Motor vehicles, particularly those burning leaded gasoline 5c Diesel engines
Motor vehicles, particularly those burning leaded gasoline 5d Heavy oil fired engines
Motor vehicles, particularly those burning leaded gasoline An example of elaborating source inventory and release estimate for this source group is included in the example inventory 6.
Most gasoline powered internal combustion engines used today in cars, light trucks, motorcycles and other vehicles are 4-stroke engines. These engines follow the thermodynamic combustion cycle invented by Nicolaus Otto, which consists of 4 strokes, namely the intake stroke, the compression stroke, the ignition and combustion stroke, and the exhaust stroke. These four strokes are completed during two full revolutions of the crankshaft. Like all combustion processes, internal combustion engines produce PCDD/PCDF as an unwanted byproduct. Higher emissions have been associated with the use of chlorinated scavengers in leaded gasoline. However, when unleaded gasoline is used and a catalytic converter is installed for the removal of NOx and unburned hydrocarbons, the emissions of PCDD/PCDF are negligible. The only release vector is to air. Other release vectors are not present.
Emission Factors
PCDD/PCDF emission factors for four source classes are listed in Table II.5.3. Revised or newly added emission factors are highlighted in red. More detailed information on how these emission factors have been derived can be found in Annex 41.
Table II.5.3 PCDD/PCDF emission factors for source category 5a 4-Stroke Engines
| 5a | 4-Stroke Engines | Emission Factors (µg TEQ/t fuel burned) | ||||
|---|---|---|---|---|---|---|
| Classification | Air | Water | Land | Product | Residue | |
| 1 | Leaded fuel* | 2.2 | NA | NA | NA | NA |
| 2 | Unleaded gasoline without catalyst* | 0.1 | NA | NA | NA | NA |
| 3 | Unleaded gasoline with catalyst*(**) | 0.001 | NA | NA | NA | NA |
| 4 | Ethanol with catalyst | 0.0007 | NA | NA | NA | NA |
* If consumption data are given in liters (L), note that 1 L of gasoline has a mass of 0.74 kg; thus a conversion factor of 0.00074 must be used to convert liters into tons.
** Emissions from engines with inadequate or out-of-order catalyst should be calculated using class 2 emission factor.
Guidance for Classification of Sources
Class 1 includes all types of gasoline 4-stroke vehicles which are fueled with leaded (ethylated) gasoline (gasoline with a content of lead of more than 0.15 / 0.013 g/l).
Class 2 includes all types of 4-stroke vehicles which are fueled with gasoline excluding ethylated gasoline or LPG, and are not equipped with catalyst or where the catalyst is not adequate or out of order. Euro class 1 vehicles and lower (or their equivalent in other countries) belong to this class.
Class 3 includes all types of 4-stroke vehicles which are fueled with gasoline excluding ethylated gasoline, or LPG and equipped with proper catalyst. Euro class 2 vehicles and higher (and their equivalent in other countries) belong to this class
Class 4 includes all types of 4-stroke vehicles with catalyst which are powered by ethanol or fuel mix (gasoline-ethanol such as E85), where the share of ethanol is of more than 50%.
Activity rates
Activity rates which characterize the transport sector may be assessed using:
- National statistics on motor fuels consumption, export-import, production (trade, customs etc.);
- National statistics on car fleet structure;
- National, regional, local databases on car registration with indication of their state and ecological characteristics;
- International statistics (Eurostat, IEA).
Activity rates necessary for compiling the PCDD/PCDF emission inventory for the transportation sector (i.e. fuel used (sold) and vehicle fleet characteristics) are generally found in two independent data sources. Therefore, in some cases, it is not easy to estimate fuel consumption according to the type of vehicle. Additional research will be necessary. The example inventory 6 shows some models that may be used in such cases.
Level of Confidence
The confidence in PCDD/PCDF emission factors for this source category depends on the source class. Taking into account the levels of PCDD/PCDF concentrations in emissions and their variation according to the source class, a medium confidence level is assigned to class 2 and class 3 emission factors, a high confidence level to class 1 emission factor, and a low confidence level to class 4 emission factor.
Most small gasoline powered internal combustion engines used today in boats, jet-skis, mopeds, small motorcycles, tuk-tuks, lawnmowers, chain saws, and other vehicles are 2- stroke engines. These engines follow the same thermodynamic combustion cycle as the 4-stroke engines, but are limited to 2 strokes: the combined exhaust and intake stroke, and the compression, ignition and combustion stroke. All these strokes occur during only one full revolution of the crankshaft. Lubrication is usually by oil added with the fuel. Therefore, higher amounts of pollutants may be released and the efficiency may be lower than 4-stroke engines. The only release vector is to the air. All other release vectors are not present.
Emission Factors
PCDD/PCDF emission factors for two source classes are listed in Table II.5.4. Detailed information on how these emission factors have been derived can be found in Annex 42.
Table II.5.4 PCDD/PCDF emission factors for source category 5b 2-Stroke Engines
| 5b | 2-Stroke Engines | Emission Factors (µg TEQ/t fuel burned) | ||||
|---|---|---|---|---|---|---|
| Classification | Air | Water | Land | Product | Residue | |
| 1 | Leaded fuel* | 3.5 | NA | NA | NA | NA |
| 2 | Unleaded fuel* | 2.5 | NA | NA | NA | NA |
* if consumption data are given in liters (L), note that 1 L of gasoline has a mass of 0.74 kg; thus a conversion factor of 0.00074 must be used to convert liters into tons.
Guidance for Classification of Sources
Class 1 includes all mobile machinery (mopeds, small motorcycles, tuk-tuks, boats, jet-skis, lawnmowers, chain saws and other) with 2-stroke engines fueled by leaded fuel (with lead content more than 0.15 / 0.013 g/l).
Class 2 includes all mobile machinery (mopeds, small motorcycles, tuk-tuks, boats, jet-skis, lawnmowers, chain saws, and other) with 2-stroke engines fueled by unleaded fuel (with lead content less than 0.15 / 0.013 g/l).
Activity rates
Activity rates which characterize the transport sector may be assessed using:
- National statistics on motor fuels consumption, export-import, production (trade, customs etc.);
- National statistics on car fleet structure;
- National, regional, local databases on car registration with indication of their state and ecological characteristics;
- International statistics (Eurostat, IEA).
Activity rates necessary for compiling the PCDD/PCDF emission inventory for the transportation sector (i.e. fuel used (sold) and vehicle fleet characteristics) are generally found in two independent data sources. Therefore, in some cases, it is not easy to estimate fuel consumption according to the type of vehicle. Additional research will be necessary. The example inventory 6 shows some models that may be used in such cases.
Level of Confidence
PCDD/PCDF emission measurements from this source category are limited; taking into account the heterogeneity of this source group, a low level of confidence is assigned to these emission factors.
Diesel engines are used in heavy trucks, light trucks, passenger cars, locomotives, heavy construction equipment, boats, Diesel generators, pumps, and farm equipment including tractors and other large equipment. These engines use Diesel (light oil) and a 4-stroke cycle. Compression is used for ignition rather than a spark. Air is taken into the cylinder and compressed. Diesel fuel is added at high pressure and burned, resulting in a more efficient use of fuel and lower emissions. Unfortunately, particle emissions in form of soot are also associated with the operation of Diesel engines, due to incomplete combustion especially during the start-up, warming and load changes. Deposition of this soot can lead to releases via residues. Particulate emissions from Diesel engines are well known to contain high concentrations of polycyclic aromatic hydrocarbons (PAH). However, data on PCDD/PCDF concentrations in Diesel soot are not available. As for other unintentional POPs, no data or almost zero emission for recent diesel engines with after-treatment of emissions have been reported (Laroo et al. 2011).
Emission Factors
PCDD/PCDF emission factors for two source classes are listed in Table II.5.5. Revised or newly added emission factors are highlighted in red. Detailed information on how these emission factors have been derived can be found in Annex 43.
Table II.5.5 PCDD/PCDF emission factors for source category 5c Diesel Engines
| 5c | Diesel Engines | Emission Factors (µg TEQ/t diesel) | ||||
|---|---|---|---|---|---|---|
| Classification | Air | Water | Land | Product | Residue* | |
| 1 | Regular Diesel* | 0.1 | NA | NA | NA | ND |
| 2 | Biodiesel | 0.07 | NA | NA | NA | ND |
* if consumption data are given in liters (L), note that 1 L of Diesel has a mass of 0.83-0.86 (depending on brand of Diesel); thus appropriate conversion factor (in the range 0.00083-0.00086) must be used to convert liters into tons.
Guidance for Classification of Sources
Class 1 includes all mobile machinery (heavy trucks, light trucks, passenger cars, locomotives, heavy construction equipment, boats, Diesel generators, pumps, farm equipment etc.) fueled with regular Diesel.
Class 2 includes Diesel vehicles (heavy duty, passenger cars, etc.) fueled with Diesel including 20% or more biofuel.
Activity rates
Activity rates which characterize the transport sector may be assessed using:
- National statistics on motor fuels consumption, export-import, production (trade, customs etc.);
- National statistics on car fleet structure;
- National, regional, local databases on car registration with indication of their state and ecological characteristics;
- International statistics (Eurostat, IEA).
Activity rates necessary for compiling the PCDD/PCDF emission inventory for the transportation sector (i.e. fuel used (sold) and vehicle fleet characteristics) are generally found in two independent data sources. Therefore, in some cases, it is not easy to estimate fuel consumption according to the type of vehicle. Additional research will be necessary. The example inventory 6 shows some models that may be used in such cases.
Level of Confidence
PCDD/PCDF emission measurements from regular diesel engines are limited, taking into account the large number of vehicles; also, emission may vary widely according to the engine technology, mileage and maintenance conditions. A medium level of confidence is assigned to class 1 emission factor. Furthermore, the use of biodiesel is more recent and emission data are also limited. Thus, a low/medium level of confidence is assigned to class 2 emission factor.
Heavy fuel oil (HFO) fired engines are used for ships, tanks, stationary power generators, and some other large quasi-stationary motors. The availability of emission factors is very limited and presently no distinction can be made with respect to the composition of the fuels, chlorine content, type of catalytic metals present, etc.
Emission Factors
PCDD/PCDF emission factors for one source class are listed in Table II.5.6. Revised or newly added emission factors are highlighted in red. Emission factors for other unintentional POPs (HCB and PCB) were also derived based on Cooper (2005) and are listed in Annex 44. Detailed information on how default emission factors have been derived can also be found in Annex 44.
Table II.5.6 PCDD/PCDF emission factors for source category 5d Heavy Oil Fired Engines
| 5d | Glass Production | Emission Factors (µg TEQ/t fuel burned) | ||||
|---|---|---|---|---|---|---|
| Classification | Air | Water | Land | Product | Residue | |
| 1 | All types | 2 | NA | NA | NA | ND |
Activity rates
Activity rates which characterize the transport sector may be assessed using:
- National statistics on motor fuels consumption, export-import, production (trade, customs etc.);
- National statistics on car fleet structure;
- National, regional, local databases on car registration with indication of their state and ecological characteristics;
- International statistics (Eurostat, IEA).
Activity rates necessary for compiling the PCDD/PCDF emission inventory for the transportation sector (i.e. fuel used (sold) and vehicle fleet characteristics) are generally found in two independent data sources. Therefore, in some cases, it is not easy to estimate fuel consumption according to the type of vehicle. Additional research will be necessary. The example inventory 6 shows some models that may be used in such cases.
Level of Confidence
PCDD/PCDF emission measurements from this source category are limited, taking into account the large number of vehicles, technology, fuel variability, age and maintenance conditions. PCDD/PCDF emission factors are thus provided with medium confidence.
