The simplified on-line COPERT4 methodology for calculating emissions from traffic

Introduction

This article shows how to use the simplified version of the COPERT 4 methodology available on the Enviroware web site. The methodology is based on the contents of the EMEP/CORINAIR Emission Inventory Guidebook 2007, available on the internet site of the European Environment Agency, more precisely on chapter 7, concerning Road transport. Chapter 7 provides the methodology, emission factors and relevant activity data to calculate:

  • the emissions produced by the exhaust systems of road vehicles (SNAP codes 0701 to 0705),
  • the non-exhaust emissions such as fuel evaporation from vehicles (SNAP code 0706) and
  • the component attrition, which means tyre and brake wear and road abrasion (SNAP codes 0707 and 0708).

The simplified methodology allows to calculate the only exhaust emissions. For many European countries, it gives the bulk emission factors in terms of grams of pollutants emitted per kg of fuel consumed. The emission factors at national level have been obtained applying the detailed COPERT 4 methodology using the activity data derived from TREMOVE. Therefore the detailed COPERT4 methodology has been a-priori applied to obtain the simplified emission factors.

The vehicles categories considered by the simplified COPERT4 methodology are Gasoline Passenger Cars (gPC), Diesel Passenger Cars (dPC), Gasoline Light Duty Vehicles (gLDV), Diesel Light Duty Vehicles (dLDV), Diesel Heavy Duty Vehicles (dHDV), Buses, Mopeds and Motorcycles. The simplified methodology does not deal with LPGs, 2-stroke and gasoline heavy-duty vehicles because of their small contribution to a national inventory.

The simplified methodology allows to calculate the exhaust emissions of carbon monoxide (CO), nitrogen oxides (NOX), non-methane volatile organic compounds (NMVOC), methane (CH4), particulate matter (PM), and carbon dioxide (CO2). All PM emissions refer to PM2.5, as the coarse fraction (PM2.5-10) is negligible in vehicle exhaust.

The application of the simplified COPERT 4 methodology must be done keeping in mind that the emission factors

  • correspond to a fleet composition estimated for year 2005, therefore their accuracy deteriorates as time distance increases from such year because new technologies appear and the contribution of older technologies decreases;
  • correspond to national-wide applications including mixed conditions driving (from urban congestion to free flow highway).

The methodology can be useful for example in simplified emission inventories, where rough estimate of the transport contribution is required. It is observed that the methodology is not suitable to be applied over small areas (e.g. a single town), or for a small time period (e.g. few days), because in such cases it would be even more approximated.

Example of input data

The emission factors are given as function of fuel used by the transport sector, therefore the first step is to obtain information about the total amount of fuel used. Considering for example Italy, for the whole country and for year 2008, such information can be obtained from the internet site of the Italian Oil Union (Unione Petrolifera). In 2008 Italy has consumed, for the road transport sector, 11044 Gg of gasoline, and 25934 Gg of diesel.

Since we want to estimate the emissions in Italy, an assumption that we have to do is that all this fuel has been consumed in Italy, even if a fraction of it has been consumed abroad. Similarly there will be a fraction of fuel sold abroad and consumed in Italy.

Other assumptions are needed to split the fuel consumption among the vehicle classes listed above (gPC, dPC, gLDV, dLDV, dHDV, buses, mopeds and motorcycles). A precise calculation of the consumption split is beyond the scope of this article, however it is worth to say that there are methodologies and software which allow a reliable estimate of the consumption of each vehicle class. The EMITRA software, for example, uses the actual fuel consumption, the number of vehicles and the vehicles fleet as known input data, then calculates the total consumption starting from assumed values of the average speed on different road types and of the average trip length for each vehicle type. If the calculated consumption is equal to the actual consumption, or at least comparable within a degree of acceptability, the fuel split is automatically obtained. Otherwise the procedure is repeated using different values for the average speeds and the average trip lengths until the convergence is reached.

For this example we will simply assume that the fuel is consumed as summarised in the following pie charts, which is, for gasoline, gPC: 93%, gLDV: 4 %, mopeds: 1%, motorcycles: 2%, and for diesel, dPC: 41%, dLDV: 11%, dHDV: 43% and buses: 5%.

Therefore the Gg of fuel consumed by the different vehicle classes is gPC 10270.9; gLDV 441.8; mopeds 110.4; motorcycles 220.9; dPC 10632.9; dLDV 2852.7; dHDV 11151.6 and buses 1296.7.

These numbers are then used as input data for the on line procedure. We need to select Italy among the available countries, then we must insert the fuel consumption for each vehicle class, paying attention to the units because the above numbers are in Gg (i.e. kilotonnes), while the system needs them in Mg (i.e. tonnes). An example of the input mask is shown in figure.

Results

The results of the on line simplified COPERT 4 methodology are given both in numerical terms and graphically. A table (see the figure) gives the total emissions calculated for each pollutant and for each vehicle class. The emission units are automatically decided by the software starting from their values, they can be kg, Mg and Gg. Moreover, six pie charts, one for each pollutant, show the amount of emissions due to each vehicle class.

Using the input data discussed before, the amount of estimated emission due to road transport over the whole Italy are 1910.9 Gg of carbon monoxide, 703.2 Gg of nitrogen oxides, 206.7 Gg of NMVOC, 15.0 Gg of methane, 26.8 Gg of particulate matter and 116.3 Tg of carbon dioxide. As shown by the pie charts below, which are automatically produced by the on line simplified COPERT 4 methodology, the greatest amount of carbon monoxide is emitted by gasoline passenger cars (gPC), which is responsible for the emission of more than 81% of the total. More than 52% of nitrogen dioxides is emitted by diesel heavy duty vehicles, while passenger cars, both gasoline and diesel, are responsible for the emission of about 17% each one. Methane and NMVOC are mostly emitted by gasoline passenger cars (about 60% of the total). Important emissions of particulate matter, which is all PM2.5, are due to heavy duty vehicles (more than 37% of the total) and to diesel passenger cars (more than 34% of the total). Finally, the greatest emissions of carbon dioxide are due to heavy duty vehicles (30.1%), diesel passenger cars (28.7%) and gasoline passenger cars (27.9%).

In a typical emission inventory, now that we have the total emissions of each pollutant, other steps would follow. Among these steps, four important ones are:

  • the spatial disaggregation of the emissions (i.e. how they distribute over the territory);
  • the temporal disaggregation of the emissions (i.e. how they distribute over the months, the days of the week and the hours of the day);
  • the chemical speciation of the NMVOC (i.e. the determination of the chemical species within this pseudo-species which contains all the volatile organic compounds but methane);
  • the NOX speciation into NO and NO2.

Concerning the chemical speciation, the CORINAIR methodology contains the fraction of species (alkanes, cycloalkanes, alkenes, alkines, aldehydes, ketones and aromatics) for each vehicle category and fuel type. Even the NOX speciation, indications are given within the CORINAIR methodology.

The size speciation of particulate matter would be another task in an emission inventory but, as stated above, all the road traffic exhaust emissions of PM refers to PM2.5. Finally, concerning the PM speciation in elemental and organic carbon, the CORINAIR methodology contains ratios for different vehicle technologies.