Menu
Home
Log in / Register
 
Home arrow Business & Finance arrow Green Transportation Logistics
< Prev   CONTENTS   Next >

2.2 Calculating Emissions

There are generally two main methods that can be used to produce fuel consumption and emission estimates for transportation activities. The first method is called the 'top-down' method, or 'fuel-based' method, and uses fuel sales to estimate emissions. This would be the most reliable method of estimating total fuel consumption and emissions if the figures of fuels sales that are reported are absolutely reliable. Fuel sales figures are mainly collected from energy databases published by the Energy Information Administration (EIA), the International Energy Agency (IEA) and the UNFCCC. However, due to difficulties mainly because of unreliable or inaccurate fuel sale statistics, an alternative method has emerged. This is the so-called 'bottom up' method, or 'activity-based' method. This is an approach based on 'fleet activity,' that is, information on movements and vehicle characteristics (vehicle type and size, engine type and age, fuel type, etc.), as well as the corresponding fuel consumption figures and emission factors.

Below we describe each method and also comment on additional methods to calculate emissions.

2.2.1 The Top-Down or Fuel-Based Approach

According to this method, to estimate emissions from transportation one should multiply the energy or fuel used by an appropriate 'emissions factor.' The following equation may be used:

where

Energy or Fuel Consumption is the energy or fuel source consumption related to the operational profile of the engine used and is typically expressed as hp-h, kW-h, or MW-h (energy), or gallons, kg or tonnes (fuel consumption).

Emissions Factor is the ratio of emissions produced per unit energy or unit fuel consumed. In general this factor is a function of type of emissions, type of fuel and type of engine and is typically expressed in g/hp-h, g/kW-h, or g/MW-h (energy); or, lb/gal, g/kg or tonne/tonne (fuel consumption).

If a number of different fuels are used by various engines or energy sources on the vehicle and fuel consumption is used as an input, Eq. (2.1) translates into

Emission estimates based on real fuel consumption data are the most accurate. In this case, one may use empirically-based emissions factors to estimate the emissions. As said earlier, these factors depend on the fuel type (in the case of CO2), the sulphur content (for SO2) or the engine itself (for NOx). There are a wide variety of sources for emission factors that can be used to estimate emissions from transportation activities. Much work has been done related to GHG emissions basically due to mandatory reporting as per Kyoto Protocol. For non-GHGs, the literature is very fragmented as many national authorities (such as the US Environmental Protection Agency and the UK Department for Environment, Food and Rural Affairs) provide guidance documents on how to estimate non-GHG emissions. A reliable source of emission factors is the 'Air pollutant emission inventory guidebook' published by the European Environment Agency. See Table 2.1 for some typical factors.

Emissions are also indirectly produced if the vehicle is driven by electrical motors, even though obviously there are no emissions generated by the vehicle itself. This is due to the fact that the source that generates the electrical energy that

Table 2.1 Emission factors (in g/kg fuel)

Sector/fuel type

CO2

NOX

PM10

SO2

Aviation (jet kerosene)

2,600

8.3

0

0.8

Railways (gas oil/diesel)

3,140

52.4

1.44

Shipping (bunker fuel oil)

3,170

79.3

6.2

20

Shipping (marine diesel/marine gas oil)

3,140

78.5

1.5

20

Road (passenger car—gasoline)

3,180

8.73

0.03

0.08

Road (heavy duty vehicle—diesel)

3,140

33.37

0.94

0.016

Road (bus—compressed natural gas)

2,750

13

0.02

Compiled from EMEP/EEA (2013)

Table 2.2 Electricity emissions factors (g/KWh)

is used by the vehicle will generally produce emissions. Then emissions are calculated as follows:

where again EF are the total emissions produced, and

FE is the emissions factor (in g/kWh),

f E j is electrical energy used by each motor j (in kW-h) and

NE is the number of different electricity sources used.

Note that the electrical energy is the energy input to the equipment and is usually taken from utility bills or electricity meters. To estimate the emissions produced when using electricity one must know the mix that is used to produce this energy. Table 2.2 presents the emission factors to estimate emissions for producing electricity from various sources based on the so-called RAINS model.

Note that in many studies emissions from producing electricity by using hydro,

wind, nuclear or solar energy are supposed to be zero. However, in reality, it would be more appropriate to use LCA (Life Cycle Assessment) emission factors, which take into consideration the overall life cycle of the energy carrier and includes not only the emissions of the final combustion, but also all emissions of the whole supply chain (exploitation, transportation, processing, etc.). LCA Emission factors for CO2 are given in the Covenant of Mayors' Sustainable Energy Action Plan (SEAP), see European Commission (2010). Thus, emission factors are heavily based on the energy mix used to produce electricity. As a random example, the CO2 emission factor for the energy mix in Greece is 1.149 g/kWh (due to the widespread use of lignite) whereas the EU-27 average is 460 g/kWh. LCA emission factors are 1.167 and 578 g/kWh respectively. More on the LCA approach for emissions can be found in Chap. 11 of this book.

 
Found a mistake? Please highlight the word and press Shift + Enter  
< Prev   CONTENTS   Next >
 
Subjects
Accounting
Business & Finance
Communication
Computer Science
Economics
Education
Engineering
Environment
Geography
Health
History
Language & Literature
Law
Management
Marketing
Philosophy
Political science
Psychology
Religion
Sociology
Travel