Chapter 4 Inventory Analysis of Emissions and Extractions
4.3 Inventory Databases for Process-Based Approach
4.3.2 Ecoinvent
4.3.2.1 The Project and Its Products
Ecoinvent is a project aiming to combine and enhance different existing inventory databases to obtain a unified and generic inventory data set of extremely high qual-ity. Initially developed for Switzerland and western European countries, it is increas-ingly adapted to global data sets.
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4.3.2.2 Description of the Ecoinvent 2.2 Database
Inventory data (v.2.2) are compiled for a large number of products and services, representing production and supply mostly from the year 2000. In addition to the quantitative information about inflows and outflows, supplementary descriptive information (metainformation) is provided on the technological, temporal, and geo-graphic validity.
The database is organized according to the following main categories:
• Energy sources
• Construction materials and processes
• Chemicals
• Detergents
• Paper
• Waste treatment services
• Agricultural products and processes
• Transportation
The ecoinvent database consists of more than 4000 processes linked by material and energy flows covering more than 400 substances and resources. Ecoinvent CO2
emissions and nonrenewable primary energy use are provided for approximately 50 processes in Appendix III.
4.3.2.3 Principal Characteristics of the Database
The ecoinvent database was initially developed for western Europe, with country- or region-specific values for certain processes. Whenever possible, data are provided on a unit process level, and only aggregated when unit process data are not available or confidential. The most common types of processes and emissions are described in the following paragraphs.
The inflows and outflows for the production processes are generally provided separately from those of the production infrastructure, allowing the user to choose whether to include certain infrastructures.
Electricity is modeled based on average electricity mixes, which are available for multiple European countries and other countries such as the United States, Japan, and China. Electricity mixes specific to other countries may be available and used to calculate new mixes. The database differentiates the production mix from the supply mix, where the latter is used for most processes requiring an energy demand. The production mix is only used for processes within the electric sector.
Transportation often occurs between the processes of a system. Due to the dif-ficulty in determining the means and distances of transport for all individual inter-mediary products, standard distances are used by default.
Waste treatment is modeled like all other technical processes as another part of the system. If the specific waste treatment processes are not known, generic treat-ment processes are applied.
Certain elementary flows are always neglected; specifically, the sound emissions (noise) and H2, N2, and O2 air emissions.
68 Environmental Life Cycle Assessment Regarding the material and energy flows, the nonrenewable primary energy is calculated based on the lower heating value (LHV) given in Table 4.7. The higher heating value (HHV) of a fuel is the amount of energy contained in the fuel; the LHV is the effective heat released during combustion, determined by subtracting the heat of vaporization of the water vapor from the HHV. For uranium, it is the reduction of its potential heating value due to its use in a power plant that is taken into account.
For air emissions, certain common pollutants are treated as follows:
• Benzene emissions are reported under the “benzene” label rather than as “aro-matic hydrocarbons” or nonmethane volatile organic compounds (NMVOCs).
When NMVOCs and benzene emissions are both measured and reported, the NMVOC emissions are input after subtracting benzene emissions.
• Particulate emissions to the air are classified based on three categories of particulate diameters. PM2.5 refers to particles less than 2.5 µm in aero-dynamic diameter, PM10−PM2.5 are particles between 2.5 and 10 µm, and TPM−PM10 are particles greater than 10 µm (total particulate matter [TPM]
minus particles smaller than 10 µm).
• For CO2, CO, and CH4, a distinction is made between fossilized sources and biogenic sources. In the biogenic case, the carbon fixed during bio-mass growth is considered a CO2 extraction from the atmosphere, which is rereleased during combustion or degradation. Maintaining this distinction allows the correct accounting of waste treatment processes responsible for TABLE 4.7
Lower Heating Value (LHV), Higher Heating Value (HHV), and Densities of Fuel Sources in the Ecoinvent Database
LHV (MJ)
HHV (MJ)
Density (kg/La)
Gasoline kg 42.8 45.8 0.75
Diesel kg 42.8 45.5 0.84
Kerosene kg 43.3 46.0 0.80
Light oil kg 42.7 45.4 0.84
Heavy oil used in boilers (Switzerland) kg 40.6 43.0 0.95
Heavy fuel used in boilers/electric plants (Europe) kg 40.0 42.3 1.00
Natural gas (Europe) Nm3 36.8 40.4 0.80
Nuclear kg 560,000 – –
Hardwood, dry kg 18.3 – 239
Softwood, dry kg 19.1 – 169
Mixed wood kg 18.9 – 189
Source: Dones, R., et al., 2004. Life Cycle Inventories of Energy Systems: Results for Current Systems in Switzerland and other UCTE Countries, Data v1.1, ecoinvent report No. 5, Dübendorf, Switzerland.
a Except for the density of wood, which is expressed in kilograms per cubic meter.
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a significant fraction of CO2 emissions. If biogenic CO2 fixed during bio-mass growth is accounted for, special care must be taken to ensure that the corresponding release of CO2 is also taken into account during usage (e.g., food, combustion processes) or product end of life (e.g., incineration, land-fill). A pragmatic solution to ensure reliability is to only account for fossil (nonbiogenic) CO2 releases, and to assume that biogenically fixed CO2 is eventually released over the whole life cycle. Note that in the case where methane is released instead of CO2, this should then be taken into account due to the differences in the global warming potential of each substance.
• Sulfur and nitrogen oxides, SOx and NOx, are each grouped under the SO2 and NO2 labels, respectively.
• Air emissions of trace elements are provided by metal type and speciation, when available.
• For polycyclic aromatic hydrocarbons (PAHs), benzo[a]pyrene emissions are provided separately.
• The dioxin and furan emissions are expressed as equivalent 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD) emissions.
For water-based transmissions, four aggregated parameters characterizing organic carbon content are reported: the biological oxygen demand (BOD5), the chemical oxygen demand (COD), the dissolved organic carbon (DOC), and the total organic carbon (TOC). If necessary, these parameters are calculated from individual pollut-ant qupollut-antities, which are also available in the inventory.
Particular attention has been given to land use and transformation. Land use contributes to increased competition between users, biodiversity loss, changes on climatic equilibrium, and the degradation of cultural assets. A distinction is made between land use (surface and duration required for the production of a certain quan-tity of goods and services) and land transformation (which relates the state of the land throughout an economic activity to its earlier and later state). No regional differ-entiation can be made, since data is collected at the level of national averages. As far as possible, unit processes are characterized by a geographic code, which specifies the country or continent where the use and transformation of soil take place.
In the ecoinvent database, careful attention has been given to the quality of data and their analysis. Section 6.5 describes the approach used to characterize uncer-tainty, and this can be applied to the assessment of new data.
4.3.2.4 New Features of Ecoinvent 3.1
The updated ecoinvent 3.1 improves on v.2.2 by consistently modeling water flows throughout the whole database, enabling the practitioner to determine water use and consumption to calculate the water footprint of products (Weidema et al. 2011). It also provides updated data sets for electricity production (more than 20 additional countries worldwide), the wood sector, recycling activities, chemical production, and fruit and vegetables. In addition to the more traditional attributional modeling, eco-invent 3.1 can potentially support cut-off and consequential system modeling.
In the cut-off model, “the primary producer does not receive any credit for the provision of any recyclable materials. As a consequence, recyclable materials are
70 Environmental Life Cycle Assessment available burden-free to recycling processes, and secondary recycled materials bear only the impacts of the recycling processes” (www.ecoinvent.org). Alternatively, allocation at the point of substitution allocates “the valuable by-products of treat-ment systems together with the activity that produced the material for treattreat-ment”
(www.ecoinvent.org). While this is beneficial in avoiding difficult allocations, its present implementation may be problematic. For example, in the case of a plastic that was primarily used for agriculture and then recycled, the user of the recycled plastic would be allocated some nitrate burden from agriculture production, even though that had little to do with the primary plastic production itself. Due to these poten-tial problems with allocation at the point of substitution, we currently recommend using the cut-off model. Before being a recommendable approach, we believe the allocation at the point of substitution should be preceded by a partial process sepa-ration. For example, in the recycled plastic example, only plastic-related processes (upstream plastic manufacturing) should be partially allocated to the recycled mate-rial, leaving emissions directly related to the agriculture practice entirely allocated to agriculture.
4.3.2.5 Tips for Using Ecoinvent Database
Some tips follow for selecting the appropriate energy and transportation data in the ecoinvent database.
For the electricity mix, it is important to choose the geographical region appropri-ate to the case being studied, which is either the consumption mix of the country of production or the electricity type that effectively responds to a marginal increase in electricity demand. For example, an increase in Swiss electricity consumption may have little effect on Swiss production, but may instead be satisfied by an increase in electricity production elsewhere in Europe, such as a thermal gas power plant. We also determine the right voltage level among the three existing types (low, medium, and high voltage). The medium voltage corresponds to industrial use, and low volt-age to domestic use, commerce, and agriculture.
Data in the energy sector can be provided in three forms: (a) by mass or volume of combustible, (b) by megajoules of final energy, or (c) by megajoules of useful energy.
(a) The emissions and extractions listed by quantity of combustible (liters of oil, kilograms of petroleum, cubic meters of natural gas, or kilograms of wood) account for associated transport and distribution to users (industrial, commercial, agricul-tural, and domestic), but do not account for combustion. Emissions associated with the combustion of energy carriers need to be added separately, accounting for a separate process corresponding to the combustion type. The natural gas inventory data are provided for both low- and high-pressure networks, where “low pressure”
generally corresponds to domestic, commercial, or agricultural consumption, and
“high pressure” refers to industrial consumption.
(b) The processes expressed in megajoules of final energy—the energy bought by the client—account for the combustion and are named in a similar manner to com-bustibles, with the energy carrier’s name followed by the term burned.
(c) The inventory data reported by megajoules of useful energy describe the sup-ply of useful heat, such as the heat delivered inside a building. These processes also
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account for the combustion stage, and have names starting with heat followed by the energy carrier’s name.
Regarding truck transportation, ecoinvent provides average data assuming an empty truck on the return trip (process names beginning with transport), but data are also available for fully loaded and empty trucks (process names beginning with operation). In this case, data must be added on vehicle production and disposal, as well as on traffic infrastructure.
Given the array of processes and potential for error in using the ecoinvent data-base, we advise using specialized LCA software (Section 6.7) to analyze and aggre-gate ecoinvent data. It is still recommended, however, to examine the raw ecoinvent data and estimate a simple CO2 or energy balance by hand to check the results of software and identify potential problems.