LIFE CYCLE
ASSESSMENT (LCA):
DESCRIPTION AND
METHODOLOGY
Photo by Warren Gretz, NREL 03783.
The environmental impacts of processes or
activities are growing concerns as the global
implications of these impacts are observed.
Although carbon equivalents are considered
to be a major factor in climate change, other
emissions (air, water, and soil) can have
major environmental and human health
implications locally, regionally, and globally.
Life cycle assessment (LCA) methodology
is a quantitative procedure to evaluate
environmental impacts related to emissions
within a set system boundary, commonly
including climate change as a category. Many
groups are using LCA-derived data and models
to drive business and policy decisions. This
publication reviews the methodology behind
LCA and describes an example analysis for
grain production from maize.
LIFE CYCLE ASSESSMENT BACKGROUND
An LCA can be employed for carbon accounting and used
to evaluate other critical environmental impacts, such
as acidification, ozone depletion, eutrophication, smog,
and human health effects (Table 1). A related publication,
AG-793 Carbon Accounting: Description and Methodology,
reviews the intricacies of global climate change and
carbon accounting. The LCA process is similar to carbon
accounting, except it can be used to evaluate a larger
number of emissions and impact factors using a life
cycle approach. The guiding principles of an LCA follow
the International Organization for Standardization (ISO)
standards ISO 14040 (ISO, 2006a) and ISO 14044 (ISO,
2006b). These two ISO standards provide an overview of
the steps of an LCA: (1) Goal and Scope Definition; (2) Life
Cycle Inventory Analysis; (3) Life Cycle Impact Assessment;
and (4) Interpretation.
LIFE CYCLE ASSESSMENT PROCESS
This section will present an overview of the LCA procedure.
For further guidance, consult ISO 14040 (ISO, 2006a)
and ISO 14044 (ISO, 2006b). While proper preparation is
imperative to conducting an LCA, experience is incredibly
important. The interpretation phase, however, allows for
further modifications throughout the analysis
Goal and Scope Definition
The goal and scope definition provides structure for
the analysis to ensure uniformity. The study’s goals
need to include the rationale for conducting the LCA,
the intended audience, and whether results are to be
publically disclosed. The project scope of an LCA is the
planning stage with areas of determination such as system
boundary, functional unit/allocation, data requirements/
quality, and report format/need for critical review. Other
aspects of the goal and scope definition are outlined in
the corresponding ISO standards (ISO, 2006a; ISO, 2006b).
A well-defined goal and scope definition will assist later
in the analysis when the sheer immensity of calculations
seems staggering.
Setting a proper system boundary is arguably the most critical
aspect of the goal and scope definition and, possibly, the entire
LCA process. Fundamentally, this is a process model with the
system boundary dictating what will and will not be analyzed in
the system. A process model is a conceptual model of a system
broken down into process units (e.g., harvest) and appropriate
flows between units (e.g., fuel, lubricant, and product move to
subsequent operations). It is impractical to analyze all aspects
of a system because of the complexity of minute details, such as
equipment production specifics, and the circuitous nature of the
analysis (e.g., petroleum fuels are utilized to transport petroleum
fuels). This circular pattern of many indirect emissions requires
an allocation procedure to be established at the start of the
analysis.
Depending on system specifics, the boundary can be modified
considerably while staying within the LCA framework. The
boundary will be affected by the goals of the analysis and
whether or not the results will be used for comparative analysis.
It is possible to focus only on direct impacts, such as those
coming from the facility, and ignore indirect impacts, such as
those from upstream and downstream processes. Direct impacts
are compiled from both point sources (e.g., a sewage pipe
running into a stream), some of which have existing monitoring
guidelines, and non-point sources (e.g., runoff across a field into
a stream), which can be difficult to assess. When evaluating
indirect impacts, one method is to quantify inputs and outputs
from the system, then use either information from vendors or
standardized data from an inventory database. Focusing only
on direct emissions, and disregarding the entire life cycle, is
only appropriate in limited circumstances and requires proper
reporting.
Use of a consistent functional unit (e.g., kilograms of product
generated) provides a reference to ensure data uniformity.
The significance of this practice is related to the allocation
procedure, especially when multiple products are produced
from a single system. It is preferable to differentiate by
product production pathway; however, this differentiation is
not always possible, and it requires an allocation procedure.
If the functional unit encompasses the entire system—a
farm for example—an allocation procedure is not needed;
yet, complications arise when comparisons between different
size operations and changes in co-product production occur.
Selection of an allocation procedure can significantly influence
results and requires documentation.
Determining data requirements and quality constraints is
important. These requirements and constraints may constitute
the use of annual average values or evaluating specific instances
2
Photo courtesy of Pack Pix, NC State University.
of highly monitored events and the difference between using
database values versus monitored emissions (discrete or
continuous). The choice between publicly accessible data and
proprietary information is tied to the audience defined for the
LCA. In this light, internal business information may not be
appropriate for publicly disclosed results, and average national
data may not be suitable for internal reviews.
Preparing for properly formatted documentation and determining
the need for a critical review will expedite the production of
the final version of an LCA. Properly formatting the report can
legitimize the analysis and reduce time required for tedious
modifications. Depending on the goal, use of a third party for
conducting the LCA may be preferable to reduce the risk of bias;
otherwise, a critical review by a third party may be advisable.
Life Cycle Inventory Analysis
Compiling a life cycle inventory begins the process of assigning
emission values to operations within the boundary of the
system in question. Calculations will differ depending on the
source of data values, whether actual monitored data or an
inventory database of average values is utilized. Determination
of inventory values will also depend on whether the system
currently exists or is conceptual. Allocating process flows in
a uniform fashion is critical with most industrial operations
producing multiple products. It may be necessary to redefine
the system boundary during this step, which is typical, but
modifications need to be noted in the analysis. This need for
redefining the boundary may arise from data constraints (quality,
consistency, or availability), revised goals or scope, or any other
reasonable rationale with proper reporting. Calculations can
also include infrastructure emission values (e.g., lime production
for concrete) and indirect emissions (e.g., emissions from coal
mining for electricity production) depending on the defined
boundary. Many studies create an inventory with the average
emissions from unit operations, but it is also possible to look at
seasonal variations or focus on worst-case scenarios.
Life Cycle Assessment (LCA): Description and Methodology
Table 1. Select environmental impacts.
Category
Mid-point
End-point
Global Warming
CO2 equiv.
Temperature increase
Acidification
H+ mole equiv. or SO2 equiv.
Acid rain
HH Criteria
PM10 equiv. or PM2.5 equiv.
Human health
Eutrophication
N equiv.
Ecosystem loss
Ozone Depletion
CFC-11 equiv.
Human health
Smog
O3 equiv.
Human health
Ecotoxicity
PAF.m3.day or triethylene glycol equiv.
Ecosystem loss
Human Health (cancer/non-cancer)
Cases or chloroethylene equiv.
Human health
Jolliet et al. (2003), TRACI (2013)
Life Cycle Impacts Assessment
After compiling the life cycle inventory, an appropriate set of
impact factors are applied for impact aggregation. Two primary
categories of life cycle impact factors exist: mid-point and endpoint. Mid-point assessment methods are more scientifically
verifiable (Bare et al., 2000) and use a set standard of impact
category for a given inventory value, such as methane to carbon
dioxide (CO2) equivalents. The use of end-point impacts strives
to give an actual economic or environmental outcome to the
emissions. Although end-point assessment methods are well
formulated, they generally apply a number of assumptions that
deviate from measureable outcomes, such as an increase in
mean global temperature due to methane emissions. During
this step, it is possible to specifically categorize (e.g., human
health), spatially normalize (e.g., regionally or nationally), or
weight the impacts to determine a total LCA score. Use of these
standardization techniques is optional, will depend on the goal
of the specific study, and may incorporate additional uncertainty
into the analysis.
There are multiple environmental and human health impacts
associated with emissions, making it difficult to determine the
correct impact categories associated with the system being
assessed. A host of categories exist for related mid- and endpoints. Although it does not encompass all possibilities, Table 1
outlines some common impact factors.
Non-point source emissions and some impact categories may
be difficult to quantify. Accounting for land use (m2), water
use (L), waste disposal (kg), fossil fuel depletion (MJ), and
mineral depletion (kg) may be straightforward, but determining
the impacts associated with each of these categories is not.
Differentiating these emission values into distinct categories
can better account for the associated impacts (e.g., arable vs.
marginal land, tap vs. well water, and municipal vs. chemical
waste). Some published general values exist for non-point
sources, but these can vary greatly depending on differences in
Life Cycle Assessment (LCA): Description and Methodology
the characteristics and properties of the source. For example,
emissions from wastewater treatment lagoons can be influenced
by geographic location, influent, design, and many other factors.
In this regard, using generalized data for non-point sources can
be problematic. The temporal and spatial characteristics of an
emission can also influence outcomes. For example, land use
change from bioenergy production on a plot scale in the short
term may not repay the carbon stocks (Manomet, 2010), but
long-term observation (Lucier, 2010) shows the biogenic nature
of this energy source. The choice of impact factors included in
an LCA analysis can affect the results significantly.
During the impact assessment phase, spatial and temporal
effects that can modify the actual impacts of the analysis should
be taken into account. This is not a concern with mid-point
impacts since the emissions are standardized with regards to
a uniform emission standard, with no actual environmental
outcome being determined. Where those emissions take place,
whether they are point or non-point sources, and whether
specific thresholds are met to cause impacts are all important
factors when evaluating results. Variations in time of emission
can also affect actual impacts. Consider whether the emissions
are continual or intermittent and whether the time of the year or
day has an effect.
Life Cycle Interpretation
The interpretation portion of the analysis occurs continually
throughout the LCA process. Interpretation is the systematic
process of determining conclusions by identifying significant
issues, evaluating how well the data was compiled, and
compiling findings and recommendations within the guidelines
of the goals and scope. Despite the standardized structure of
the LCA framework, it is incredibly flexible in supporting a wide
range of goals and scopes.
3
CONDUCTING A LIFE CYCLE ASSESSMENT
A life cycle assessment can seem like a daunting task because
of the complexity of the many systems we find interest in,
especially with expanding system boundary size. It is important
to adequately prepare during the goal and scope step, but be
prepared for modifications as the analysis progresses, as is
permissible through interpretation. The previously outlined basic
methodology can fit a wide range of systems, with industry,
residential, government, academic, and commercial groups
having successfully used LCA methodology for both actual and
conceptual systems. This type of analysis is commonly utilized
for the comparison of system options whether for research,
system modifications, or construction.
The most prominent LCA software packages are Gabi (GaBi,
2013) and SimaPro (SimaPro, 2013). These programs are userfriendly impact calculators with various databases containing
equipment information, GHG inventories for standard operations,
and sets of impact factors. Process flows are constructed by the
user, and data can be modified by user preference. Depending on
specific system knowledge, modifications may not be advisable
since database values are referenced and changes may alter the
integrity of the calculations. Publicly available software, such as
the Greenhouse Gases, Regulated Emissions, and Energy Use in
Transportation Model (GREET, 2013), are useful but can contain
embedded assumptions that need to be understood, or modified,
to accurately model specified systems. Other methodologies,
such as the Economic Input-Output Life Cycle Assessment
(EIOLCA, 2013), are modified from the basic LCA framework but
may be sufficient depending upon goals and scope.
Though these programs can assist with the process, they are
not mandatory for developing an LCA. Following standard
methodology, proper accounting, and thorough record keeping/
reporting will ensure the legitimacy of the analysis. Process
information is available through various sources, including
process engineering software such as ASPEN (AspenTech,
2013), and values can also be obtained from many government
and research institution sources, many of which are freely
accessible. Inventory databases are also available from
commercial sources, such as Ecoinvent (Ecoinvent, 2013), and
publically available sources, such as the US Life Cycle Inventory
Database (US LCI, 2013). Specific process inventories are
available from various organizational entities, such as Glass
for Europe (Usbeck et al., 2011) and the American Chemistry
Council (ACC, 2011). Impact databases are also available
from commercial and public sources, such as the Tool for the
Reduction and Assessment of Chemical and other Environmental
Impacts (TRACI, 2013) and IMPACT 2002+ (Jolliet et al., 2003).
There are many other publicly and commercially available
resources for conducting an LCA, but it is important to ensure
that proper sources are utilized for the system to accomplish
specified goals.
It is common for some energy analysis publications to use the
phrases life cycle energy analysis, LCA energy, life cycle energy
audit, or similar statements. These analyses follow the basic
outline of an LCA but focus on energy as the major metric
of interest, not accounting for the environmental impacts
mentioned in Table 1 and many others. Many LCA publications
calculate energy values, and some also compare these to
economic evaluations of their specific system of interest.
Energy calculations are sometimes referred to as energy audits
and economic evaluations may be termed technoeconomic
evaluations, or some variation of these.
A basic understanding of how these studies are conducted
is imperative to determine how applicable the results are to
a specific system. LCA calculations are made with specific
parameters and production scenarios in mind, and the results do
not always apply when the system operations and impacts are
modified. The true strength of an LCA is the total accounting of
environmental impacts related to a specific system to determine
areas for process improvements, create baseline data, or
compare system alternatives.
LCA PROCESS EXAMPLE: GRAIN PRODUCTION
FROM MAIZE
Corn grain production in North Carolina was chosen as
an example system for practical application of the LCA
methodology. With different system boundaries and input
values, final impact values could have been significantly
Photo by Warren Gretz, NREL 10460.
4
Life Cycle Assessment (LCA): Description and Methodology
modified. The example discussed here can be used as a basic
framework and was designed to represent minimum-till corn
grain production in eastern North Carolina. It is important to
note that production systems can change with factors such as
soil type, management strategies, annual/seasonal weather
patterns, available equipment, location, previous land use, and
other associated factors.
Goal and Scope Definition
Goal
The goal of the study was to serve as an example of how the
LCA analysis procedure can be used to determine environmental
impacts (example impacts shown in Table 1), specifically in
relation to the production of corn grain (maize) in eastern North
Carolina. This analysis was developed for public use as an
example for individuals interested in the LCA methodology.
Scope
Table 2 outlines various parameters related to the scope of the
analysis. Most thorough, professionally conducted LCA analyses
follow some specified reporting format with a significant amount
of boilerplate included.
The specific system of interest was production of corn grain
in eastern North Carolina with a functional unit of one bushel
(56 pounds). This system followed the growth cycle of corn,
accounting for associated inputs and use of a single iteration
method for indirect emission sources (detailed in the Life Cycle
Inventory Analysis section).
Table 2. Scope parameters for grain production from maize in
eastern North Carolina.
Scope Items
Parameters
System Product
Corn grain
System Function
Production of corn grain
Functional Unit
Bushel
System Boundary
On farm
Allocation Procedure
Single product
LCIA Methodology
TRACI (limited impacts)
Interpretation
Continual
Data Requirements
North Carolina/United States
Assumptions
Various
Value Choices/Optional
Elements
None
Limitations
Various
Initial Data Quality
Publically available
Critical Review
Not needed
Type/Format of Report
NC Extension Publication
Life Cycle Assessment (LCA): Description and Methodology
Figure 1. Corn grain LCA system boundary.
A system boundary was set around all farm operations
terminating at grain elevator delivery (Figure 1). A minimumtillage crop management strategy was employed with relatively
high grain yields for eastern North Carolina (160 bushels per
acre). Acquisition of raw materials and processing data were
included from publicly accessible sources.
A number of processes were not selected for inclusion in
the system boundary: land use change (direct and indirect),
equipment manufacture, seed production, and storage losses.
The study excluded land use changes from the system boundary
due to the inconsistency of land use change metrics; however,
it did account for arable land. Since continual agricultural use of
the field was assumed, land use change may be accounted for
as zero. Equipment manufacture was not included because of
the lack of specific publicly available data. Generalized sets of
raw material inputs for equipment manufacture are available,
such as Heller et al. (2003), but inconsistencies existed between
manufacturing operations and specific equipment. Seed
production was not accounted for due to the lack of knowledge
of seed stock production techniques, which is commonly
genetically modified in the United States. Storage losses
were assumed to be zero, resulting from proper grain drying
and limited storage time. Decomposition, however, can cause
additional environmental impacts, especially from high moisture
grain. Changes in soil carbon stock and resulting emissions were
not included because a minimum-tillage strategy was used to
maintain or increase soil carbon. Finally, agrochemical runoff and
volatilization were not considered in this analysis because of the
site-specific nature of these parameters. If specific information
were available on chemical fate-transport with detailed site
5
as a publicly available database normalized for the United
States. Though the TRACI database consists of a wide range of
impact categories, only select impacts (Table 3) were used in
this analysis. No additional normalization, grouping, or weighting
took place.
Table 3. Select mid-point impact categories.
Mid-Point Category
Unit
Air Emissions
Global Warming
CO2 equiv.
Acidification
H+ mole equiv.
HH Criteria
PM10 equiv.
Eutrophication
N equiv.
Ozone Depletion
CFC-11 equiv.
Smog
O3 equiv.
Water Emissions
Eutrophication
N equiv.
Waste
Solid Waste—Landfill
Figure 2. Corn grain raw material flows for agrochemicals, soil
additives, and fuel acquisition and manufacturing.
information, runoff and volatilization may be an important
parameter to include.
Acquisition, manufacture, and use of raw materials were
included within the system boundary (Figure 2). Impacts of
agrochemicals (herbicides) and potassium were determined from
energy use values only. Agrochemicals were evaluated this way
because of the proprietary nature of their production, making
publicly available data scarce. Although they were not outlined
in Figure 2, raw material process flows within the electricity
boundary included energy production and use from coal, nuclear,
fuel oil, and biomass.
This simplified example system had only a single material
considered as an output (corn grain), so an allocation procedure
was not required. It was possible to consider some additional
products, such as corn cobs and stover, at the farm. These
residues have been proposed for use in bioenergy production,
and there are some niche markets available, such as animal
bedding and feed, that may have been incorporated in the
system, if warranted. For this LCA, the residues were not part of
the system described.
A mid-point assessment approach was utilized to determine
impacts for this LCA analysis. The US Environmental Protection
Agency’s (EPA) Tool for the Reduction and Assessment of
Chemical and Other Environmental Impacts (TRACI) was chosen
6
Waste
For the interpretation section, the results of this simplified LCA
were compared with other analyses of corn grain production
systems. The comparison was difficult because other studies
had varied results from differences in system boundary,
inputs, and all other aspects of the analysis. Other aspects of
interpretation took place throughout the LCA analysis to update
and modify values as warranted.
A data quality requirement was established for using the best
publicly available data to allow for ease in duplication of results,
which is not as straightforward when using proprietary data.
Data inputs focused on values from North Carolina, followed
by the southeastern United States, the entire United States,
and finally, global averages. A major weakness of using publicly
available data as a data source is the need to make some
generalizations.
A number of assumptions were used in the LCA analysis,
including:
• Average field acreage for eastern North Carolina
• Uniform emission values
• No annual or seasonal variation
• Production of lubricants was similar to residual fuel oil
• Tractor trailer assumed to get 6 miles to a gallon, 1000 bushel
capacity
• Lime use calculated from nitrogen use and type (1.97 times
nitrogen addition)
• Corn seed weight of 1200 seed per pound
• Yield of 160 bushel per acre at 18% moisture content (wet
basis)
Life Cycle Assessment (LCA): Description and Methodology
Table 4. Equipment fuel and lubricant use.
Operation
Type
Power Unit
Fuel—Diesel (gal/ac)
Lubricant—Residual Fuel Oil (gal/ac)
0.57
0.0164
Tillage
Field Aerator
110-128 PTO HP
Pre-Emergent Herbicide
Boom Sprayer
50-59 PTO HP
0.1
0.0029
Nutrient Application
Fertilizer Spread x2
30-39 PTO HP
0.15 (x2)
0.0043 (x2)
Planting
Four-row Planter (min-till)
110-129 PTO HP
0.53
0.0153
Post-Emergent Herbicide
Boom Sprayer
30-39 PTO HP
0.15
0.0043
Nutrient Application
Fertilizer Spreader
30-39 PTO HP
0.15
0.0043
Harvesting
Combine, Grain Head
None
1.49
0.043
In-Field Transportation
Grain Wagon
30-39 PTO HP
Loading/Unloading
Grain Elevator x2
Drying
70-89 PTO HP
Grain Dryer
Transportation
Five Axle Semi
Combination
Grain Trailer
Table 5. Use parameters on an acreage basis.
Operation
Herbicide
Soil Nutrients
Seed
Yield
Transportation
Fuel Use
Lubricant
Type
0.2
0.004
Fuel—Diesel (gal/bu)
Lubricant—Residual Fuel Oil (gal/bu)
0.0043 (x2)
0.0003 (x2)
Fuel—Electricity (kWh/bu)
(per 1% to 15.5%)
Fuel—LP Gas (gal/bu) (per 1% to
15.5%)
0.01
0.02
Fuel Use
Lubricant—Residual Fuel Oil (gal/bu)
Included in Transportation
8.33 X10 -6
Table 6. Sources of input values.
Value
Unit
Glyphosate
1.38
lb/ac
1.18
lb/ac
Equipment Fuel
Requirements
Lazarus, 2009; Hanna, 2005
Atrazine
Paraquat
0.5
lb/ac
Field Capacity
Lazarus, 2009; Hanna, 2001
Nitrogen (N solution)
160
lb/ac
Lubrication Use
USDA, 2005; Edward, 2009
Phosphorus (P 2O5)
50
lb/ac
Fertilizer Use
NCSU, 2013
Potassium (K 2O)
100
lb/ac
Dryer Fuel Use
NCSU, 2013
Lime (spread)
315.2
lb/ac
Herbicide Use
USDA, 1999
Hybrid GMO Seed
24.375
lb/ac
Seeding Rate
KSU, 2013
160
bu/ac
Transportation
USB, 2012
546.56
ton-mi/ac
Fertilizer Statistics
USDA, 2011
Long Haul (250 mi)
118.39
ton-mi/ac
Diesel
4.8613
gal/ac
LP Gas
8
gal/ac
Electricity
4
kWh/ac
0.3644
gal/ac
18% MC (wet basis)
Short Haul (61 mi)
Residual Fuel Oil
The LCA report was formatted as a North Carolina Extension
Service publication. Enough information was provided about
the analysis to be informative without much of the boilerplate
included in many professional LCA reports. A specific critical
review was not deemed necessary, but the publication was peer
reviewed by a number of scientists in the field.
Life Cycle Inventory Analysis
Microsoft Excel was used to calculate inventory values of
material inputs for equipment use (Table 4) and commodity
inputs (Table 5). Any values not referenced in Table 6 came
Life Cycle Assessment (LCA): Description and Methodology
Area
Source
from production knowledge and general trends for corn grain
production in eastern North Carolina.
The US Life Cycle Inventory Database (US LCI, 2013) was used
to convert commodity products into subsequent emissions along
their life cycles. The database consisted of a number of modules
from varying sources appropriate for the United States. Some
of these modules integrated all aspects of production (e.g., fuel
use, transportation, and inputs) while others did not; information
on the inclusion of these factors was provided in each module.
The integration of modules to produce nitrogen fertilizer is
shown in Table 7, including manufacture and raw material
acquisition. After these values were compiled, a decision on
energy use and transportation accounting was required.
For this analysis, a single iteration approach was used to
calculate emissions related to energy use and transportation.
7
Table 7. Category summation for nitrogen fertilizer (abridged).
Nitrogen Fertilizer,
production mix, at
plant
Natural Gas,
processed, at plant
Natural Gas, at
extraction site
Nitrogen Fertilizer,
total
Inputs
Natural Gas, processed, at plant (cu ft)
15.14997458
Natural Gas, at extraction site (cu ft)
1.028
Gas, natural (cu ft)
1
Output
Nitrogen Fertilizer, production mix, at plant (lb)
1
1
Natural Gas, processed, at plant (cu ft)
1
Natural Gas, at extraction site (cu ft)
1
Air Emissions
Ammonia (lb)
0.000405
0.0000405
BTEX, unspecified ratio (lb)
Carbon Dioxide, fossil (kg)
0.0000158105
0.531
0.531
Carbon Monoxide, fossil (lb)
0.000035
Methane, fossil (lb)
0.000215
0.000035
0.0000864313
Sulfur dioxide (lb)
VOC, volatile organic compounds (lb)
0.00024
0.000045
0.000550002
0.01009
0.001118832
0.01695
0.000035326
0.00058
Water Emissions
Barium (lb)
0.0000563005
0.000877
Bromide (lb)
0.0000423866
0.00066
Chloride (lb)
0.007147986
0.111324
0.00012538
0.001953
Suspended Solids, unspecified (lb)
Energy Use
Bituminous Coal, combusted in industrial boiler (lb)
0.0081
0.0081
Diesel, combusted in industrial boiler (gal)
0.00000712736
Dummy, Energy, unspecific (btu)
313.7278021
Electricity, at grid, US, 2000 (kWh)
0.022992625
0.0001142
313.7278
Gasoline, combusted in equipment (gal)
0.000444914
0.00081391
0.0424091
0.000000262446
0.00000379359
0.00006303
0.025471
0.024149
0.7619839
0.000000273248
0.00000439996
0.00007261
Natural Gas, combusted in industrial boiler (cu ft)
Residual Fuel Oil, combusted in industrial boiler (gal)
Transportation
Transport, combination truck, average fuel mix (tm)
0.063501104
Transport, train, diesel powered (tm)
0.192501024
0.0635011
0.192501
Disposal
Dummy, Disposal, chemical waste, unspecific, to
sanitary landfill (lb)
0.00009
0.00009
Dummy, Disposal, inert solid waste, to inert material
landfill (lb)
0.00009
0.00009
Dummy Disposal, solid waste, unspecified, to
unspecified treatment (lb)
8
0.001199988
0.018689
Life Cycle Assessment (LCA): Description and Methodology
Table 8. Corn grain life cycle inventory (abridged)
Acreage
Basis
Table 9. Nutrient volatilization and leaching.
Air emissions
Ammonia (lb)
0.12525288
0.00078283
BTEX, unspecified ratio (lb)
0.05094403
0.0003184
Carbon Dioxide, fossil (lb)
1124.21489
7.026343079
Carbon Monoxide, fossil (lb)
37.9822858
0.237389286
Methane, fossil (lb)
12.8342917
0.0802143423
Sulfur dioxide (lb)
5.3580089
0.033487556
0.25564946
0.001597809
VOC, volatile organic compounds (lb)
Water Emissions
Barium (lb)
12.6633133
0.079145708
Bromide (lb)
2.31780541
0.014486284
Chloride (lb)
390.71787
2.441986689
28.4279578
0.177674736
Dummy, Disposal, chemical waste,
unspecific, to sanitary landfill (lb)
0.0143997
0.0000899998
Dummy, Disposal, inert solid waste, to
inert material landfill (lb)
0.0143997
0.0000899998
Dummy Disposal, solid waste,
unspecified, to unspecified treatment
(lb)
12.9500201
Suspended Solids, unspecified (lb)
Acreage Basis
Bushel Basis
N2O (lb)
0.196
0.0012
N2 (lb)
1.96
0.0123
NO3 (lb)
1.764
0.011
0.294
0.0018
NH3 (lb)
Phosphorous
P (lb)
85.658
First, all inputs were taken into account, similar to Table 7, and
the total energy use and transportation values were calculated.
Next, all energy and transportation emission values from
the category summation were included as direct emissions,
disregarding the associated energy use and transportation
values of these embedded emissions, and thus halting a
continual loop at a single iteration. This process created a
database of life cycle emissions related to each product and
operation. It was possible to use a multiple iteration procedure,
since transportation and energy use are embedded in their
own production, but a single iteration approach was deemed
adequate for this analysis. Creating a life cycle inventory
database compiled in a spreadsheet was a long and tedious
process, but LCA software packages do this automatically (US
LCI modules are able to be used within most major software
packages).
Use of other LCI resources may be advisable when a single
database either does not contain, or has limited information on,
a specific input. For this analysis, energy use data from Shapouri
et al. (2002) was used for herbicide and phosphorous production.
These energy values were given emissions related to energy
values computed in the single iteration LCI process outlined
above. This method disregards extraction and processing
Life Cycle Assessment (LCA): Description and Methodology
0.5354
Table 10. Global warming impact related to corn grain
production (abridged).
Bushel Basis
Disposal
0.080937626
Bushel Basis
Nitrogen (N)
Global
Warming
Impacts
(lb CO2
equiv./lb.)
Global
Warming
(lb CO2
equiv.)
1
7.026343079
25
2.005358075
Air emissions
Ammonia (lb)
0.000725973
BTEX, unspecified ratio
(lb)
0.003184
Carbon Dioxide, fossil
(lb)
7.026343079
Carbon Monoxide, fossil
(lb)
0.237389286
Methane, fossil (lb)
0.0802143423
Sulfur dioxide (lb)
0.033487556
VOC, volatile organic
compounds (lb)
0.001597809
Water Emissions
Barium (lb)
0.079145708
Bromide (lb)
0.014486284
Chloride (lb)
2.441986689
Suspended Solids,
unspecified (lb)
0.177674736
Disposal
Dummy, Disposal,
chemical waste,
unspecific, to sanitary
landfill (lb)
0.0000899998
Dummy, Disposal, solid
waste, unspecified, to
sanitary landfill (lb)
0.57310972
Dummy Disposal, solid
waste, unspecified, to
unspecified treatment
(lb)
0.080937626
Total Global Warming
Potential (lb CO2 equiv.)
9.031701154
9
emissions related to these commodities but was a better option
than excluding these processes entirely.
Using the emission database produced with the single iteration
method from the US Life Cycle Inventory Database (US
LCI, 2013) and the use values given in Table 5, the life cycle
emissions were determined on an acreage and bushel basis,
with an abridged list of emissions shown in Table 8.
Nitrogen emission values were calculated from Lammel (2000),
converted from ammonia nitrogen, and phosphorous leaching
values were used from Siegerist and Pfister (2013) (Table 9).
Life Cycle Impact Assessment
The Tool for the Reduction and Assessment of Chemical and
Other Environmental Impacts (TRACI, 2013) was used to
determine mid-point impacts. Table 10 shows an example of the
calculation process related to global warming potential.
A series of environmental impacts were calculated for the
total system (Table 11). For this analysis, no normalization or
weighting factors were used to aggregate impacts.
Table 11. Environmental impacts related to corn grain
production (bushel basis).
Mid-Point Category
Value (lb/bushel)
Unit
Air Emissions
Global Warming
7.2
CO2 equiv.
Acidification
2.6
H mole equiv.
HH Criteria
4.9 x 10
Eutrophication
8.4 x 10 -4
N equiv.
Ozone Depletion
1.6 x10
CFC-11 equiv.
Smog
+
-3
-8
0.46
PM10 equiv.
O3 equiv.
Water Emissions
Eutrophication
0.23
N equiv.
Waste
Solid Waste- Landfill
0.65
Waste
Interpretation
Values published by Kim et al. (2009) were converted for direct
comparison with the impacts determined in this example (Table
12). Using ammonia as a reference impact, categories were
modified to the impact categories used in this analysis between
the TRACI Database (TRACI, 2013), acidification (Jolliet et al.
2003), and eutrophication (GHK, 2006).
The acidification and eutrophication values from this example
(Table 11) were slightly higher than the overall values calculated
from Kim et al. (2009) (Table 12) but were relatively similar. The
global warming values were considerably lower in this study,
10
Table 12. Average comparative environmental impacts (bushel
basis). (Kim et al., 2009)
Overall
Agrochemicals
Field
Field
Operations Emissions
lb CO2/bushel
Global
Warming
23.70
6.08
3.16
14.46
0.14
1.36
0.01
0.15
lb H+/bushel
Acidification
1.91
0.42
lb N/bushel
Eutrophication
0.18
0.02
but the values in Kim et al. (2009) take into account tillage
operations (field emissions of Table 12). When this difference
was taken into account, the global warming values were
relatively similar. When trying to compare two different LCA
studies using different system boundaries, functional units,
input values, and other characteristics, it is common to observe
variations.
CONCLUSION
This publication should be used as a tool to help the public
understand the process behind life cycle assessment
methodology. The included example is meant for educational
purposes to highlight the possibilities of using LCA to account
for more than carbon and the opportunities to add complexity
by altering system boundaries. Modification to the goals and
scope of the system described here can potentially cause
significant differences in results. Nevertheless, life cycle
assessment provides a systematic process for determination
of environmental impacts throughout a product life cycle
and continues to provide worthwhile insight for improving
environmental stewardship.
ACKNOWLEDGEMENTS
The authors would like to acknowledge former North Carolina
Extension Specialist Dr. Matthew W. Veal, Ph.D. for his
innovation and leadership in development of this publication.
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The following resources were used in the publication of this
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11
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Prepared by
Kevin R. Caffrey, Graduate Research Assistant
Mari S. Chinn, Associate Professor
Biological and Agricultural Engineering,
North Carolina State University
Published by
North Carolina Cooperative Extension Service
Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial
products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned.
Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain
current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.
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