Environmental impacts comparison between on-site vs. prefabricated just-in-time (prefab-JIT) rebar supply in construction projects.
Kim, Yong-Woo ; Azari-N, Rahman ; Yi, June-Seong 等
Introduction
Construction industry is one of the largest industries and at the
same time among the industries which cause highest levels of pollution
(Horvath 2004). Over the recent decades, the natural environment has
gained increasing importance to construction firms and many contractors
have started to realize their impacts on the environment and take
actions to reduce them.
The growing body of literature addressing the environmental impacts
of construction industry demonstrates the importance of the issue. A
survey of existing knowledge in the field shows various attempts to
assess the environmental life cycle impacts associated with construction
materials and buildings (Koch 1992; Buchanan, Honey 1994; Meil 1994;
Junnila, Horvath 2003; Petersen, Solberg 2005; Gustavsson et al. 2006;
Gillespie et al. 2007; Werner, Richter 2007; Bribian et al. 2011). The
focus in most of the literature is on the life cycle impacts of specific
building materials. These studies, however, either fail to include the
environmental impacts of the material delivery systems or simply use
rough approximations which, in most cases, do not match the reality. The
main reason for this has to do with the complexity of delivery systems
as well as the limitations associated with applied methodologies.
Reinforced steel bars are important components in the construction
of contemporary commercial buildings, and their type of delivery is
considered a critical factor in meeting the budget and schedule targets
(Polat, Ballard 2003). Traditionally, the construction industry has used
a delivery system in which rebars are delivered from the supplier's
facility or the contractor's warehouse to the construction site in
large batches. Rebars are then fabricated (i.e. cut and bent) on-site
and positioned for assembly. Due to the large on-site yard areas and the
holding costs needed in this system, a new rebar delivery system
inspired by lean principles has started to gain attention in the
industry. The new system which can be called prefab-JIT [prefabrication
with Just-In-Time (JIT) delivery] applies off-site cut and bend (i.e.
prefabrication) of rebars along with frequent delivery of them in small
batches as needed over the construction process. Although the new system
requires more frequent delivery of rebar batches, it omits the on-site
yard space requirements as well as the delivery within the construction
site (i.e. on-site yard to building).
Arbulu and Ballard (2004) showed that this lean delivery system
improves productivity due to prefabrication. While this study and most
of other relevant research regarding delivery systems focus on how to
reduce the lead time using process improvements (Arbulu et al. 2003;
Akel et al. 2004; Kim et al. 2007), they often ignore the environmental
life cycle impacts of the systems.
This paper intends to assess and compare the environmental impacts
of two rebar delivery systems, including the traditional system (on-site
fabrication along with large batch delivery) and the prefab-JIT system,
in a case study construction project using a process-based
cradle-to-gate life cycle assessment (LCA) methodology. To do this, the
goal and scope of the project are first defined. Then, an inventory
modeling is performed by identifying the unit processes of the two
systems and tracking and quantifying the environmental (material,
primary energy, air emissions, etc.) and economic flows (transportation,
electricity, etc.) associated with the unit processes. At the next
phase, contributions of the two systems to the environmental impact
categories are assessed. Impact categories of interest include
acidification, eutrophication, global warming, and smog formation.
Finally, the authors interpret the LCA results and identify the critical
factors affecting the environmental impacts of the two systems.
The case study used for the study of the prefab-JIT delivery system
is a high-rise condominium construction project located in downtown
Seattle, USA, where the system has actually been applied. The rebar
delivery occurs from a rebar prefabrication plant in Tacoma, USA, to the
location of the case study project in Seattle, USA.
The model for traditional rebar delivery system in this study was
hypothetically modified from the prefab-JIT delivery system used in the
case study. For the traditional rebar delivery system, the rebar
products were assumed to be delivered on the construction site in large
batch sizes and to be fabricated on-site.
The application of the traditional system and the prefab-JIT
delivery system in the case study implies differences in equipment use,
transportation distances, rebar loss rate, etc. between the two which
will be explained later in this paper.
1. LCA methodology
LCA is a quantitative approach for assessing what energy sources
and materials and in what quantities are used and/or wasted throughout
the life cycle of a product or system. A full life cycle spans the raw
material extraction, material processing, product manufacturing,
operation and maintenance, and finally disposal and material recovery
activities. The quantities of needed transportation between these
processes as well as the required fuels are also considered in life
cycle assessments.
To assess the environmental life cycle impacts of the two rebar
delivery systems, we implemented the process-based cradle-to-gate LCA
methodology according to ISO 14040:2006 and ISO 14044:2006 standards.
The methodology addresses four major phases in its assessment including
the goal and scope definition, inventory modeling and analysis, impact
assessment and interpretation of the results. The outcome would be an
LCA study which is ISO 14040 series compliant.
The inventory model for each delivery system was developed using a
variety of data sources to ensure the quality of data and to fill the
data gaps. In each model, the life cycle energy use (fossil, petroleum,
coal, natural gas, diesel, electricity, and propane) and air emissions
contributing to global warming, photochemical smog, acidification, and
eutrophication were tracked and quantified. Then, contributions to the
impact categories were assessed and the results of the two models were
compared and interpreted.
2. Goal and scope definition
The goal and scope definition, as the first phase of LCA
methodology, addresses issues such as the intended audience, intended
application, functional unit (FU), system boundaries, etc.
The intended audiences of this study are researchers who intend to
investigate the environmental impacts of construction processes
including material delivery systems. The study also targets general
contractors, subcontractors, and rebar prefabrication plant managers.
The results can be used to advance the understanding of the
environmental impacts associated with alternative delivery systems and
to inform the construction industry practitioners of the systems with
less impact on the environment.
2.1. Function and FU
The system function of this LCA project is the production and
delivery of raw rebar, as well as fabrication, assembly, transportation,
and installation of rebar products on the construction site.
The FU, a measure of the functional output of the systems to be
quantified, is the installation of 80,000 kg of rebar assemblies on the
construction site in downtown Seattle, USA, over one week.
2.2. System boundaries
The system boundaries of the two rebar delivery systems cover the
unit processes that are associated with raw material extraction,
processing, raw rebar manufacturing at a mill plant, fabrication and
assembly of rebars, and installation of the fabricated rebars on the
construction site. It will also include the unit processes of the energy
sources used within the system boundaries as well as the transportation
of materials between the unit processes. Moreover, for a better
representation of the practice in reality, the backhauls of
transportation loaded with material scraps from the construction site
are considered in both systems. Due to the lack of resources and data,
however, the supply chains after installation of the rebar products are
not included in this cradle-to-gate LCA study. Figures 1 and 2 show the
system boundaries of the two delivery systems.
3. Inventory modeling and analysis
The "inventory modeling and analysis" is the second phase
in the LCA methodology in which the environmental inputs and outputs of
the unit processes are tracked and quantified and then, the aggregate
environmental flows for the whole system boundaries are calculated.
As stated in the introduction section, the two rebar delivery
systems that are studied in this paper include (1) traditional system:
on-site fabrication along with large batch delivery, and (2) off-site
fabrication (prefabrication) with JIT delivery. The authors investigated
the economic and environmental flows associated with application of the
two rebar delivery systems at a high-rise condominium construction
project in downtown Seattle, USA, from the production of raw rebars to
the installation of the rebar cases.
The information about overall rebar processing steps and
activities, main equipment use, the energy types and quantities
consumed, distances of material transportation, frequency of delivery,
and other qualitative information was collected mainly through
documentations of the case study project, interviews with the key
personnel (project engineers, material procurement managers, general
contractor, etc.) at the prefabrication plant, assembly yard and on the
construction site, as well as through direct observations.
The documentations of the case study construction project were
investigated for tracking the actual data related to the prefab-JIT
delivery. The traditional rebar delivery system was then designed based
on the modification of the prefab-JIT system used at the case study
project. The information needed for the traditional system was built
through investigation of literature, interviews with the general
contractor, project engineers and the suppliers as well as the
authors' calculations.
The study of the application of the two systems in the case study
revealed that they vary over certain key operational issues. The main
differences between them are summarized in Table 1.
3.1. Rebar fabrication and assembly process
A major difference between the two delivery systems has to do with
the rebar fabrication and assembly process. As a result of this
difference, the equipment type, capacity, and their operating time would
be different in the two systems. The equipment productivity and energy
consumption per ton of rebar in traditional on-site fabrication system
were realized to be lower than those in the prefab-JIT system:
--Traditional delivery system. In traditional system, as shown in
Figure 1, rebars are delivered from mill plant to the construction site
where they are fabricated, assembled, and installed. Tower cranes, rebar
benders/ cutters, and forklifts are the equipment utilized on the
construction site to perform the needed processes;
--Prefab-JIT delivery. In prefab-JIT delivery, as shown in Figure
2, rebars are delivered from mill plant to a prefabrication plant where
rebars are fabricated and partially assembled. Then, when needed on the
construction site, they are transported to the site location where they
are installed. In this system, traveling overhead cranes, rebar
benders/cutters, and forklifts are used at the prefabrication plant
rather than on the construction site. Although the rebar benders/cutters
are commonly used in both the on-site and off-site systems, the machine
capacities would be different. The offsite plant uses a larger capacity
bender/cutter for a lesser operating time compared with the one at the
on-site temporary plant.
[FIGURE 1 OMITTED]
3.2. Delivery distance
The delivery distance influences the delivery time and thus, the
fuel consumption and air emissions:
--Traditional delivery system. It was assumed that the rebar
supplier, located in Tacoma, USA, delivered raw rebars directly to the
construction site in Seattle, USA, which is 27 miles away from the
supplier;
--Prefab-JIT delivery. The rebar supplier, located in Tacoma, USA,
delivered the raw rebars to the rebar fabrication plant in Tacoma, USA,
using heavy-duty trucks. The distance between the two facilities is 5
miles. After fabrication of the rebars at the prefabrication plant, they
are delivered to the construction site which is 27 miles away from the
plant. The total delivery distance in this system is 32 miles.
[FIGURE 2 OMITTED]
3.3. Rebar loss rate
Different rebar loss rates for the two systems affect the amount of
rebar wastes and the rebar product reproduction. Although the estimated
needed rebar quantity for the case study was 80,000 kg, the project
engineer ordered additional 3% of raw rebars in the prefab-JIT system
which accounted for an order of 82,400 kg of rebars. The study revealed
that the rebar loss rate in traditional system is 10% which accounts for
a final order of 88,000 kg of rebars in this system. Different rebar
loss rates in the two systems imply different additional equipment
working hours that were considered in the modeling.
3.4. Batch size
The number and the size of the rebar batches directly influence the
frequency of the rebar delivery which, in turn, affect the working time
of the applied equipment and subsequently, their energy use. The
delivery truck capacity for the two systems, however, was assumed to be
the same: 25 tons. The batch sizes of the rebar products in traditional
system and in prefab-JIT system were 25 and 21 tons, respectively.
Finally, the inventory databases were used for tracking and
quantifying the environmental flows of the unit processes within the
system boundaries. These databases include:
--Greenhouse Gases, Regulated Emissions, and Energy Use in
Transportation (GREET), provided by Department of Energy (DOE), USA
(GREET Database 2011);
--Tool for the Reduction and Assessment of Chemical and other
environmental Impacts (TRACI), provided by Environmental Protection
Agency (EPA), USA (TRACI 2011);
--NONROAD emissions model, provided by Environmental Protection
Agency (EPA), USA (NONROAD Model 2011).
The sources of the data for various unit processes within the
system boundaries of the two delivery systems are shown in Table 2.
3.5. Calculation procedures
The inventory analysis in this LCA study was conducted using the
methodology introduced by Heijungs and Suh (2002). According to the
method, the inventory vector as the outcome of the inventory analysis is
calculated through the equation:
[g] = [B] x [[A].sup.-1] x [f], (1)
where: g--inventory vector; B--intervention matrix;
[A.sup.1]--inverse matrix of technology matrix, and f--final demand
vector.
To do the inventory analysis, an Excel spreadsheet was created for
each delivery system. The inventory data for each system was separated
into a technology matrix (A) and an intervention matrix (B). The
technology matrix is a square matrix consisting of the economic flows
which represent the unit processes within the system boundaries of each
delivery system. The technology matrix was composed of all the key unit
processes required to generate energy, to produce, fabricate and
assemble the raw rebars, and install the rebar assemblies, and to
transport the rebar products to the case study construction
project's location in Seattle.
The intervention matrix represents the environmental flows
associated with the economic flows. Since the environmental impact
categories of interest in this LCA study were selected to be
acidification, eutrophication, global warming, and smog formation, the
environmental flows considered in this research are in fact the major
air emissions affecting the impacts categories. These emissions include
carbon dioxide (C[O.sub.2]), carbon monoxide (CO), methane (C[H.sub.4]),
nitrogen oxides (N[O.sub.X]), nitrous oxide ([N.sub.2]O), nonmethane
volatile organic compounds (NMVOC), and sulfur oxides (S[O.sub.X]).
It should be noted that the data presented in the technology and
intervention matrices are not scaled in this method to represent the
flows for the unit (1 kg) of rebar but instead, the data are entered in
a way to represent the flows associated with the unit quantity of each
unit process. Scaling is then conducted through a part of the equation
above. Specifically speaking, it is done by multiplying the inverse of
the technology matrix by the final demand vector (f) which represents
the set of economic flows that correspond to a reference flow; the only
nonzero element in the final demand vector.
Finally, g vector which represents the system-wide aggregated
environmental flows and is used for the impact assessment was calculated
through the Equation (1).
3.6. Inventory results
The results of the inventory modeling of the two rebar delivery
systems from the material extraction through rebar generation to the
installation of the rebars are shown in Table 3. The values represent
aggregated quantity of specified air emissions produced as a result of
activities defined by the system boundaries.
4. Impact assessment
The impact assessment phase of an LCA study deals with the
assessment of contributions of the environmental outputs (which is shown
through the inventory results) to the environmental impact categories.
Classification and characterization are the essential phases of this
phase in the LCA methodology.
4.1. Classification
In classification, the focus is on assigning the environmental
outputs to the appropriate environmental impact categories including
acidification, eutrophication, global warming, and smog formation. The
environmental outputs shown in the inventory result (Table 3) are
assigned to the impact categories as indicated in Table 4. As the table
shows, some air emissions contribute to more than one impact category.
4.2. Characterization
In characterization, the quantities of the environmental outputs
are multiplied by a characterization factor to achieve the contribution
of each environmental output to the impact category of interest.
Characterization factors are weighting factors assigned to the
environmental outputs to aggregate their contribution to a specific
environmental impact category into a score. Characterization factors for
this study were provided by TRACI (2011) database.
Table 5 shows global warming potential (GWP), acidification
potential (AP), eutrophication potential (EP), and smog potential (SP)
for the two delivery systems.
5. Interpretation
The interpretation phase in LCA methodology deals with the
explanation of the impact assessment results and the analysis of their
implications. In the case of this study, contributions of the two
delivery systems to the impact categories of study are compared and
interpreted. Also in this phase, the limitations of the LCA study are
highlighted and the recommendations with respect to overcoming those
limitations are made.
5.1. Global warming
Global warming is the increase in average temperature on earth
surface caused by greenhouse gas emissions (Eyerer et al. 2010). The
phenomenon can result in sea level rise, changes in rainfall patterns as
well as impacts on living species. GWP is measured in kg C[O.sub.2]
equivalent.
According to Table 5 and Figure 3, the air emissions resulting from
the delivery of rebars in the traditional system cause 8.36% higher
contribution to the global warming, compared with the air emissions in
the prefab-JIT delivery system. In both systems, carbon dioxide and
methane, respectively, are major drivers of GWP. The contribution to
global warming in both systems is caused mainly by the use of
diesel-powered equipment and raw rebar production.
5.2. Acidification
Acidification is the ongoing decrease in the pH value of rainwater
and fog which mainly results from the air pollutants transforming into
acids (Eyerer et al. 2010). It is usually measured in hydrogen ion
([H.sup.+]) mole equivalent or in kilogram sulfur dioxide equivalent.
The LCA results in Table 5 and Figure 3 show that the traditional
rebar delivery system compared with the prefab-JIT delivery system makes
a 6.96% larger contribution to acidification. Nitrogen oxides and sulfur
oxides are main contributors to this phenomenon in the two systems,
respectively. Similar to the global warming category, the contribution
to acidification in both systems results mainly from the use of
diesel-powered equipment and raw rebar production.
5.3. Smog
Smog formation is caused when the pollutants that are discharged
from industry and transportation into the atmosphere react with sunlight
(Ibanez 2007). The result is damage to the human health, plants, and
animals. Nitrogen oxides are important elements in development of
photochemical smog.
[FIGURE 3 OMITTED]
As Table 5 and Figure 4 show, the traditional rebar delivery system
causes a larger contribution of 6.65% to smog formation compared with
the prefab-JIT system. Also, the results show that Nitrogen oxides and
volatile organic compounds (VOCs), respectively, are major contributors
to smog formation in both systems.
5.4. Eutrophication
Eutrophication is defined as the process in which the water bodies
become more productive as a result of the increased input of inorganic
nutrients (Welch, Jacoby 2004). The outcome of this process is
burgeoning growth of algae in the water which blocks sunlight from
reaching lower levels of the sea (Eyerer et al. 2010).
Comparison of the LCA results between the two rebar delivery
systems shows that 6.65% more contribution to eutrophication is caused
as a result of delivery of rebars in the traditional system compared
with their delivery in the prefab-JIT system (Table 5 and Fig. 4). The
EP in both systems, however, is caused by the nitrogen oxides that are
emitted through the process delivery.
The overall results show that the delivery of rebars in the
prefab-JIT system causes less damage to the environment, compared with
their delivery in the on-site fabrication system. This happens mainly
due to the lower use of fuel- and electricity-powered equipment and the
smaller rates of rebar loss in the prefab-JIT delivery system. In other
words, making a delivery system more efficient and less wasteful, which
occurs in the case of prefab-JIT system, also results in less
environmental damage.
[FIGURE 4 OMITTED]
5.5. Limitations and recommendations
Data quality is considered as a primary concern with respect to an
LCA study. In fact, the lack of reliable representative data, as well as
the uncertainties surrounding the subject of LCA studies, affects the
validity and reliability of the results. In the case of this study, many
players in the rebar supply chain were needed to be reached and
interviewed to acquire the needed data. While this was done through the
course of this study, investigating more stakeholders in the industry
and comparing the data they provide offer a better opportunity for
achieving more reliable results. In addition, this research in some
cased used the data provided by the publicly available inventory
databases to fill the data gaps. Some of these data did not represent
the unit processes in this study with respect to the time horizon,
geographic location, precision, etc.; as a result of which the overall
data and results' quality will be impacted. It is recommended that
future research considers collection of representative data from several
primary sources in order to improve the data quality issue.
Also due to the lack of resources, this study conducted a
cradle-to-gate LCA study instead of a more comprehensive one which
includes a full life cycle of the subject of the study. It is
recommended that all life cycle phases in both delivery systems are
included in a future research.
Another limitation in this research has to do with the research
validation. Unfortunately, the authors could not find any other research
on the specific subject of this paper whose results could be used for
comparison purposes in order to validate its results. Future research on
this subject can use the results of this paper to highlight the
differences and their sources.
Finally, this research targets a few environmental impact
categories for assessing the two systems. It ignores a wide range of
other environmental and health impact categories. It also fails to study
the social and cost impacts of the two systems. It is recommended that
future research expands this study not only within the environmental
impact categories but also with respect to other impacts important to
the triple-bottom approach. Doing this will provide a better framework
to compare the two systems.
Conclusions
The efficient delivery of reinforced steel rebars is a critical
factor in achieving cost and time targets in construction projects. The
studies that address the efficiency of delivery systems mostly focus on
the process improvements, lead time reductions, and the waste reduction.
The environmental impacts are rarely addressed in these studies.
The current study on the environmental impacts of the on-site
fabrication and prefab-JIT rebar delivery systems revealed that more
efficient, less wasteful delivery systems bring environmental
advantages, too. It is especially important to inform contractors that
the implementation of wasteful processes not only results in time and
cost overruns but also damages the surrounding environment. Also, more
research on materials should be encouraged to explore more improvements
in their management and delivery processes in order to reduce the wastes
through the systems.
http://dx.doi.org/ 10.3846/13923730.2013.795186
Acknowledgments
This work was supported by the National Research Foundation of
Korea's Grant funded by the Korean Government
(NRF-2010-013-D00080). The authors would like to thank Professor Joyce
Cooper for her valuable comments on the project.
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Yong-Woo KIM (a), Rahman AZARI-N (a), June-Seong YI (b), Jinwoo BAE
(a)
(a) College of Built Environments, University of Washington,
Seattle, WA, USA
(b) Department of Architectural Engineering, Ewha Womans
University, Seoul, South Korea
Received 21 Sep. 2011; accepted 14 Dec. 2011
Yong-Woo KIM. Associate Professor and P.D.Koon Endowed Professor of
Construction Management at the University of Washington, Seattle, WA,
USA. He is a member of Lean Construction Institute (LCI) and ASCE. His
research interests include lean construction, supply chain management,
and activity-based costing.
Rahman AZARI-N. PhD Candidate in Built Environment at the
University of Washington, Seattle, Washington, USA. With a background in
architectural engineering, his main research interests focus on green
building design and delivery, life cycle assessment (LCA) of buildings,
building information modeling (BIM), and energy-efficient building
design.
June-Seong YI. Associate Professor in the Department of
Architectural Engineering at Ewha Womans University, Seoul, Korea. He is
a member of Association for the Advancement of Cost Engineering (AACE).
His research interests include strategic cost management, supply chain
management, and Life-Cycle Assessment (LCA) of buildings.
Jinwoo BAE. Former graduate student of construction engineering and
management program at the University of Washington, Seattle, WA, USA.
His research interests include lean construction and building
information modeling.
Corresponding author: June-Seong Yi
E-mail: jsyi@ewha.ac.kr
Table 1. Differences between on-site fabrication and
prefab-JIT delivery systems in the case study
Item On-site Prefab-JIT
fabrication system system
Equipment operating hours
Crane 11 7.4
Rebar bender/cutter 5.5 5
Forklift 26 18
Delivery distance (mile) 27 32
Rebar loss rate (%) 10 3
Batch size per truck (ton) 25 21
Rejection rate in 5 2
inspection by GC (%)
Item Comment
Equipment operating hours
Crane Diesel powered, capacity: 450 hp
Rebar bender/cutter Electricity powered, capacity: 1200 W
Forklift Diesel powered, capacity: 76 hp
Delivery distance (mile)
Rebar loss rate (%) Total installation amount: 80 tons
Batch size per truck (ton)
Rejection rate in Delivered fabricated rebar
inspection by GC (%)
Table 2. Unit processes and inventory data sources
Process category Unit processes Data sources
Rebar production Raw rebar production --GREET (for
recycled steel)
--Data at rebar
production plant
Prefabrication --Data at rebar
(cutting and bending) prefabrication
of the raw rebar plant
--diesel-powered
traveling overhead
cranes and tower cranes
Subassembly of the --NONROAD model
fabricated rebar in an
assembly yard using
propane-powered forklifts
Energy production Electricity production --GREET
Diesel production
Propane production
Transport Delivery of the raw --GREET
rebar to the prefabrication
plant using Heavy-Heavy --NONROAD model
Truck--class 8a or 8b
(20 ton cargo), 5.0 mpg,
100% load, 5%
urban emissions
--Data at rebar
production plant
--Data at rebar
prefabrication
plant
Backhaul with scrap
using Heavy-Heavy
truck--class
8a or 8b (20 ton cargo),
5.0 mpg, 100% load, 5%
urban emissions
Moving fabricated
rebar to an
assembly yard using
propane-powered forklifts
Delivery of the
assembled rebar to
a construction site
using Heavy-Heavy
truck--class 8a or
8b (20 ton
cargo), 5.0 mpg, 100%
load, 5% urban emissions
Installation Unloading the --NONROAD model
delivered rebar
assembly using --General
propane-powered Contractor
forklifts (GC) data
Installation of the
rebar assembly using
diesel-powered
tower crane
Table 3. Inventory results for the traditional
and prefab-JIT delivery systems
Emissions Traditional Prefab-JIT Difference (kg)
system (kg) system (kg)
Carbon dioxide 5.82E + 08 5.34E + 08 4.82E + 07
Carbon monoxide 2.12E + 06 1.96E + 06 1.65E + 05
Methane 4.38E + 05 3.85E + 05 5.38E + 04
Nitrogen oxides 4.35E + 06 4.06E + 06 2.89E + 05
Nitrous oxide 2.76E + 03 2.42E + 03 3.39E + 02
NMVOC 2.71E + 05 2.53E + 05 1.84E + 04
Sulfur oxides 8.32E + 05 7.64E + 05 6.86E + 04
Table 4. Classification of environmental outputs
Emissions Environmental impact category
Carbon dioxide Global warming
Carbon monoxide Smog formation
Methane Global warming, smog formation
Nitrogen oxides Acidification, Eutrophication,
Smog formation
Nitrous oxide Global warming
NMVOC Smog formation
Sulfur oxides Acidification
Table 5. Contribution analysis of the delivery methods using TRACI
Delivery system Emission GWP (kg C[O.sub.2]-e)
Traditional Carbon dioxide 5.82E+ 08
system Carbon monoxide 0
Methane 9.21E + 06
Nitrogen oxides 0
Nitrous oxide 8.57E+ 05
VOCs 0
Sulfur oxides 0
Total contribution 5.92E+ 08
Prefab-JIT Carbon dioxide 5.34E+ 08
system Carbon monoxide 0
Methane 8.08E+ 06
Nitrogen oxides 0
Nitrous oxide 7.52E+ 05
VOCs 0
Sulfur oxides 0
Total contribution 5.42E+ 08
Difference 4.95E+ 07 (8.36%)
Delivery system Emission AP (H+ moles-e)
Traditional Carbon dioxide 0
system Carbon monoxide 0
Methane 0
Nitrogen oxides 1.74E + 08
Nitrous oxide 0
VOCs 0
Sulfur oxides 4.23E+ 07
Total contribution 2.16E + 08
Prefab-JIT Carbon dioxide 0
system Carbon monoxide 0
Methane 0
Nitrogen oxides 1.62E + 08
Nitrous oxide 0
VOCs 0
Sulfur oxides 3.88E+ 07
Total contribution 2.01E+ 08
Difference 1.51E + 07 (6.96%)
Delivery system Emission EP (kg N-e)
Traditional Carbon dioxide 0
system Carbon monoxide 0
Methane 0
Nitrogen oxides 1.93E+ 05
Nitrous oxide 0
VOCs 0
Sulfur oxides 0
Total contribution 1.93E+ 05
Prefab-JIT Carbon dioxide 0
system Carbon monoxide 0
Methane 0
Nitrogen oxides 1.80E+ 05
Nitrous oxide 0
VOCs 0
Sulfur oxides 0
Total contribution 1.80E+ 05
Difference 1.28E+ 04 (6.65%)
Delivery system Emission SP (kg NOx-e)
Traditional Carbon dioxide 0
system Carbon monoxide 3.53E+ 04
Methane 1.61E + 03
Nitrogen oxides 5.39E+ 06
Nitrous oxide 0
VOCs 2.63E+ 05
Sulfur oxides 0
Total contribution 6.10E + 06
Prefab-JIT Carbon dioxide 0
system Carbon monoxide 3.25E+ 04
Methane 1.41E+ 03
Nitrogen oxides 5.03E+ 06
Nitrous oxide 0
VOCs 2.45E+ 05
Sulfur oxides 0
Total contribution 5.31E+ 06
Difference 3.79E+ 05 (6.67%)
