Page 69 - Materials Chemistry, Second Edition

LIFE CYCLE INVENTORY MODELING IN PRACTICE 51

transportation distances. Some materials have international raw material sup-
ply chains that are dependent on the geographic distribution of ores and other
natural resources. Other processes may be specifically located to take advan-
tage of material or energy supplies. For example, electricity-intensive alumina
smelting operations are sited to take advantage of hydropower. Modeling the
aluminum supply chain using average U.S. grid electricity for all the processes
would result in a large overstatement of carbon dioxide emissions associated
with smelting.
Other operations tend to be widely distributed, for example, converting
operations such as plastic molding facilities. The locations of raw materials
and subsequent processing operations should be taken into account when
modeling transportation distances between life cycle stages or choosing elec-
tricity grids for process energy at different life cycle stages.
Regional issues are especially influential when evaluating agricultural sys-
tems. Regional differences in climate, soil composition, rainfall, etc. can result
in significant regional variations in crop yields, irrigation requirements, and
applications and runoff of agricultural chemicals.
Geographic boundaries also influence end-of-life scenarios. Recycling rates
for products may vary widely from country to country or from region to region
within a country, influenced by legislation, consumer behavior, and access to
recycling programs. For example, beverage container recycling rates in U.S.
states with deposit laws are higher than recycling rates for states without
deposit laws. Landfill space is limited in some regions, while other regions
may not have access to waste-to-energy combustion facilities. For material that
is landfilled at end of life, local conditions such as temperature, moisture, etc.
will affect the degree and rate at which biodegradable materials decompose
(or fail to decompose) in a local landfill.
Time Boundaries. Similar to geographic boundaries, time boundaries can
influence the accuracy and relevance of study results. Systems should be modeled
using the technology or mix of technologies that is relevant for current production
in the region where processes take place. End-of-life management practices also
change over time in response to increasing environmental awareness of consum-
ers, legislative measures, and access to different recycling and disposal options.
For long-lived products that have significant use-phase energy impacts, such
as building insulation, greenhouse gas savings over time may be influenced by
shifts in the energy supply (e.g., from fossil fuel-based electricity generation to
more wind and solar electricity, or more use of biomass fuels), even if the prod-
uct's properties do not change over time. In other words, an insulation product
may provide consistent insulating performance over a 50-year lifetime, but
annual greenhouse gas savings over time could become smaller as the energy
supply becomes less carbon-intensive.
Impact Categories. When scoping a project, it is important to define the
impact categories that will be included in the results, as this influences the data
collection requirements. A study scoped as a life cycle carbon footprint analy-
sis will have very different data requirements than a study that includes a full
set of life cycle impact indicators.