Page 73 - Materials Chemistry, Second Edition

The Application of Life Cycle Assessment on Agricultural 59

A LCIA attempts to establish a linkage between the product or process and its
potential environmental impacts. Critical questions for example:
• What are the impacts of that much quantity of CO 2 or that much quantity of
methane emissions being released into the atmosphere by a typical beef farm
annually?
• Which is more damaging to air pollution?
Typical midpoint environmental impact categories considered mostly in LCA
are as follows: (1) the greenhouse effect (global warming potential), (2) eutro-
phication potential, (3) acidification potential, (4) formation of photochemical
oxidants, (5) particles, and (6) energy balance (Borjesson et al. 2011). More
particularly, the global warming potential refers to the increase in the average
temperature of the Earth’s surface, due to an increase in the global warming
potential, caused by anthropogenic emissions of global warming gases such as
carbon dioxide, methane, nitrous oxide, fluorocarbons, e.g., CFCs and HCFCs, and
others. Acidification refers to the accumulation of acidifying substances, e.g.,
sulfuric acid, hydrochloric acid in the water particles in suspension in the atmo-
sphere which are deposited onto the ground by rains; acidifying pollutants have a
wide variety of impacts on soil, groundwater, surface waters, biological organisms,
ecosystems, and materials, e.g., buildings. Eutrophication which is a process
whereby water bodies, such as lakes or rivers, receive excess chemical nutrients,
typically compounds containing nitrogen or phosphorus that stimulate excessive
plant growth, e.g., algae. Nutrients can come from many sources, such as fertilizers
applied to agricultural fields, deposition of nitrogen from the atmosphere, erosion
of soil containing nutrients, and sewage treatment plant discharges (Wenisch and
Monier 2007). An LCIA provides a systematic procedure for classifying and
characterizing these types of environmental effects. GHGs emissions, for example,
from different sources are indexed according to their global warming potential.
According to the intergovernmental panel on climate change (IPCC 2001), over a
100-year time span, carbon dioxide (CO 2 ) assumes the value of 1 whereas the two
other GHGs of importance in agriculture LCA are methane (CH 4 ) and nitrous
oxide (N 2 O) which, according to a re-evaluation of the IPCC in 2001, take a value
of 23 and 296 respectively. Hence, the volume of GHG emissions in terms of CO 2 e
can be calculated using Eq. (8) (IPCC 2001;EC 2009):

GHG kg of CO eð Þ ¼ CO 2 kgð Þ þ 23 CH 4 kgð Þ þ 296 N 2 OðkgÞ ð8Þ
2
Midpoint impact assessment approaches reflect the relative potency of the
stressors at a common midpoint within the cause–effect chain. Analysis at a
midpoint minimizes the amount of forecasting and effect modeling incorporated
into the LCIA, thereby reducing the complexity of the modeling and often sim-
plifying communication. Midpoint modeling can minimize assumptions and value
choices, reflect a higher level of societal consensus, and be more comprehensive
than model coverage for endpoint estimation. (Bare et al. 2003). Endpoints
depicted in Fig. 11 belong to a larger, more generic impact category, e.g., ‘‘skin