A characterization model with spatial and temporal resolution for life cycle impact assessment of photochemical precursors in the United States |
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Authors: | Viral P Shah Robert J Ries |
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Institution: | (1) Department of Civil and Environmental Engineering, University of Pittsburgh, 949 Benedum Hall, Pittsburgh, PA 15213, USA;(2) M.E. Rinker, Sr. School of Building Construction, University of Florida, 304 Rinker, P.O. Box 115703, Gainesville, FL 32611, USA |
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Abstract: | Background, aim, and scope Traditional life cycle impact assessment methodologies have used aggregated characterization factors, neglecting spatial and
temporal variations in regional impacts like photochemical oxidant formation. This increases the uncertainty of the LCA results
and diminishes the ease of decision-making. This study compares four common impact assessment methods, CML2001, Eco-indicator
99, TRACI, and EDIP2003, on their underlying models, spatial and temporal resolution, and the level at which photochemical
oxidant impacts are calculated. A new characterization model is proposed that incorporates spatial and temporal differentiation.
Materials and methods A photochemical air quality modeling system (CAMx-MM5-SMOKE) is used to simulate the process of formation, transformation,
transport, and removal of photochemical pollutants. Monthly characterization factors for individual US states are calculated
at three levels along the cause–effect chain, namely, fate level, human and ecosystem exposure level, and human effect level.
Results and discussion The results indicate that a spatial variability of one order of magnitude and a temporal variability of two orders of magnitude
exist in both the fate level and human exposure and effect level characterization factors for NOx. The summer time characterization factors for NOx are higher than the winter time factors. However, for anthropogenic VOC, the summer time factors are lower than the winter
time in almost half of the states. This is due to the higher emission rates of biogenic VOCs in the summer. The ecosystem
exposure factors for NOx and VOC do not follow a regular pattern and show a spatial variation of about three orders of magnitude. They do not show
strong correlation with the human exposure factors. Sensitivity analysis has shown that the effect of meteorology and emission
inputs is limited to a factor of three, which is several times smaller than the variation seen in the factors.
Conclusions Uncertainties are introduced in the characterization of photochemical precursors due to a failure to consider the spatial
and temporal variations. Seasonal variations in photochemical activity influence the characterization factors more than the
location of emissions. The human and ecosystem exposures occur through different mechanisms, and impacts calculated at the
fate level based only on ozone concentration are not a good indicator for ecosystem impacts.
Recommendations and perspectives Spatial and temporal differentiation account for fate and transport of the pollutant, and the exposure of and effect on the
sensitive human population or ecosystem. Adequate resolution for seasonal and regional processes, like photochemical oxidant
formation, is important to reduce the uncertainty in impact assessment and improve decision-making power. An emphasis on incorporating
some form of spatial and temporal information within standard LCI databases and using adequately resolved characterization
factors will greatly increase the fidelity of a standard LCA.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Characterization model LCA sophistication Spatial resolution Temporal resolution Tropospheric ozone |
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