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Background, Aim and Scope:
The goal of this work is to provide methodological information for modeling commodity transport in LCA. The scope includes a review of transport modeling results in LCA studies, transport modeling parameters, and backhaul (or return trip) and distance estimation assumptions. A case study estimates the contribution of transport to the domestic production of US steel to demonstrate the importance of well conceived and documented assumptions.
Materials and Methods:
Transport energy consumption and emissions are varied as a function of assumptions for transportation mode, distances traveled, and backhaul considerations. The scope includes raw materials acquisition for electricity, fuels, and other inputs to steel production, through iron and steel production (by blast oxygen furnace and electric arc furnace) and sheet rolling. The analysis includes 99.9 mass% of unit process inputs, with the exception of the production of explosives . The results track life cycle total, fossil, and petroleum energy consumption and eight air emissions: CH4, CO, CO2, N2O, NOx, PM, SOx, and NMVOC. All ISO 14040 series information for this study (for goal and scope definition, inventory analysis, impact assessment, data quality analysis, and interpretation) are presented in the primary reference.
Results:
For the steel case study, commodity transportation’s percent contribution to the life cycle emissions of NOx, NMVOCs, and N2O are of particular importance, topping out at 37.6% of the life cycle NOx emissions for Blast Oxygen Furnace steel. Normalization of the results finds steel life cycle emissions of SOx, NOx, PM, and CO2 to range from 0.1-1.1% of the total US transportation system emissions with the variation in SOx emissions due to backhaul and distance assumptions representing 0.6% of the US transportation value.
Discussion:
Transportation can be an important contributor to petroleum consumption and emissions and that these values vary based on distance and backhaul assumptions. Despite these findings and those of select LCA practitioners, little published methodological information detailing what or how transportation should be included is found in LCA literature. General methodological guidance is however presented by the SETAC (Society of Environmental Toxicology and Chemistry) LCA Working Group on Data Availability and Data Quality subgroup with few details on implementation.
Conclusions:
Transportation can be an important contributor to a system’s life cycle. LCA studies should ensure assumptions for transportation mode mix, backhaul, distance estimation, and co-location are fully described in study documentation. Further, when including the contribution of transportation as part of LCA results, the contribution should include transportation fuel production energy use and emissions.
Recommendations and
Perspectives:
Additional case study commodities and detailed guidelines for assumptions made in transport modeling should be included in future work. Important in these efforts will be the further analysis of data quality and uncertainty and sensitivity analysis; assessment of a broader range of environmental flows; inclusion of transportation at facilities and ports/stations, accidents, and waste transport; and modeling transportation from and to overseas destinations.
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