Wonjae Choi

Reusable tumblers are widely perceived as an environmentally friendly alternative to disposable cups; however, their actual environmental benefits may be overestimated if the initial impacts from manufacturing and the burdens associated with repeated washing are not adequately considered. This study evaluated the life-cycle greenhouse gas (GHG) emissions of 12 oz (355 mL) PE-coated paper cups, PET cups, and stainless-steel tumblers, and analyzed the environmental break-even points of reusable tumblers under different washing methods. All products were assessed within a cradle-to-grave system boundary covering production, transportation, use, and end-of-life. Life-cycle inventories were developed using ecoinvent and Korea-specific data on supply chains, electricity, water, and waste treatment. For the tumbler use phase, manual washing with cold or hot water, foaming detergent washing, household dishwasher use, and a dedicated tumbler cleaner were compared. The results showed that GHG emissions per use were 42.8 g-CO2-eq. for the paper cup and 77.8 g-CO2-eq. for the PET cup, with material production being the largest contributor for both cup types. The initial GHG emissions of the tumbler were 923.4 g-CO2-eq. per unit, and the environmental break-even point varied substantially depending on the washing method. Manual cold-water washing resulted in the lowest washing burden, whereas the dedicated tumbler cleaner did not reach a break-even point under the analyzed conditions because of its relatively high electricity consumption. These results demonstrate that the environmental benefit of reusable tumblers depends not simply on reuse itself, but on a sufficient number of cumulative uses and low-energy washing conditions.

Conventional life cycle assessments of aluminium often rely on global average emission factors, overlooking the fact that import-dependent manufacturing countries are exposed to highly heterogeneous upstream supply chains. This leads to substantial misestimation of material-related greenhouse gas (GHG) emissions. This study develops an import mix-based life cycle GHG emissions database for aluminium ingots, accounting for supplier-specific production intensities, trade composition, and transportation, following ISO 14040/14044. South Korea is used as a case study, with implications for other import-dependent economies. The GHG emissions of conventional aluminium production are estimated at 17.5 ton-CO₂-eq./ton-Al. Four alternative production pathways—electrification, inert anodes, carbon capture and storage (CCS), and recycling—achieve emission reductions of 7.2%, 4.1%, 7.3%, and 92%, respectively. Sensitivity analysis reveals that year-to-year variations in import mix alone can reduce emissions by up to 17.9%, exceeding the mitigation potential of all alternative technologies except recycling. These aluminium emissions are integrated into EV lightweighting life cycle analysis, coupling vehicle mass, battery capacity, and fuel economy changes, based on vehicle simulations using GT SUITE. Replacing 50% of steel with aluminium increases life cycle GHG emissions by 22%, because the added burden from vehicle materials manufacturing exceeds the reduction from battery manufacturing and vehicle operation. Lightweighting becomes environmentally beneficial when primary aluminium emissions decrease below 3.8 ton-CO₂-eq./ton-Al or the secondary aluminium share exceeds 66%. As the steel substitution rate increases, these requirements become more stringent. The proposed framework highlights the critical role of supply chains and energy systems in determining the climate benefits of aluminium lightweighting and is transferable to other import-dependent regions.

Conventional life cycle assessments of aluminium often rely on global average emission factors, overlooking the fact that import-dependent manufacturing countries are exposed to highly heterogeneous upstream supply chains. This leads to substantial misestimation of material-related greenhouse gas (GHG) emissions. This study develops an import mix-based life cycle GHG emissions database for aluminium ingots, accounting for supplier-specific production intensities, trade composition, and transportation, following ISO 14040/14044. South Korea is used as a case study, with implications for other import-dependent economies. The GHG emissions of conventional aluminium production are estimated at 17.5 ton-CO₂-eq./ton-Al. Four alternative production pathways—electrification, inert anodes, carbon capture and storage (CCS), and recycling—achieve emission reductions of 7.2%, 4.1%, 7.3%, and 92%, respectively. Sensitivity analysis reveals that year-to-year variations in import mix alone can reduce emissions by up to 17.9%, exceeding the mitigation potential of all alternative technologies except recycling. These aluminium emissions are integrated into EV lightweighting life cycle analysis, coupling vehicle mass, battery capacity, and fuel economy changes, based on vehicle simulations using GT SUITE. Replacing 50% of steel with aluminium increases life cycle GHG emissions by 22%, because the added burden from vehicle materials manufacturing exceeds the reduction from battery manufacturing and vehicle operation. Lightweighting becomes environmentally beneficial when primary aluminium emissions decrease below 3.8 ton-CO₂-eq./ton-Al or the secondary aluminium share exceeds 66%. As the steel substitution rate increases, these requirements become more stringent. The proposed framework highlights the critical role of supply chains and energy systems in determining the climate benefits of aluminium lightweighting and is transferable to other import-dependent regions.