Electric light-duty vehicles have decarbonization potential but may not reduce other environmental problems

Transportation is a major contributor to greenhouse gas emissions, with light-duty vehicles being a primary source. Electric vehicles (EVs), particularly battery electric vehicles (BEVs), are promoted as a solution. The rapid growth of the EV market is driven by their potential to decarbonize transportation, especially when charged with low-carbon electricity. However, the well-to-wheel emissions of EVs vary significantly depending on the local electricity grid's fuel mix. In countries with grids heavily reliant on fossil fuels, EVs may have higher emissions than internal combustion engine vehicles (ICEVs). Academic studies highlight the critical role of electricity grid mixes in determining the environmental impacts of EVs, with the grid mix accounting for a substantial portion of EVs' lifetime carbon emissions. This study aims to conduct a comprehensive life cycle assessment (LCA) to compare the lifecycle environmental impacts of four dominant light-duty vehicle categories: ICEVs, HEVs, PHEVs, and BEVs, considering various environmental indicators beyond just global warming potential (GWP), such as respiratory effects. The study focuses on a global perspective and includes case studies of Norway, the US, and China, representing diverse electricity grid mixes and transportation profiles. The study also accounts for the dynamic nature of the evolving grid towards cleaner energy sources.

Existing literature extensively examines the global warming potential (GWP) of EVs, showing promising reductions in GWP compared to ICEVs in regions with cleaner electricity grids. Studies have demonstrated significant reductions in lifecycle GWP for BEVs compared to ICEVs in various regions, including the US, European Union, and China. However, the literature also recognizes the importance of mitigating respiratory effects (RE) caused by transportation emissions, particularly from fine particulate matter (PM2.5). Studies have shown both positive and negative impacts of EVs on RE, with some suggesting potential increases in PM2.5 emissions from electricity generation. The uneven distribution of EV emissions and its relation to environmental justice is also addressed, highlighting that while urban populations might benefit most from zero tailpipe emissions, rural or low-income communities could bear more significant environmental burdens from electricity generation.

This study uses a cradle-to-grave life cycle assessment (LCA) following ISO 14040 and 14044 guidelines to compare ICEVs, HEVs, PHEVs, and BEVs. The analysis considers vehicle construction, operation, maintenance, and end-of-life phases. A driving distance of 320,000 km is assumed for each vehicle. The openLCA software (version 2.1) is used, incorporating data from the Ecoinvent 3.7 database and the GREET 2022 model. The study considers both current and future grid mixes. For future projections, the International Energy Agency's (IEA) World Energy Outlook 2023 Stated Policies Scenario (STEPS) and Announced Pledges Scenario (APS) are utilized to model the 2030 grid mix for the US and China. The 2030 STEPS scenario acts as a baseline representing the most likely outcome under conservative assumptions, with APS representing more aggressive changes in the grid mix. The vehicle lifecycle is divided into vehicle cycle (manufacturing, maintenance, disposal) and fuel cycle (fuel extraction, combustion, electricity production). Two key impact metrics are analyzed: GWP and RE. The analysis also investigates the influence of PHEV electric driving share and BEV electricity consumption on the results. Uncertainty analysis is performed by adjusting key parameters based on data from currently available medium-sized vehicles. The study examines both global and country-level results (Norway, US, China) to account for regional variations in electricity grid mixes.

The vehicle cycle analysis shows that BEVs have the highest GWP and RE compared to other vehicle types, primarily due to battery production emissions. Across all regions, ICEVs occupy a small portion of the 'lowest GWP' landscape in the analysis, showing that BEVs' dominance depends on various factors. In the current scenario, BEVs have the lowest GWP only under specific conditions: high lifetime driving distances and low to moderate PHEV electric driving shares, and cleaner electricity grid mixes (Norway). In China, with a high-emission grid, HEVs consistently outperform BEVs and PHEVs in terms of GWP due to high electricity generation emissions. Under the STEPS and APS scenarios (representing future grid clean-up), BEVs' advantage expands, outperforming HEVs and PHEVs in both the US and China. Regarding respiratory effects, in the current scenario, ICEVs have the lowest RE initially, but HEVs take over at higher driving distances for most regions except Norway. In both STEPS and APS scenarios, HEVs consistently outperform other vehicle types in terms of RE. The breakdown of RE into tailpipe and non-tailpipe emissions reveals that non-tailpipe emissions (electricity generation and well-to-tank processes) are the primary contributors, even for ICEVs, suggesting that EVs might shift pollution from tailpipes to electricity generation sites. The study also finds that increasing PHEV electric driving share can lead to higher total respiratory effects. This is because non-tailpipe emissions from electricity production are often higher than those from gasoline combustion. In general, BEVs have higher respiratory effects than HEVs even under the cleaner APS scenarios.

The findings demonstrate that EVs' environmental benefits are strongly linked to the cleanliness of the electricity grid. While EVs offer substantial decarbonization potential with cleaner grids, they may not fully mitigate other environmental impacts, especially RE. This highlights that decarbonization alone is insufficient for achieving holistic environmental sustainability. The study's results suggest a geographical shift in pollution sources rather than a complete reduction, raising environmental justice concerns. The increased RE from electricity generation could disproportionately affect lower-income or rural communities near power plants. The choice between BEVs and PHEVs involves a trade-off between range and emissions; BEVs have longer ranges but higher lifecycle emissions due to larger battery packs, while PHEVs offer lower emissions when used primarily on electric power, but a shorter range. Consumer decisions should account for factors like lifetime driving distance, daily commuting distance, and PHEV electric driving share, which interact with regional differences in grid mix and charging infrastructure.

EVs are not inherently 'clean' solutions; their environmental performance depends on the electricity grid's composition. While EVs offer decarbonization potential, they may not mitigate all environmental impacts, particularly RE. The transition to electrified transportation might shift and potentially exacerbate pollution in vulnerable communities. Future research should focus on regional variations in EV charging behaviors, alternative battery technologies, and more comprehensive datasets to improve the accuracy of LCA analysis. Policymakers should consider tailored strategies and incentives based on regional contexts, focusing on improving grid cleanliness and addressing environmental justice concerns.

The study acknowledges limitations, including the exclusion of the battery end-of-life phase due to data scarcity, and the use of average values for certain parameters that may not fully capture the spectrum of real-world conditions. The analysis also does not provide state-level or local comparisons of electricity grid mixes. Future research should address these limitations using improved and more comprehensive datasets and refined analysis methods.