Comparing first to diesel buses, across a majority of zones, PM2.5 is reduced by electrification of school buses (the absence of an orange bar indicates that an electric school bus outperforms a diesel bus in that zone). This finding highlights the substantial air quality benefits that can be realized by electrifying high-emitting diesel bus fleets, even in regions with a relatively modest contribution of renewables or clean energy sources in their electricity generation portfolios. The four regions in Alaska and Hawaii are the only zones where electrification leads to an increase of PM2.5 over a diesel bus – everywhere else, converting from diesel to electric is a clear win-win.

Comparing next to gasoline buses, every zone in the country requires additional greening, and in all but two New York zones, to the tune of 50% or more. Despite this finding, we advocate for rapid electrification of school buses and simultaneous improvement in the fraction of renewable electricity in the coming years.

In the above analysis, in order to simplify the calculation, we assumed that usage of each fossil fuel in the mix would be reduced by the same percentage. However, depending on fuel source and other technical considerations, some electrical generation systems pollute much more than others. Greening the most polluting systems first will reduce PM2.5 emissions more rapidly than indicated by the results above.

Policy Implications and Regional Priorities

The findings reveal significant variations in clean energy requirements across eGRID zones and vehicle categories. While transportation electrification offers promising carbon emission reductions, its impacts on PM2.5 emissions and air quality are region-specific.

• Electrification should proceed post haste, and will yield additional GHG and PM2.5 benefits as the electricity supply is made cleaner in coming years.
• Policymakers and stakeholders should prioritize greening the grid in regions with high clean energy conversion needs, to ensure a comprehensive approach to air quality improvement, particularly in the case of light-duty vehicles and gasoline-powered buses. Furthermore, prioritizing substitution of the most polluting generation sources in these regions will yield the greatest air quality improvement for a given level of investment. Roughly speaking, coal and other ash-producing solid fuels should be abated before oil, and oil before natural gas. Getting rid of natural gas, however, has a huge impact on GHG reduction due to avoidance of methane leakage.
• Conversely, regions with positive PM2.5 attributes, especially for diesel school buses, present opportunities for accelerated electrification efforts, as electric buses already offer substantial air quality benefits in addition to GHG reduction.

As the grid transitions towards cleaner energy sources, the air quality benefits of transportation electrification will become more pronounced across all regions and vehicle categories, and the gains will be “automatic” as the grid is cleaned up. So, it is not advisable at this time to invest in a gasoline or diesel vehicle that may be driven for 10 or more years.

Ultimately, a holistic strategy that addresses both transportation electrification and grid decarbonization is essential to achieve the “win-win-win” scenario of reduced costs, improved air quality, and mitigated climate impacts. Such a strategy would include aggressive electrification of transportation, build-out of charging infrastructure, acceleration of permitting and deployment of renewable energy sources, investment in transmission, and stringent emissions standards for power plants.

Environmental Justice Considerations

It is also crucial to consider the environmental justice implications of this transition. Electromobility shifts PM2.5 from the tailpipe in the locale where the vehicle is driven to a possibly remote power plant. Disadvantaged communities bear a disproportionate burden of air pollution from fossil power plants and industrial facilities. As transportation electrifies, there is a risk of further concentrating PM2.5 emissions in these vulnerable areas unless proactive measures are taken to clean up the energy supply chain.

Policymakers must engage with impacted communities in each zone, implement robust monitoring and enforcement mechanisms, and explore innovative solutions such as distributed renewable energy generation and energy storage in parallel with electromobility to mitigate potential environmental injustices.

Conclusion

The road to a sustainable transportation future is complex, requiring a nuanced, zone-specific approach that balances the global benefits of reducing greenhouse gas emissions with localized air quality impacts and environmental justice considerations. The data presented in this analysis underscores the need for tailored strategies that consider the unique clean energy requirements and PM2.5 implications of vehicle electrification in different regions. By prioritizing the most impactful vehicle classes and zones, accelerating the transition to clean energy sources, and addressing environmental justice concerns, we can maximize the benefits of transportation electrification while safeguarding public health and promoting equitable access to clean air across all communities. Given the urgency of the climate crisis, electrification of transportation should proceed full steam ahead, even if PM2.5 gains will only accrue in subsequent years.

Appendix A (more information)

Appendix B (more information here and here)