Future in- and out-of-state air pollutant emissions under decarbonization pathways for Massachusetts

Many U.S. states have adopted the goal of achieving carbon neutrality in the coming decades. Pathways for achieving these targets would likely yield a reduction of air pollutant emissions as well. We assess several state-level decarbonization pathways for Massachusetts, including electrification of buildings and transportation and decarbonization of the electric grid, estimating their impacts on in- and out-of-state emissions of carbon dioxide (CO 2 ) and several air pollutants. The analysis applies the GCAM-USA integrated assessment model with state-level resolution. We consider interactions between existing and proposed state and regional policies. The most aggressive state decarbonization pathway that was examined would achieve only a 65% reduction in CO 2 emissions by 2050 relative to 2015, indicating the need for further decarbonization options within the industry and non-road transportation sectors to achieve net-zero emission goal stated by the current administration. The air pollution co-benefits under these decarbonization pathways are substantial, especially for primary fine particulate matter. While policies focusing only on Massachusetts are shown to deliver in-state reductions of CO 2 and air pollutant emissions, these reductions were partially countered by emissions increases in other states, indicating the need for coordinated regional planning to prevent emissions leakage.