Air Quality, Health and Equity Impact Assessment of the Transportation Climate Initiative

Abstract:

In the United States, the transportation sector generates the largest share (28.2%) of greenhouse gas (GHG) emissions. Twelve East Coast states and the District of Columbia have joined the Transportation Climate Initiative (TCI) to create a regional cap-and-invest program to reduce transportation-sector GHG emissions. We implemented a multi-model approach to estimate the air quality, physical activity, health, and equity implications of a number of different cap-and-invest scenarios. To assess the air quality impacts, we modeled how changes in SO₂, NO_X, NH₃, VOC, and PM_2.5 emissions from each scenario would impact air quality at a 21x12 km grid scale across the region using the Community Multiscale Air Quality (CMAQ) model with the Decoupled Direct Method (DDM). We then used literature-based concentration-response functions for both child and adult health outcomes, and estimated grid level changes in health outcomes using USEPA BenMAP tool in R. We used the Atkinson Index to quantify how these changes in concentrations and corresponding health outcomes would ameliorate or exacerbate inequalities across different racial, ethnic, and income groups. Finally, as the TCI cap-and-invest program is expected to shift transportation modes to more active forms of mobility, namely cycling and walking, we also conducted an analysis of the mortality benefits of additional physical activity in each county using the World Health Organization HEAT tool. Our model results indicate that substantial health benefits for both adults and children can be realized by 2032 across the region under cap and invest scenarios that reduce GHG emissions by 20%, 22%, and 25%, primarily driven by changes in PM_2.5 and O₃ concentrations. Inequality analyses indicate exposure and health outcome inequalities associated with baseline concentrations, with differential effects on inequality across different policy options. Mortality benefits associated with physical activity generally exceeded those associated with air pollution reductions in urban areas. Our analyses reinforce the value of multi-model health impact assessments for estimating the magnitude and distribution of health co-benefits of policies options for reducing GHG emissions.